Electromyography is a method of studying the neuromuscular system by recording the electrical potentials of the muscles. Electromyography is an informative method for diagnosing diseases of the spinal cord, nerves, muscles and neuromuscular transmission disorders. Using this method, it is possible to study the structure and function of the neuromotor apparatus, which consists of functional elements - motor units (MU), which include a motor neuron and the group of muscle fibers innervated by it. During motor reactions, several motor neurons are simultaneously excited, forming a functional association. On the electromyogram (EMG), potential fluctuations in the neuromuscular endings (motor plates) are recorded, which occur under the influence of impulses from the motor neurons of the medulla oblongata and spinal cord. The latter, in turn, receive excitation from the suprasegmental formations of the brain. Thus, the bioelectric potentials taken from the muscle can indirectly reflect changes in the functional state and suprasegmental structures.
In the clinic for electromyography, two methods are used to remove muscle biopotentials - using needle and skin electrodes. With the help of a surface electrode, it is possible to register only the total muscle activity, which represents the interference of action potentials of many hundreds and even thousands of fibers.
Global electromyography muscle biopotentials are removed by skin surface electrodes, which are metal plates or disks with an area of 0.1-1 cm 2, mounted in pairs in fixing pads. Before examination, they are covered with gauze pads moistened with isotonic sodium chloride solution or conductive paste. For fixation, rubber bands or adhesive tape are used. It is customary to record the interference activity of voluntary muscle contraction at a paper tape speed of 5 cm/s. However, with global electromyography using surface electrodes, it is not possible to register fibrillation potentials and it is relatively more difficult to detect fasciculation potentials.
Normal and pathological characteristics of EMG during recording by surface electrodes. In the visual analysis of the global EMG, when it is taken, surface electrodes are used, which give a general description of the EMG curve, determine the frequency of the total electrical activity of the muscles, the maximum amplitude of oscillations, and classify the EMG to one or another type. There are four types of global EMG (according to Yu.S. Yusevich, 1972).
Types of EMG in superficial lead (according to Yu.S. Yusevich, 1972):
1,2-type I; 3, 4 - subtype II A; 5 - subtype II B; 6 - type III, rhythmic fluctuations in tremor; 7 - type III, extrapyramidal rigidity; 8 - type IV, electrical "silence"
- Type I - an interference curve, which is a high-frequency (50 per 1 s) polymorphic activity that occurs during voluntary muscle contraction or when other muscles are strained;
- Type II - rare rhythmic activity (6-50 per 1 s), has two subtypes: Na (6-20 per 1 s) and IIb (21-50 per 1 s);
- Type III - increased frequent oscillations at rest, grouping them into rhythmic discharges, the appearance of flashes of rhythmic and non-rhythmic oscillations against the background of voluntary muscle contraction;
- Type IV electrical "silence" of the muscles during an attempt to voluntary muscle contraction.
Type I EMG is characteristic of normal muscle. During the maximum muscle contraction, the oscillation amplitude reaches 1-2 mV, depending on the strength of the muscle. Type I EMG can be observed not only during voluntary muscle contraction, but also during synergistic muscle tension.
Interference EMG of reduced amplitude is determined in primary muscle lesions. Type II EMG is characteristic of damage to the anterior horns of the spinal cord. Moreover, subtype IIb corresponds to a relatively less severe lesion than subtype Na. EMG subtype IIb is characterized by a greater amplitude of fluctuations, in some cases it reaches 3000-5000 μV. In the case of deep muscle damage, sharper fluctuations of the Ha subtype are noted, often with a reduced amplitude (50-150 μV).
This type of curve is observed when the majority of neurons of the anterior horns are affected and the number of functional muscle fibers.
EMG type II in the initial stages of damage to the anterior horns of the spinal cord may not be detected at rest, with the highest probability, it is masked by interference activity during maximum muscle contraction. In such cases, to identify the pathological process in the muscles, tonic tests (close synergies) are used.
Type III EMG is characteristic of various kinds of supraspinal disorders motor activity. In case of pyramidal spastic paralysis, increased rest activity is recorded on EMG, with parkinsonian tremor, rhythmic bursts of activity are observed, corresponding in frequency to the rhythm of trembling, with hyperkinesis, irregular discharges of activity corresponding to violent movements of the body outside voluntary movements or superimposed on the normal process of muscle voluntary contraction.
EMG type IV indicates complete paralysis of the muscles. In peripheral paralysis, it may be due to complete atrophy of muscle fibers, in acute neuritic lesions, it may indicate a temporary functional block of transmission along the peripheral axon.
During global electromyography, a certain diagnostic interest is caused by the general dynamics of EMG in the process of performing a voluntary movement. So, with supraspinal lesions, one can observe an increase in the time between the order to start the movement and nerve discharges on the EMG. Myotonia is characterized by a significant continuation of EMG activity after the instruction to stop movement, consistent with the known myotonic delay observed clinically.
In myasthenia during maximum muscle effort, there is a rapid decrease in the amplitude and frequency of discharges on the EMG, corresponding to a myasthenic drop in muscle strength during its prolonged tension.
Local electromyography
To register the action potentials (AP) of muscle fibers or their groups, needle electrodes are used, which are inserted into the thickness of the muscle. They may be concentric. These are hollow needles with a diameter of 0.5 mm with an insulated wire inserted inside, a rod made of platinum or stainless steel. Bipolar needle electrodes inside the needle contain two identical metal rods isolated from one another with bare tips. Needle electrodes make it possible to register the potentials of motor units and even individual muscle fibers.
On EMG recorded in this way, it is possible to determine the duration, amplitude, shape and phase of AP. Electromyography using needle electrodes is the main method for diagnosing primary muscular and neuromuscular diseases.
Electrographic characteristics of the state of motor units (MU) in healthy people. PD MU parameters reflect the number, size, relative position and distribution density of muscle fibers in a given MU, its territory, and features of the propagation of potential fluctuations in the volumetric space.
The main parameters of PD DE are amplitude, shape and duration. The PD parameters of the MU differ, since an unequal number of muscle fibers is included in the MU. Therefore, to obtain information about the state of the MU of a given muscle, it is necessary to register at least 20 PD MU and present their average value and distribution histogram. The average duration of PD DE in different muscles in people of different ages is given in special tables.
The duration of PD DE normally varies depending on the muscle and the age of the subject within 5-13 ms, the amplitude is from 200 to 600 μV.
As a result of an increase in the degree of voluntary effort, an increasing number of PDs are activated, which makes it possible to register up to 6 PDs in one position of the retracted electrode. To register other PD DE, the electrode is moved in different directions according to the “cube” method to different depths of the muscle under study.
Pathological phenomena on EMG with needle electrodes. In a healthy person at rest, electrical activity, as a rule, is absent; in pathological conditions, spontaneous activity is recorded. The main forms of spontaneous activity include fibrillation potentials (PF), positive sharp waves (POS) and fasciculation potentials.
a - Pf; b - POV; c - potentials of fasciculations; d - falling AP amplitude during the myotonic discharge (top - the beginning of the discharge, bottom - its end).
Fibrillation potentials are the electrical activity of a single muscle fiber that is not caused by a nerve impulse and recurs. In normal healthy muscle, PF is a typical sign of muscle denervation. They occur most often on the 15-21st day after nerve interruption. The average duration of individual oscillations is 1-2 ms, the amplitude is 50-100 μV.
Positive sharp waves, or positive spikes. Their appearance indicates gross muscle denervation and degeneration of muscle fibers. The average duration of the SOW is 2-15 ms, the amplitude is 100-4000 μV.
The fasciculation potentials have parameters close to those of the PD DE of the same muscle, but they occur during its complete relaxation.
The appearance of PF and SOV indicates a violation of the contact of muscle fibers with the axons of the motor nerves innervating them. This may be due to denervation, long-term impairment of neuromuscular transmission, or mechanical separation of the muscle fiber from that part of it that is in contact with the nerve. PF can also be observed in some metabolic disorders - thyrotoxicosis, metabolic disorders in the mitochondrial apparatus of muscles. Therefore, the identification of PF and POV has no direct relation to the diagnosis. However, monitoring the dynamics of severity and forms of spontaneous activity, as well as comparing spontaneous activity and dynamics of PD MU parameters almost always help to determine the nature of the pathological process.
In cases of denervation in the presence of injuries and inflammatory diseases of the peripheral nerves, a violation of the transmission of nerve impulses is manifested by the disappearance of PD DE. After 2-4 days from the onset of the disease, PF appear. As the denervation progresses, the frequency of detection of PF increases - from single PF in certain areas of the muscle to markedly pronounced, when several PF are recorded anywhere in the muscle. Against the background of a large number of fibrillation potentials, positive sharp waves also appear, the intensity and frequency of which in the discharge increase with the growth of denervation changes in muscle fibers. As the fibers denervate, the number of recorded IFs decreases, while the number and size of SOWs increase, with large-amplitude SOWs predominating. 18–20 months after the nerve dysfunction, only giant SOVs are recorded. In cases where the restoration of nerve function is planned, the severity of spontaneous activity decreases, which is a good prognostic sign preceding the onset of PD DU.
As PD DU increases, spontaneous activity decreases. However, it can be detected many months after clinical recovery. In inflammatory diseases of motor neurons or axons that proceed sluggishly, the first sign of the pathological process is the occurrence of PF, and then SOV, and only much later is a change in the structure of PD DE observed. In such cases, the stage of the denervation process can be assessed by the type of changes in PD and DE, and the severity of the disease can be assessed by the nature of PF and POV.
The appearance of fasciculation potentials indicates changes in the functional state of the motor neuron and indicates its involvement in the pathological process, as well as the level of damage to the spinal cord. Fasciculations can also occur in severe disorders of the axons of the motor nerves.
Stimulation electroneuromyography. Its purpose is to study the evoked responses of the muscle, that is, the electrical phenomena that occur in the muscle as a result of stimulation of the corresponding motor nerve. This makes it possible to investigate a significant number of phenomena in the peripheral neuromotor apparatus, of which the most common are the rate of excitation conduction along the motor nerves and the state of the neuromuscular transmission. To measure the speed of conduction of excitation along the motor nerve, the diverting and stimulating electrodes are placed above the muscle and nerve, respectively. First, the M-response to stimulation is recorded at the proximal point of the nerve. The moments of stimulus supply are synchronized with the launch of the horizontal layout of the oscilloscope, on the vertical plates of which an increased voltage of the AP muscle is applied. Thus, at the beginning of the received record, the moment of stimulus delivery in the form of an irritation artifact is noted, and after a certain period of time, the M-response, which usually has a two-phase negative-positive form, is noted. The interval from the onset of the stimulation artifact to the onset of deviation of the muscle AP from the isoelectric line determines the latent time of the M-response. This time corresponds to conduction along the nerve fibers with the highest conductivity. In addition to recording the latent response time from the proximal nerve stimulation point, the latent response time to stimulation of the same nerve at the distal point is measured and the excitation conduction velocity V is calculated using the formula:
where L is the distance between the centers of the points of application of the active stimulating electrode along the nerve; Tr latent response time in case of stimulation at the proximal point; Td is the latent response time for stimulation at the distal point. The normal speed of conduction along the peripheral nerves is 40-85 m/s.
Significant changes in the speed of conduction are detected in processes that affect the myelin sheath of the nerve, demyelinating polyneuropathies and injuries. This method is of great importance in the diagnosis of so-called tunnel syndromes (consequences (pressure of the nerves in the musculoskeletal channels): carpal, tarsal, cubital, etc.
The study of the speed of excitation is also of great prognostic value during repeated studies.
Analysis of the changes caused by the muscle response to nerve stimulation by series of pulses of different frequencies makes it possible to assess the state of neuromuscular transmission. With supramaximal stimulation of the motor nerve, each stimulus excites all of its fibers, which in turn causes excitation of all muscle fibers.
The amplitude of muscle AP is proportional to the number of excited muscle fibers. Therefore, a decrease in muscle AP reflects a change in the number of fibers that received the appropriate stimulus from the nerve.
It suggests that the neuroactive substance may be formed as a result of treatment with TEPP.
In cockroaches and crayfish, the poisoning of which with DDT has gone so far that it is irreversible, the spontaneous activity of the central nervous system is depressed or almost absent. If the nerve chain of such cockroaches is carefully dissected and washed in saline, then a higher level of spontaneous activity returns to it. In this case, washing removes some
The isoclines of the system at parameters corresponding to the axon membrane are shown in Figs. XXIII.27. The singular point is stable (located on the left branch) and the membrane is not spontaneously active. The level of the resting potential is conventionally taken as zero. As the parameters change, the isoclines deform. If in this case the singular point becomes unstable (shifts from the left branch of the isocline d(f/dt = 0 to the middle one), then spontaneous activity will occur (Fig. XXIII.28.1).
I - spontaneous activity (singular point 8 is unstable, lies on the middle branch) the dotted line shows the projection of the limit cycle of the system onto the plane
It is very interesting that even after the victory of the myogenic theory, the idea of spontaneous activity was alien to many biologists for a long time. They said that any reaction should be a response to some kind of influence, like a reflex. According to them, admitting that muscle cells can contract on their own is like abandoning the principle of causality. They were ready to explain the contraction of heart cells by anything, but not by their own properties (for example, by special fantastic hormones or even by the action of cosmic rays). Our generation still found heated discussions about this.
It was shown above how nerve cells conduct, process and register electrical signals, and then send them to the muscles in order to cause them to contract. But where do these signals come from? There are two spontaneous arousal and sensory stimuli. There are spontaneously active neurons, such as brain neurons, that set the rhythm of breathing. A very complex pattern of spontaneous activity can be generated in a single cell with the help of appropriate combinations of ion channels of the types that we have already met when discussing the mechanisms of information processing by neurons. The reception of sensory information is also based on principles already known to us, but cells of very diverse and surprising types are involved in it.
Individuals with monomorphic a-waves, on average, show themselves to be active, stable and reliable people. Probands are highly likely to show signs of high spontaneous activity and perseverance, accuracy in work, especially under stress, and short-term memory, their strongest qualities. On the other hand, they do not process information very quickly.
toxic concentrations. For animals. Mice. With a two-hour exposure, the minimum concentrations that cause a lateral position are 30-35 mg / l, anesthesia - 35 mg / l, death - 50 mg / l (Lazarev). 17 mg/l cause a large decrease in the spontaneous activity of white mice-C1ey (Geppel et al.). Guinea pigs . 21 mg/l causes
A toxic substance accumulates in the hemolymph of the American cockroach Periplaneta ameri ana L, poisoned with DDT. Chemical analysis showed the absence of significant amounts of DDT in such hemolymph. Injection of DDT-sensitive and resistant cockroaches with hemolymph taken from cockroaches that were in the prostrative phase as a result of DDT poisoning produced the typical symptoms of DDT poisoning. Further, the same hemolymph led to an increase in the spontaneous activity of the nerve chain isolated from an unpoisoned cockroach. After a short period of high arousal, activity suddenly dropped and blockage set in. Since DDT itself does not have a direct effect on the central nervous system, it has been suggested that the above phenomena are caused by some other compound.
If the initial TEPP perfusate, which washed the nerve chain, is poured over the latter again, then spontaneous activity again greatly increases compared to normal, then gradually decreases to a low level, and in some cases blocking occurs. As before, flushing with fresh 10 3 M TEPP solution returns the nerve to its original spontaneous activity.
From cockroaches. The neuroactive substance from the hemolymph of cockroaches in the prostration phase as a result of DDT poisoning was partially isolated by chromatography. After the development of the chromatogram, the active substance was extracted from individual parts of the chromatograms by extraction with saline, after which the effect of the extracts on the spontaneous activity of the cockroach nerve chain was determined. Using various solvents and re-separating the neuroactive fractions by chromatography, we obtained a good separation of the neuroactive substance from various substances present in the hemolymph. Due to the loss of the substance or its biological activity during numerous operations of chromatographic separation, as well as due to the difficulty in obtaining large amounts of cockroach hemolymph, attempts to select compounds for the qualitative recognition of this substance were carried out with only a limited set of compounds, and only one of them gave positive results. Treatment of chromatograms with diazotized p-nitroaniline led to the appearance of red-colored spots at the sites of localization of biologically active substances of the hemolymph extract. On the chromatograms of extracts from the hemolymph of normal cockroaches, red spots did not appear in places corresponding to the Rj of the active substance.
The blood of crayfish poisoned with DDT was treated in the same way as the hemolymph of cockroaches, and it turned out to be neuroactive in experiments with the nervous chain of crayfish and cockroach and caused first excitation, followed by depression of spontaneous activity. Only one difference was noted, the substance from the blood of cancer had a more active effect on the nerves of the cancer than on the nerves
Until now, the discussion has been based on the classical picture of the action of FOS, i.e., it was assumed that FOS affects the nervous system of insects by inhibiting cholinesterase, which in turn leads to impaired function of acetylcholine. A study by Sternburg et al. cast doubt on the validity of this assumption. They took an isolated american cockroach strand and placed it in a saline solution and observed high spontaneous activity. This fluid was then replaced with 10 M TEPP in saline and, as expected, a rapid and complete blockade occurred. The mixture of TEPP with saline was temporarily removed, let's call this mixture m. After that, the preparation was washed several times with freshly prepared mixture of TEPP with saline, as a result of which normal spontaneous activity was restored. If the preparation was then again treated with a mixture of T, excitation followed by blockade was observed.
The computer-calculated null-isoclines are shown in Figs. XXIII.27. The isocline d(f/dt = O has an N-shape, which ensures the generation of an impulse . The singular point is located on the left branch of the isocline d(f/dt = O and is stable. This corresponds to the absence of spontaneous activity in the original Hodgkin-Huxley equations.
However, about a hundred years ago, the English physiologist Gaskell seriously criticized this theory and put forward a number of arguments in favor of the fact that the muscle cells of some parts of the heart themselves are capable of spontaneous rhythmic activity (myogenic theory). For more than half a century there was a fruitful scientific discussion, which eventually led to the victory of the myogenic theory. It turned out that in the heart there really are two areas of special muscle tissue, the cells of which have spontaneous activity. One site is located in the right atrium (it is called the sino-atrial node), the other is on the border of the atrium and ventricle (the so-called atrioventricular node). The first has a more frequent rhythm and determines the work of the heart under normal conditions (then they say that the heart has a sinus rhythm), the second is a spare if the first node stops, then after a while the second section starts to work and the heart starts to beat again, although in a rarer rhythm. If you isolate individual muscle cells from one or another area and place them in a nutrient medium, then these cells continue to contract in their characteristic sinus rhythm - more often, atrio-ventricular - less often.
We said that retinal rods respond to excitation of just one molecule of rhodopsin. But such excitation can arise not only under the action of light, but also under the action of thermal noise. As a result of the high sensitivity of the rods, false alarms should occur all the time in the retina. However, in reality, the retina also has a noise control system based on the same principle. The rods are interconnected by ES, which leads to averaging of their potential shifts, so that everything happens the same way as in electroreceptors (only there the signal is averaged in the fiber that receives signals from many receptors, and in the retina - right in the receptor system). Also remember the association through highly permeable contacts of spontaneously active cells of the sinus node of the heart, which gives a regular heart rate and eliminates the fluctuations inherent in a single cell (noise). We see that nature
JOURNAL OF HIGHER NERVOUS ACTIVITY, 2010, volume 60, no. 4, p. 387-396
REVIEWS, THEORETICAL ARTICLES
UDC 612.822.3
SPONTANEOUS ACTIVITY IN DEVELOPING NEURAL NETWORKS
M. G. Sheroziya and A. V. Egorov
Institution of the Russian Academy of Sciences Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow,
e-mail: [email protected] Received September 7, 2009; accepted for publication October 26, 2009
Spontaneous activity is a hallmark of the developing nervous system. It is assumed that spontaneous activity plays a key role in the formation of a neural network and the maturation of neurons. The most intense spontaneous activity of neurons was studied in the hippocampus, cerebral cortex, retina and spinal cord in embryos and newborn animals. The article provides an overview of the main results of studies of spontaneous activity in the developing nervous system and discusses possible mechanisms for its generation.
Key words: development, hippocampus, cortex, retina, spinal cord, spontaneous network activity.
Spontaneous Network Activity of the Developing Nervous System
M. G. Sheroziya, A. V. Egorov
Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow,
e-mail: [email protected]
A review. Spontaneous periodic network activity is a characteristic feature of the developing nervous system. It is believed that early spontaneous activity is involved in the modulation of several processes during brain maturation, including neuronal growth and network construction. Periodic spontaneous network activity was observed and studied in detail in hippocampus, cortex, retina and spinal cord of embryos and newborn animals. Principal studies of spontaneous network activity in the developing nervous system are reviewed, and possible mechanisms of its generation are discussed.
Key words: development, hippocampus, cortex, retina, spinal cord, spontaneous network activity.
Spontaneous activity is a hallmark of the developing nervous system. It is assumed that spontaneous activity plays a key role in the formation of a neural network and the maturation of neurons. Spontaneous activity is already observed in neural progenitors. Typically, such activity is recorded as fluctuations in the concentration of intracellular calcium or calcium spikes. With the formation of the first contacts between neurons of electrical synapses, synchronized spontaneous activity appears. Further, with the development of chemical synapses in ontogeny, new types of synchronous spontaneous activity appear. Since the advent of chemical synapses, the synchronous activity of neurons can be considered networked in the usual sense of the word. The network spontaneous activity of neurons during embryonic and postnatal development has been intensively studied in many structures of the central nervous system of vertebrates, especially in the hippocampus, cerebral cortex, retina, and spinal cord.
THE HIPPOCAMPUS AND THE NEW CORTEX
The first ontogenesis synchronous activity of groups of neurons in the hippocampus of mice appears a few days before birth
Small ensembles of neurons in sections of the hippocampus synchronously generate bursts of spikes, which is accompanied by an increase in intracellular calcium. This first synchronous activity of small groups of neurons was called "synchronous plateau assemblies" (SPA) by the authors. SPA activity was generated due to electrical contacts between neurons, since SPA activity disappeared under the action of blockers of electrical synapses. The peak of SPA activity occurred at the time of birth, and by the end of the second week of life, this type of spontaneous activity disappeared. The same group of researchers found similar electrical synapse-related SPA activity in the cerebral cortex of newborn rats. Previously, other authors in newborn animals showed the synchronization of neuronal domains dependent on electrical contacts between neurons, which then, presumably, develop into cortical columns. The synchronous activity of large groups of neurons, dependent on electrical synapses, has also been shown in specially prepared thick sections of the cortex of newborn animals. The connection between such synchronization and SPA activity remains unclear. Perhaps SPA activity represents an earlier form of such synchronization.
With the development of chemical synapses, other types of synchronous spontaneous activity appear. Probably the best known type of spontaneous activity in newborn animals is the so-called giant depolarizing potentials (GDP), first shown in sections of the rat hippocampus. GDPs were recorded intracellularly and were bursts of spikes approximately 0.3 s long, following at a frequency of approximately 0.1 Hz. Along with antagonists of glutamate synaptic transmission, GDP was blocked or suppressed by the action of picrotoxin and bicuculline. Thus, it was shown important role GABAergic system in GDP generation and for the first time discovered an unusual excitatory effect of GABA in the hippocampus of newborn animals. GDP was observed in most of the pyramidal cells of the hippocampus of newborn rats and completely disappeared by the end of the second week of life. The peak of GDP activity in the hippocampus is
born animals accounted for 7-10 days of life. Although SPA activity appears earlier in ontogeny than GDP, according to the work from the 2nd day of life (approximate time of GDP appearance), GDP and SPA activities coexist in the hippocampus and are in antiphase to each other, i.e. an increase in GDP leads to a decrease in SPA activity, and vice versa. When GDP was blocked by antagonists of synaptic transmission, hippocampal slice cells generated SPA activity.
Spontaneous GDP activity with similar properties has also been found in the cerebral cortex of newborn rats. Interestingly, however, another type of spontaneous activity associated with chemical synapses, called "early network oscillations" (ENOs), was previously recorded in the cortex. No such activity was observed in the hippocampus. ENOs were periodic synchronous changes in intracellular calcium concentration in small groups of neurons. On horizontal sections of the brain, ENOs activity propagated along the cortex as a wave at a speed of 2 mm/s. ENOs activity disappeared by the 5-7th day of life, and the peak occurred at the time of birth. ENOs activity disappeared under the influence of already low concentrations of AMPA/kainate receptor blockers. Thus, in the cortex, in contrast to the hippocampus, spontaneous glutamate-dependent ENOs activity appeared during development earlier than GDP, the generation of which many researchers explain by the excitatory action of GABA.
The transition in ontogeny from electrical to chemical synapses during the generation of spontaneous activity has also been shown for induced oscillations. Thus, spontaneous oscillations induced by carbachol (an agonist of muscarinic receptors) on sections of the cortex in newborn and week-old animals depended on electrical and chemical synapses, respectively.
The ability of hippocampal and cortical neurons to generate GABA-dependent GDP can be associated with the sequential development of the GABA- and glutamatergic systems of the brain. According to a number of works, the GABAergic system is formed earlier than the glutamate one: GABAergic interneurons mature before glutamate pyramidal cells, interneurons
The rons are also the source and target of the formation of the first synapses. Initially, GABAergic synapses are excitatory, which is associated with a high (up to 40 mM) intracellular concentration of chloride ions compared to the usual concentration in adults (approximately 7 mM). If in adults the activation of GABAergic synapses leads to the entry of negatively charged chloride ions into the cell and, thus, to membrane hyperpolarization, then in newborns the opposite occurs - the release of chloride ions and depolarization of the membrane. As glutamate synapses form with age, GABAergic synapses gradually turn into inhibitory synapses. It is assumed that this is how the balance between excitation and inhibition in the developing brain is maintained. The ability of cortical and hippocampal neurons to generate GABA-dependent GDP over time correlates approximately with the depolarizing action of GABA.
The high content of chloride ions in the intracellular fluid of the neurons of newborn animals is associated with different time expression of the two main chloride co-transporters. The co-transporter NKCC1 pumping chlorine into the cell is expressed before the chlorine pumping KCC2. Interestingly, the expression of KCC2 and, accordingly, the time during which GABA will remain depolarizing, depends on the spontaneous activity of cells. Thus, it was shown in cultures of neurons that chronic blocking of GABA receptors prevents the expression of KCC2, while the concentration of intracellular chlorine does not decrease and GABA remains a depolarizing mediator. Blocking of glutamate receptors or fast sodium channels did not lead to changes in KCC2 expression. Thus, it has been proven that spontaneous miniature GABAergic postsynaptic currents (PSCs) are required for KCC2 expression, decrease in intracellular chlorine concentration, and conversion of GABA into an inhibitory mediator.
However, direct evidence of the need for network spontaneous activity, such as GDP, for the formation of a neural network in the cortex and hippocampus is not yet available, although such assumptions have been made. The peak of GDP activity in rats falls at the end of
howl, the beginning of the second week of life. The main connections by this time have already been partially established, for example, the perforating pathway and synapses of mossy fibers in the hippocampus of rats begin to form even before birth. Sectional experiments have shown that GDPs are able to induce long-term potentiation in the emerging "silent" synapses of the neonatal rat hippocampus. called so
For further reading of the article, you must purchase the full text. Articles are sent in the format PDF to the email address provided during payment. Delivery time is less than 10 minutes ZHURAVLEVA Z.N. - 2004
Needle EMG includes the following main techniques:
- standard needle EMG;
- EMG of a single muscle fiber;
- macroEMG;
- scanning EMG.
Standard needle electromyography
Needle EMG is an invasive research method carried out using a concentric needle electrode inserted into the muscle. Needle EMG makes it possible to evaluate the peripheral neuromotor apparatus: the morphofunctional organization of the MU of skeletal muscles, the state of muscle fibers (their spontaneous activity), and with dynamic observation, to evaluate the effectiveness of treatment, the dynamics of the pathological process and the prognosis of the disease.
INDICATIONS
Diseases of the motor neurons of the spinal cord (ALS, spinal amyotrophies, poliomyelitis and post-poliomyelitis syndrome, syringomyelia, etc.), myelopathy, radiculopathy, various neuropathies (axonal and demyelinating), myopathies, inflammatory muscle diseases (polymyositis and dermatomyositis), central movement disorders, sphincter disorders and a number of other situations when it is necessary to objectify the state of motor functions and the movement control system, to assess the involvement of various structures of the peripheral neuromotor apparatus in the process.
CONTRAINDICATIONS
There are practically no contraindications for needle EMG. The limitation is the unconscious state of the patient, when he cannot voluntarily strain the muscle. However, even in this case it is possible to determine the presence or absence of the current process in the muscles (by the presence or absence of spontaneous activity of muscle fibers). With caution, needle EMG should be performed in those muscles in which there are pronounced purulent wounds, non-healing ulcers and deep burn lesions.
DIAGNOSTIC VALUE
Standard needle EMG occupies a central place among electrophysiological research methods for various neuromuscular diseases and is of decisive importance in the differential diagnosis of neurogenic and primary muscular diseases.
Using this method, the severity of denervation in the muscle innervated by the affected nerve, the degree of its recovery, and the effectiveness of reinnervation are determined.
Needle EMG has found its application not only in neurology, but also in rheumatology, endocrinology, sports and professional medicine, pediatrics, urology, gynecology, surgery and neurosurgery, ophthalmology, dentistry and maxillofacial surgery, orthopedics and a number of other medical fields.
PREPARATION FOR THE STUDY
Special preparation of the patient for the study is not necessary. Needle EMG requires complete relaxation of the examined muscles, so it is performed with the patient lying down. The patient is exposed to the examined muscles, laid on his back (or stomach) on a comfortable soft couch with an adjustable headrest, informed about the upcoming examination and explained how he should strain and then relax the muscle.
METHODOLOGY
The study is carried out using a concentric needle electrode inserted into the motor point of the muscle (the permissible radius is no more than 1 cm for large muscles and 0.5 cm for small ones). Register potentials DE (PDE). When choosing a PDE for analysis, it is necessary to follow certain rules for their selection.
Reusable needle electrodes are pre-sterilized in an autoclave or other sterilization methods. Disposable sterile needle electrodes are opened immediately before muscle examination.
After inserting the electrode into a completely relaxed muscle and each time it is moved, the possible occurrence of spontaneous activity is monitored.
Registration of PDEs is carried out at a minimum voluntary muscle tension, which makes it possible to identify individual PDEs. 20 different PDEs are selected, following a certain sequence of electrode movement in the muscle.
When assessing the state of the muscle, a quantitative analysis of detected spontaneous activity is carried out, which is especially important when monitoring the patient's condition in dynamics, as well as in determining the effectiveness of therapy. Analyze the parameters of the registered potentials of various DE.
INTERPRETATION OF THE RESULTS
DE is a structural and functional element of skeletal muscle. It is formed by a motor motor neuron located in the anterior horn of the gray matter of the spinal cord, its axon, which emerges in the form of a myelinated nerve fiber as part of the motor root, and a group of muscle fibers that, using a synapse, form contact with numerous branches of this axon, which are devoid of a myelin sheath - terminals (Fig. .8-8).
Each muscle fiber of a muscle has its own terminal, is part of only one MU and has its own synapse. Axons begin to branch intensively at the level of several centimeters to the muscle in order to provide innervation to each muscle fiber that is part of this MU. The motor neuron generates a nerve impulse that is transmitted along the axon, amplified in the synapse and causes the contraction of all muscle fibers belonging to this MU. The total bioelectric potential recorded during such a contraction of muscle fibers is called the potential of the motor unit.
Rice. 8-8. Schematic representation of DE.
Motor unit potentials
Judgment on the state of DE of human skeletal muscles is obtained on the basis of an analysis of the parameters of the potentials generated by them: duration, amplitude and shape. Each PDE is formed as a result of the algebraic addition of the potentials of all muscle fibers that make up the DE, which functions as a whole.
When the excitation wave propagates along the muscle fibers towards the electrode, a three-phase potential appears on the monitor screen: the first deviation is positive, then there is a fast negative peak, and the potential ends with the third, again positive deviation. These phases can have different amplitudes, durations, and areas, depending on how the electrode outlet surface is located relative to the central part of the recorded DE.
PDE parameters reflect the size of the MU, the number, relative position of muscle fibers and the density of their distribution in each specific MU.
Duration of motor unit potentials is normal
The main parameter of the PDE is its duration, or duration, measured as the time in milliseconds from the beginning of the signal's deviation from the center line to its complete return (Fig. 8-9).
The duration of PDE in a healthy person depends on the muscle and age. With age, the duration of PDE increases. In order to create unified criteria for the norm in the study of PDE, special tables of normal average durations for different muscles of people of different ages have been developed.
A fragment of such tables is given below (Table 8-5).
A measure for assessing the state of MU in a muscle is the average duration of 20 different PMUs recorded at different points of the muscle under study. The average value obtained during the study is compared with the corresponding indicator presented in the table, and the deviation from the norm is calculated (in percent). The average duration of the PDE is considered normal if it falls within the limits of ± l2% of the value given in the table (abroad, the average duration of the PDE is considered normal if it falls within the limits of ± 20%).
Rice. 8-9. Measurement of PDE duration.
Table 8-5. Average duration in PMU in the most frequently studied muscles of healthy people, ms
| Age, years | M. del to-ideus | M.extensordigiti comm. | M.abductor pollicisbrevis | M.interosseusdorsal is | M. abductor digiti minimi manus | M. vastus l ateral is | M. tibialisanterior | M. gastro-cnemius |
| 0 | 7,6 | 7,1 | 6,2 | 7,2 | b,2 | 7,9 | 7,5 | 7,2 |
| 3 | 8,1 | 7,6 | 6,8 | 7,7 | b,8 | 8,4 | 8,2 | 7,7 |
| 5 | 8,4 | 7,8 | 7,3 | 7,9 | 7,3 | 8,7 | 8,5 | 8,0 |
| 8 | 8,8 | 8,2 | 7,9 | 8,3 | 7,9 | 9,0 | 8,7 | 8,4 |
| 10 | 9,0 | 8,4 | 8,3 | 8,7 | 8,3 | 9,3 | 9,0 | 8,6 |
| 13 | 9,3 | 8,7 | 8,7 | 9.0 | 8,7 | 9,6 | 9,4 | 8,8 |
| 15 | 9,5 | 8,8 | 9,0 | 9,2 | 9,0 | 9,8 | 9,6 | 8,9 |
| 1 8 | 9,7 | 9,0 | 9,2 | 9,4 | 9,2 | 10,1 | 9,9 | 9,2 |
| 20 | 10,0 | 9,2 | 9,2 | 9,6 | 9,2 | 10,2 | 10,0 | 9,4 |
| 25 | 10,2 | 9,5 | 9,2 | 9,7 | 9,2 | 10,8 | 10,6 | 9,7 |
| 30 | 10,4 | 9,8 | 9,3 | 9,8 | 9,3 | 11,0 | 10,8 | 10,0 |
| 35 | 10,8 | 10,0 | 9,3 | 9,9 | 9,3 | 11,2 | 11,0 | 10,2 |
| 40 | 11,0 | 10,2 | 9,3 | 10,0 | 9,3 | 11,4 | 11, 2 | 10,4 |
| 45 | 11,1 | 10,3 | 9,4 | 10,0 | 9,4 | 11,5 | 11,3 | 10,5 |
| 50 | 11,3 | 10,5 | 9,4 | 10,0 | 9,4 | 11,7 | 11,5 | 10,7 |
| 55 | 11,5 | 10,7 | 9,4 | 10,2 | 9,4 | 11,9 | 11,7 | 10,9 |
| 60 | 11,8 | 11,0 | 9,5 | 10,3 | 9,5 | 12,2 | 12,0 | 11,2 |
| 65 | 12,1 | 11,2 | 9,5 | 10,3 | 9,5 | 12,4 | 12,2 | 11,5 |
| 70 | 12,3 | 11,4 | 9,5 | 10,4 | 9,5 | 12,6 | 12,4 | 11,7 |
| 75 | 12,5 | 11,6 | 9,5 | 10,5 | 9,5 | 12,7 | 12,5 | 11,8 |
| 80 | 12,6 | 11,8 | 9,5 | 10,6 | 9,5 | 12,8 | 12,6 | 12,0 |
Duration of potentials of motor units in pathology
The main pattern of changes in the duration of PDE in pathological conditions is that it increases with neurogenic diseases and decreases with synaptic and primary muscular pathology.
In order to more carefully assess the degree of change in PMU in muscles with various lesions of the peripheral neuromotor apparatus, a histogram of the distribution of PMU by duration is used for each muscle, since their average value may be within the limits of normal deviations with obvious muscle pathology. Normally, the histogram has the form of a normal distribution, the maximum of which coincides with the average duration of the PDE for a given muscle.
With any pathology of the peripheral neuromotor apparatus, the shape of the histogram changes significantly.
Electromyographic stages of the pathological process
Based on the change in the duration of PDE in diseases of the motor neurons of the spinal cord, when all the changes occurring in the muscles can be traced in a relatively short period of time, six EMG stages have been identified, reflecting the general patterns of restructuring of the DE during the denervation-reinnervation process (DRP), from the very beginning of the disease to practically complete death of the muscle [Gecht B.M. et al., 1997].
In all neurogenic diseases, more or less motor neurons or their axons die. The surviving motor neurons innervate "alien" muscle fibers deprived of nervous control, thereby increasing their number in their own MUs. On EMG, this process manifests itself as a gradual increase in the parameters of the potentials of such DUs. The entire cycle of changes in the histogram of the PDE distribution by duration in neuronal diseases conditionally fits into five EMG stages (Fig. 8-10), reflecting the process of compensatory innervation in the muscles. Although such a division is conditional, it helps to understand and trace all the stages of the development of DRP in each specific muscle, since each stage reflects a certain phase of reinnervation and its degree of severity. It is inappropriate to represent stage VI as a histogram, since it reflects the end point of the "reverse" process, that is, the process of decompensation and destruction of the MU muscle.
Rice. 8-10. Five stages of DRP in the deltoid muscle of a patient with ALS during a long-term follow-up. H (normal) - 20 PDEs and a histogram of their distribution by duration in the deltoid muscle of a healthy person; I , II , IIIA, IIIB, IV, V - PDE and histograms of their distribution in the corresponding EMG stage. The abscissa shows the duration of PDEs, the ordinate shows the number of PDEs of a given duration. Solid lines - the limits of the norm, dashed lines - the average duration of the PDE in the norm, the arrows indicate the average duration of the PDE in this muscle of the patient at different periods of the examination (successively from I to V stages). Scale: vertical 500 μV, horizontal 10 ms.
Among the specialists of our country, these stages are widely used in the diagnosis of various neuromuscular diseases. They are included in the computer program of domestic electromyographs, which allows automatic construction of histograms with the designation of the process stage.
A change in the stage in one direction or another during the re-examination of the patient shows what are the further prospects for the development of DR.
Stage 1: the average duration of PDE is reduced by 13-20%. This stage reflects the very initial phase of the disease, when denervation has already begun, and the process of reinnervation is not yet manifested electromyographically. Some of the denervated muscle fibers, devoid of impulse influence due to the pathology of either the motor neuron or its axon, fall out of the composition of some MUs. The number of muscle fibers in such MUs decreases, which leads to a decrease in the duration of individual potentials.
In stage I, a certain number of potentials appear narrower than in a healthy muscle, which causes a slight decrease in the average duration.
The histogram of the PDE distribution begins to shift to the left, towards smaller values.
Stage 2: the average duration of PDE is reduced by 21% or more. With ADR, this stage is noted extremely rarely and only in those cases when, for some reason, reinnervation does not occur or is suppressed by some factor (for example, alcohol, radiation, etc.), and denervation, on the contrary, increases and massive death of muscle fibers in DE. THIS leads to the fact that most or almost all PDUs become shorter than normal in duration, and therefore the average duration continues to decrease.
The histogram of the PDE distribution is significantly shifted towards smaller values. I - II stages reflect changes in MU, due to a decrease in the number of functioning muscle fibers in them.
Stage 3: the average duration of PDE is within ± 20% of the norm for this muscle. This stage is characterized by the appearance of a certain number of potentials of increased duration, which are not normally detected.
The appearance of these PMUs indicates the beginning of reinnervation, that is, denervated muscle fibers begin to be included in other MUs, and therefore the parameters of their potentials increase. PDEs of both reduced and normal, and increased duration are simultaneously recorded in the muscle, the number of enlarged PDEs in the muscle varies from one to several. The average duration of PDE in the 1st stage may be normal, but the appearance of the histogram differs from the norm. It does not have the form of a normal distribution, but is "flattened", stretched and begins to shift to the right, towards larger values. It is proposed to divide the PI stage into two subgroups - III A and III B. They differ only in that at the IPA stage, the average duration of the PDE is reduced by 1-20%, and at the stage of the IPB, it either completely coincides with the average value of the norm, or is increased by 1 -20%. In stage III B, several large quantity PDE of increased duration than at stage III A. Practice has shown that such a division of the third stage into two subgroups is not of particular importance. In fact, stage III simply means the appearance of the first EMG signs of reinnervation in the muscle.
Stage IV: the average duration of PDE is increased by 21-40%. This stage is characterized by an increase in the average duration of PDEs due to the appearance, along with normal PDEs, of a large number of potentials of increased duration. PDE of reduced duration at this stage is recorded extremely rarely. The histogram is shifted to the right, towards large values, its shape is different and depends on the ratio of PDEs of normal and increased duration.
Stage V: the average duration of PDE is increased by 41% or more. This stage is characterized by the presence of predominantly large and "giant" PMUs, and PMUs of normal duration are practically absent. The histogram is significantly shifted to the right, stretched and, as a rule, open. This stage reflects the maximum amount of reinnervation in the muscle, as well as its efficiency: the more giant PDEs, the more effective reinnervation.
Stage VI: the average duration of PDE is within the normal range or reduced by more than 12%. This stage is characterized by the presence of PDEs changed in shape (potentials of collapsing DUs). Their parameters can formally be normal or reduced, but the shape of the PDE is changed: the potentials do not have sharp peaks, they are stretched, rounded, the rise time of the potentials is sharply increased. This stage is noted at the last stage of DR decompensation, when most of the motor neurons of the spinal cord have already died and the rest are intensively dying. Decompensation of the process begins from the moment when the process of denervation increases, and the sources of innervation become less and less. On EMG, the stage of decompensation is characterized by the following signs: PDE parameters begin to decrease, giant PDEs gradually disappear, PF intensity increases sharply, giant SOVs appear, which indicates the death of many nearby muscle fibers. These signs indicate that in this muscle the motor neurons have exhausted their ability to sprouting as a result of functional inferiority and are no longer able to exercise full control over their fibers. As a result, the number of muscle fibers in the MU is progressively reduced, the mechanisms of impulse conduction are disrupted, the potentials of such MU are rounded, their amplitude decreases, and the duration decreases. The construction of a histogram at this stage of the process is inappropriate, since it, like the average duration of the PDE, no longer reflects the true state of the muscle. The main symptom of stage VI is a change in the shape of all PDEs.
EMG stages are used not only for neurogenic, but also for various primary muscle diseases, in order to characterize the depth of muscle pathology. In this case, the EMG stage does not reflect the DRP, but the severity of the pathology and is called the "EMG stage of the pathological process". In primary muscular dystrophies, sharply polyphasic PDEs can appear with satellites that increase their duration, which significantly increases its average value, corresponding to the 3rd or even IV EMG stage of the pathological process.
Diagnostic significance of EMG stages.
In neuronal diseases in the same patient in different muscles often detect different EMG stages - from III to V. Stage 1 is detected very rarely - at the very beginning of the disease, and only in individual muscles.
In axonal and demyelinating diseases, III and IV are more often detected, less often - stages 1 and II. With the death of a significant number of axons in some of the most affected muscles, stage V is detected.
In primary muscle diseases, there is a loss of muscle fibers from the MU due to any pathology of the muscle: a decrease in the diameter of the muscle fibers, their splitting, fragmentation or other damage to them, which reduces the number of muscle fibers in the MU or reduces the volume of the muscle. All this leads to a decrease (shortening) of the PDE duration. Therefore, in most primary muscular diseases and myasthenia gravis, stages 1 and 11 are detected, with polymyositis, only 1 and 2 at first, and with recovery, stages 3 and even IV.
Amplitude of motor unit potentials
Amplitude is an auxiliary, but very important parameter in the analysis of PDE. It is measured "peak to peak", that is, from the lowest point of a positive peak to the highest point of a negative peak. When PDEs are registered on the screen, their amplitude is determined automatically. Both the average and the maximum PDE amplitude detected in the studied muscle are determined.
The average PDE amplitude in the proximal muscles of healthy people in most cases is 500-600 μV, in the distal - 600-800 μV, while the maximum amplitude does not exceed 1500-1700 μV. These indicators are very conditional and may vary to some extent. In children 8-12 years old, the average PDE amplitude, as a rule, is in the range of 300-400 μV, and the maximum does not exceed 800 μV; In older children, these figures are 500 and 1000 microvolts, respectively. In the muscles of the face, the PDE amplitude is much lower.
Athletes in trained muscles register an increased amplitude of PDE. Therefore, an increase in the average amplitude of the PDE in the muscles of healthy individuals involved in sports cannot be considered a pathology, since it occurs as a result of the restructuring of the PDE due to a prolonged load on the muscles.
In all neurogenic diseases, the amplitude of PDE, as a rule, increases in accordance with the increase in duration: the longer the duration of the potential, the higher its amplitude (Fig. 8-11).
Rice. 8-11 . Amplitude of PDEs differing in duration.
The most significant increase in PDE amplitude is observed in neuronal diseases such as spinal amyotrophy and the consequences of poliomyelitis.
It serves as an additional criterion for diagnosing the neurogenic nature of the pathology in the muscles. An increase in the amplitude of the PDE leads to a restructuring of the DE in the muscle, an increase in the number of muscle fibers in the electrode lead zone, synchronization of their activity, and an increase in the diameter of the muscle fibers.
An increase in both the average and maximum PDE amplitude is sometimes observed in some primary muscular diseases, such as polymyositis, primary muscular dystrophy, dystrophic myotonia, etc.
Form of motor unit potentials
The shape of the PDE depends on the structure of the DU, the degree of synchronization of the potentials of its muscle fibers, the position of the electrode in relation to the muscle fibers of the analyzed DU and their innervation zones. The shape of the potential has no diagnostic value.
A - PDE of low amplitude and reduced duration, registered with myopathy; B - PDE of normal amplitude and duration, noted in a healthy person; C - PDE of high amplitude and increased duration in polyneuropathy; D - giant PDE (does not fit on the screen), recorded during spinal amyotrophy (amplitude - 1 2 752 μV, duration - more than 35 ms). Resolution 200 µV/d, sweep 1 ms/d.
Rice. 8-12. Polyphasic (A - 5 crossings, 6 phases) and pseudo-polyphasic (5 - 2 crossings, 3 phases and 9 turns, 7 of them in the negative part of the potential) PDE.
In clinical practice, the form of PDE is analyzed in terms of the number of phases and/or turns in the potential. Each positive-negative potential deviation that reaches the isoline and crosses it is called a phase, and a positive-negative potential deviation that does not reach the isoline is called a turn.
A polyphase potential is one that has five or more phases and crosses the center line at least four times(Fig. 8-12, A). There may be additional turns in the potential that do not cross the center line (Fig. 8-12, B). Turns are both in the negative and in the positive part of the potential.
In the muscles of healthy people, the PDE, as a rule, is represented by three-phase potential oscillations (see Fig. 8-9), however, when registering the PDE in the end plate zone, it can have two phases, losing its initial positive part.
Normally, the number of polyphasic PDEs does not exceed 5-15%. An increase in the number of polyphasic PDEs is considered as a sign of a violation of the DU structure due to the presence of some pathological process. Polyphasic and pseudopolyphasic PDEs are recorded both in neuronal and axonal, and in primary muscle diseases (Fig. 8-13).
Rice. 8-13. Sharply polyphasic PDE (21 phases), registered in a patient with progressive muscular dystrophy. Resolution 100 µV/d, sweep 2 ms/d. PDE amplitude 858 μV, duration 19.9 ms.
Spontaneous activity
Under normal conditions, when the electrode is stationary in a relaxed muscle of a healthy person, no electrical activity occurs. With pathology, spontaneous activity of muscle fibers or MU appears.
Spontaneous activity does not depend on the will of the patient, he cannot stop it or cause it arbitrarily.
Spontaneous activity of muscle fibers
The spontaneous activity of muscle fibers includes fibrillation potentials (PF) and positive sharp waves (pav). PF and POV are recorded exclusively in pathological conditions when a concentric needle electrode is inserted into the muscle (Fig. 8-14). PF is the potential of one muscle fiber, POV is a slow oscillation following a fast positive deviation without a sharp negative peak. SOV reflects the participation of both one and several adjacent fibers.
Rice. 8-14. Spontaneous activity of muscle fibers. A - fibrillation potentials; B - positive sharp waves.
The study of spontaneous activity of muscle fibers in the conditions of a clinical study of a patient is the most convenient electrophysiological method that allows one to judge the degree of usefulness and stability of nerve influences on muscle fibers of a skeletal muscle in its pathology.
Spontaneous activity of muscle fibers can occur in any pathology of the peripheral neuromotor apparatus. In neurogenic diseases, as well as in the pathology of the synapse (myasthenia and myasthenic syndromes), the spontaneous activity of muscle fibers reflects the process of their denervation. In most primary muscle diseases, the spontaneous activity of muscle fibers reflects any damage to the muscle fibers (their splitting, fragmentation, etc.), as well as their pathology caused by the inflammatory process (in inflammatory myopathies - polymyositis, dermatomyositis).
In both cases, PF and POV indicate the presence of a current process in the muscle; normally they are never recorded.
The duration of the PF is 1-5 ms (it does not have any diagnostic value), and the amplitude varies over a very wide range (on average 118 ± 1 14 μV). Sometimes high-amplitude (up to 2000 µV) PF are also found, usually in patients with chronic diseases. The timing of the appearance of PF depends on the location of the nerve lesion. In most cases, they occur 7-20 days after denervation.
If for some reason the reinnervation of the denervated muscle fiber did not occur, it eventually dies, generating surfactants, which consider EMG a sign of the death of the denervated muscle fiber that has not received the innervation it lost earlier. By the number of PF and SOV recorded in each muscle, one can indirectly judge the degree and depth of its denervation or the volume of dead muscle fibers. The duration of the SOV is from 1.5 to 70 ms (in most cases up to 10 ms). The so-called giant POVs lasting more than 20 ms are detected with prolonged denervation of a large number of adjacent muscle fibers, as well as with polymyositis. The SOW amplitude usually ranges from 10 to 1800 μV. SOVs of large amplitude and duration are more often detected in the later stages of denervation (giant SOVs). SOV begin to register 16-30 days after the first appearance of PF, they can persist in the muscle for several years after denervation.
As a rule, in patients with inflammatory lesions of the peripheral nerves, POV is detected later than in patients with traumatic lesions. PF and POV most quickly respond to the start of therapy: if it is effective, the severity of PF and POV decreases after 2 weeks. On the contrary, if the treatment is ineffective or insufficiently effective, their severity increases, which makes it possible to use the analysis of PF and SOV as an indicator of the effectiveness of the drugs used.
Myotonic and pseudomyotonic shocks
Myotonic and pseudomyotonic discharges, or high frequency discharges, also refer to the spontaneous activity of muscle fibers. Myotonic and pseudomyotonic discharges are distinguished by a number of features, the main of which is the high repeatability of the elements that make up the discharge, that is, the high frequency of potentials in the discharge. The term "pseudomyotonic shock" is increasingly being replaced by the term "high frequency shock".
Myotonic discharges are a phenomenon found in patients with various forms of myotonia. When listening, it resembles the sound of a "dive bomber". On the monitor screen, these discharges look like repeating potentials of gradually decreasing amplitude, with progressively increasing intervals (which causes a decrease in pitch, Fig. 8-15). Myotonic discharges are sometimes observed in some forms of endocrine pathology (for example, hypothyroidism). Myotonic discharges occur either spontaneously or after a slight contraction or mechanical stimulation of the muscle by a needle electrode inserted into it or by simple tapping on the muscle.
Pseudomyotonic discharges (high frequency discharges) are recorded in some neuromuscular diseases, both associated and not associated with denervation of muscle fibers (Fig. 8-16). They are considered a consequence of the ephaptic transfer of excitation with a decrease in the insulating properties of the membrane of muscle fibers, creating a prerequisite for the spread of excitation from one fiber to the adjacent one: the pacemaker of one of the fibers sets the rhythm of the impulse, which is imposed on the adjacent fibers, which is the reason for the peculiar form of the complexes. Discharges begin and stop suddenly. Their main difference from myotonic discharges is the absence of a drop in the amplitude of the components. Pseudomyotonic discharges are observed in various forms of myopathy, polymyositis, denervation syndromes (in the late stages of reinnervation), spinal and neural amyotrophies (Charcot-Marie-Tous disease), endocrine pathology, trauma or nerve compression, and some other diseases.
Rice. 8-15. Myotonic discharge registered in the anterior tibial muscle of a patient (19 years old) with Thomsen's myotonia. Resolution 200 µB/d.
Rice. 8-16. A high-frequency discharge (pseudomyotonic discharge) recorded in the anterior tibial muscle of a patient (32 years old) with neural amyotrophy (Charcot-Marie-Tooth disease) type IA. The discharge stops suddenly, without a preliminary drop in the amplitude of its components. Resolution 200 µV/d.
Spontaneous activity of motor units
Spontaneous DE activity is represented by fasciculation potentials. Fasciculations are called spontaneous contractions of the entire MU that occur in a completely relaxed muscle. Their occurrence is associated with diseases of the motor neuron, its overload with muscle fibers, irritation of any of its sections, functional and morphological rearrangements (Fig. 8-17).
The appearance of multiple potentials of fasciculations in the muscles is considered one of the main signs of damage to the motor neurons of the spinal cord.
The exception is "benign" fasciculation potentials, sometimes detected in patients who complain of constant twitching in the muscles, but do not notice muscle weakness and other symptoms. Single fasciculation potentials can also be detected in neurogenic and even primary muscle diseases, such as myotonia, polymyositis, endocrine, metabolic and mitochondrial myopathies.
Rice. 8-17. Fasciculation potential against the background of complete relaxation of the deltoid muscle in a patient with bulbar form of ALS. The amplitude of the fasciculation potential is 1,580 μV. Resolution 200 µV/d, sweep 10 ms/d.
The potentials of fasciculations that occur in highly qualified athletes after exhausting physical activity are described. They can also occur in healthy, but easily excitable people, in patients with tunnel syndromes, polyneuropathy, and in the elderly. However, unlike diseases of motor neurons, their number in the muscle is very small, and the parameters are usually normal.
The parameters of fasciculation potentials (amplitude and duration) correspond to the parameters of the PMU recorded in a given muscle, and can change in parallel with changes in the PMU during the development of the disease.
Needle electromyography in the diagnosis of diseases of the motor neurons of the spinal cord and peripheral nerves
In any neurogenic pathology, DRP occurs, the severity of which depends on the degree of damage to the sources of innervation and on what level of the peripheral neuromotor apparatus - neuronal or axonal - the damage occurred. In both cases, the lost function is restored due to the remaining nerve fibers, and the latter begin to branch intensively, forming numerous sprouts heading towards the denervated muscle fibers. This branching has received the name "sprouting" in the literature (eng. "sprout" - sprout, branch).
There are two main types of sprouting - collateral and terminal.
Collateral sprouting - branching of axons in the area of Ranvier intercepts, terminal - branching of the terminal, unmyelinated section of the axon.
It is shown that the nature of sprouting depends on the nature of the factor that caused the violation of nervous control. For example, in botulinum intoxication, branching occurs exclusively in the zone of terminals, while in surgical denervation, both terminal and collateral sprouting take place.
On the EMG, these states are DE on various stages reinnervation process are characterized by the appearance of PDEs of increased amplitude and duration.
An exception is the very initial stages of the bulbar form of ALS, in which the PDE parameters are within the limits of normal variations for several months.
EMG criteria for diseases of the motor neurons of the spinal cord
The presence of pronounced fasciculation potentials (the main criterion for damage to the motor neurons of the spinal cord).
An increase in PDE parameters and their polyphasia, reflecting the severity of the reinnervation process.
The appearance in the muscles of spontaneous activity of muscle fibers - PF and surfactants, indicating the presence of a current denervation process.
Fasciculation potentials are an obligatory electrophysiological sign of damage to the motor neurons of the spinal cord. They are found already in the earliest stages of the pathological process, even before the appearance of signs of denervation.
Due to the fact that neuronal diseases imply a constant ongoing process of denervation and reinnervation, when a large number of motor neurons die simultaneously and the corresponding number of MUs is destroyed, PMUs become more and more enlarged, their duration and amplitude increase. The degree of increase depends on the duration and stage of the disease.
The severity of PF and POV depends on the severity of the pathological process and the degree of denervation of the muscle. In rapidly progressive diseases (for example, ALS), PF and POV are found in most muscles, in slowly progressive diseases (some forms of spinal amyotrophy) - only in half of the muscles, and in post-polio syndrome - in less than a third. EMG criteria for diseases of axons of peripheral nerves
Needle EMG in the diagnosis of peripheral nerve diseases is an additional, but necessary examination method that determines the degree of damage to the muscle innervated by the affected nerve. The study allows you to clarify the presence of signs of denervation (DF), the degree of loss of muscle fibers in the muscle (total number of SOVs and the presence of giant surfactants), the severity of reinnervation and its effectiveness (the degree of increase in PDE parameters, the maximum value of PDE amplitude in the muscle). The main emg signs of the axonal process:
- an increase in the average value of the PDE amplitude;
- the presence of PF and POV (with current denervation);
- an increase in the duration of PDE (the average value may be within the normal range, that is, ± 12%);
- polyphasia PDE;
- single potentials of fasciculations (not in every muscle).
With damage to the axons of peripheral nerves (various polyneuropathies), DRP also occurs, but its severity is much less than with neuronal diseases. Consequently, PDEs are enlarged to a much lesser extent. Nevertheless, the main rule for changing the PDE in neurogenic diseases also applies to damage to the axons of the motor nerves (that is, the degree of increase in the parameters of the PDE and their polyphasia depend on the degree of nerve damage and the severity of reinnervation). The exception is pathological conditions accompanied by rapid death of axons of motor nerves due to injury (or some other pathological condition leading to the death of a large number of axons). In this case, the same giant PDEs (with an amplitude of more than 5000 μV) appear as in neuronal diseases. Such PDEs are observed in long-term forms of axonal pathology, CIDP, and neural amyotrophies.
If with axonal polyneuropathy, the amplitude of the PDE first of all increases, then during the demyelinating process, with a deterioration in the functional state of the muscle (a decrease in its strength), the average duration of the PDE gradually increases; much more often than in the axonal process, polyphasic PDE and fasciculation potentials are found, and less often - PF and SOV.
Needle electromyography in the diagnosis of synaptic and primary muscle diseases
For synaptic and primary muscle diseases, a decrease in the average duration of PDE is typical. The degree of reduction in the duration of PDE correlates with a decrease in strength. In some cases, PDE parameters are within the limits of normal deviations, and with PMD they can even be increased (see Fig. 8-13).
Needle electromyography in synaptic diseases
In synaptic diseases, needle EMG is considered an additional research method. With myasthenia gravis, it allows you to assess the degree of "blockage" of muscle fibers in the MU, determined by the degree of reduction in the average duration of the PDE in the examined muscles. Nevertheless, the main goal of needle EMG in myasthenia gravis is to exclude possible comorbidities (polymyositis, myopathy, endocrine disorders, various polyneuropathies, etc.). Needle EMG in patients with myasthenia gravis is also used to determine the degree of response to the introduction of anticholinesterase drugs, that is, to assess the change in PDE parameters with the introduction of neostigmine methyl sulfate (prozerin). After the administration of the drug, the duration of PDE in most cases increases. Lack of response may indicate the so-called myasthenic myopathy.
The main EMG criteria for synaptic diseases:
- decrease in the average duration of PDE;
- a decrease in the amplitude of individual PDEs (may be absent);
- moderate PDE polyphasia (may be absent);
- the absence of spontaneous activity or the presence of only single PF.
With myasthenia gravis, the average duration of the PDE, as a rule, is slightly reduced (by 10-35%). The predominant number of PDEs has a normal amplitude, but several PDEs of reduced amplitude and duration are recorded in each muscle. The number of polyphasic PDEs does not exceed 15-20%. There is no spontaneous activity. If pronounced PF is detected in a patient, one should think about the combination of myasthenia gravis with hypothyroidism, polymyositis, or other diseases.
Needle Electromyography in Primary Muscular Diseases
Needle EMG is the main electrophysiological method for diagnosing primary muscle diseases (various myopathies). Due to the decrease in the ability of MUs to develop sufficient strength to maintain even a minimal effort, a patient with any primary muscle pathology has to recruit a large number of MUs. This determines the peculiarity of EMG in such patients. With minimal voluntary muscle tension, it is difficult to isolate individual PDEs, so many small potentials appear on the screen that it makes it impossible to identify them. This is the so-called myopathic EMG pattern (Fig. 8-18).
In inflammatory myopathies (polymyositis), a process of reinnervation takes place, which can cause an increase in PDE parameters.
Rice. 8-18. Myopathic pattern: measuring the duration of individual MUs is extremely difficult due to the recruitment of a large number of small MUs. Resolution 200 µV/d, sweep 10 ms/d.
The main EMG criteria for primary muscle diseases:
- decrease in the average duration of PDE by more than 1 2%;
- a decrease in the amplitude of individual PDEs (the average amplitude can be either reduced or normal, and sometimes increased);
- polyphasia PDE;
- pronounced spontaneous activity of muscle fibers in inflammatory myopathy (polymyositis) or PMD (in other cases it is minimal or absent).
A decrease in the average duration of PDE is a cardinal sign of any primary muscle disease. The reason for this change is that in myopathies, muscle fibers undergo atrophy, some of them fall out of the MU due to necrosis, which leads to a decrease in the PMU parameters.
A decrease in the duration of most PDEs is detected in almost all muscles of patients with myopathies, although it is more pronounced in the clinically most affected proximal muscles.
The histogram of PDE distribution by duration shifts towards smaller values (stages 1 or 11). PMD is an exception: due to the sharp PDE polyphasia, sometimes reaching 100%, the average duration can be significantly increased.
Electromyography of a single muscle fiber
EMG of a single muscle fiber makes it possible to study the electrical activity of individual muscle fibers, including determining their density in muscle MUs and the reliability of neuromuscular transmission using the jitter method.
A special electrode with a very small discharge surface 25 µm in diameter, located on its side surface 3 mm from the end, is required for the study. A small diverting surface allows recording the potentials of a single muscle fiber in a zone with a radius of 300 µm.
The study of the density of muscle fibers
The determination of muscle fiber density in DE is based on the fact that the microelectrode retraction zone for recording the activity of a single muscle fiber is strictly defined. A measure of the density of muscle fibers in MU is the average number of potentials of single muscle fibers recorded in the zone of its abduction in the study of 20 different MUs in different zones of the muscle. Normally, this zone can contain only one (rarely two) muscle fibers belonging to the same MU. With the help of a special methodical method(trigger device) it is possible to avoid the appearance on the screen of the potentials of single muscle fibers belonging to other MUs.
The average fiber density is measured in arbitrary units by counting the average number of potentials of single muscle fibers belonging to different MUs. In healthy people, this value varies depending on the muscle and age from 1.2 to 1.8. An increase in the density of muscle fibers in the MU reflects a change in the structure of the MU in the muscle.
Study of the Jitter Phenomenon
Normally, it is always possible to position the electrode for recording a single muscle fiber in a muscle so that the potentials of two adjacent muscle fibers belonging to one MU are recorded. If the potential of the first fiber will trigger the trigger device, then the potential of the second fiber will be slightly different in time, since it takes different times for the impulse to travel through two nerve terminals of different lengths. This is reflected in the variability of the peak-to-peak interval, that is, the registration time of the second potential fluctuates with respect to the first, defined as the "dance" of the potential, or "jitter", the value of which is normally 5-50 μs. Jitter reflects the variability in neuromuscular transmission time across the two motor end plates, so this method provides a measure of neuromuscular transmission stability. When it is violated, caused by any pathology, the jitter increases. Its most pronounced increase is observed in synaptic diseases, primarily in myasthenia gravis (Fig. 8-19).
With a significant deterioration in neuromuscular transmission, a state occurs when the nerve impulse cannot excite one of the two adjacent fibers and the so-called blocking of the impulse occurs (Fig. 8-20).
A significant increase in jitter and instability of individual PDE components are also observed in ALS. This is due to the fact that newly formed as a result of sprouting terminals and immature synapses work with an insufficient degree of reliability. At the same time, patients with rapid progression of the process have the most pronounced jitter and blocking of impulses.
Rice. 8-19. An increase in jitter (490 μs at a rate of less than 50 μs) in the common extensor of the fingers in a patient with myasthenia gravis (generalized form).
Superposition of 10 consecutively repeating complexes of two potentials of one DU. The first potential is the trigger one. Resolution 0.2 m V/d, sweep 1 ms/d.
Rice. 8-20. An increase in jitter (260 µs) and blocking of the impulse (on the 2nd, 4th and 9th lines) in the common extensor of the fingers of the same patient (see Fig. 8-19). The first impulse is the trigger.
Macroelectromyography
Macro-EMG makes it possible to judge the size of the DU in skeletal muscles. In the study, two needle electrodes are used simultaneously: a special macroelectrode inserted deep into the muscle so that the discharge side surface electrode, was located in the thickness of the muscle, and the usual concentric electrode inserted under the skin. The macro-EMG method is based on the study of the potential recorded by a macroelectrode with a large discharge surface.
A conventional concentric electrode serves as a reference electrode, inserted under the skin at a distance of at least 30 cm from the main macroelectrode into the zone of minimal activity of the muscle under study, that is, as far as possible from the motor point of the muscle.
Another electrode mounted in the cannula for recording the potentials of single muscle fibers registers the potential of the muscle fiber of the studied MU, which serves as a trigger for averaging the macropotential. The signal from the cannula of the main electrode also enters the averager. 130-200 pulses are averaged (an epoch of 80 ms, a period of 60 ms is used for analysis) until a stable isoline and stable amplitude DE macropotential appear. Registration is carried out on two channels: on one, a signal is recorded from one muscle fiber of the studied DU, which triggers averaging, on the other, a signal is reproduced between the main and reference electrode.
The main parameter used to assess the MU macropotential is its amplitude, measured from peak to peak. The duration of the potential when using this method does not matter. It is possible to estimate the area of macropotentials DE. Normally, there is a wide variation in the values of its amplitude, with age it slightly increases. In neurogenic diseases, the amplitude of DE macropotentials increases depending on the degree of reinnervation in the muscle. It is highest in neuronal diseases.
In the later stages of the disease, the amplitude of MU macropotentials decreases, especially with a significant decrease in muscle strength, which coincides with a decrease in PDE parameters recorded with standard needle EMG.
In myopathies, a decrease in the amplitude of DE macropotentials is noted, however, in some patients, their average values are normal, but nevertheless, a certain number of potentials of reduced amplitude are noted. None of the studies that studied the muscles of patients with myopathy revealed an increase in the average amplitude of MU macropotentials.
The macro-EMG method is very time-consuming, so it is not widely used in routine practice.
Scanning electromyography
The method makes it possible to study the temporal and spatial distribution of the DU electrical activity by scanning, that is, by stepwise movement of the electrode in the area where the fibers of the studied DU are located. Scanning EMG provides information on the spatial arrangement of muscle fibers throughout the MU space and may indirectly indicate the presence of muscle groups that are formed as a result of the process of denervation of muscle fibers and their re-innervation.
With a minimum voluntary muscle tension, the electrode inserted into it for recording a single muscle fiber is used as a trigger, and with the help of a concentric needle (scanning) electrode, the PDE is recorded from all sides with a diameter of 50 mm. The method is based on a slow step-by-step immersion of a standard needle electrode into the muscle, accumulation of information about changes in the parameters of the potential of a certain DU and the construction of an appropriate image on the monitor screen. Scanning EMG is a series of oscillograms located one below the other, each of which reflects fluctuations in the biopotential registered at a given point and captured by the discharge surface of a concentric needle electrode.
The subsequent computer analysis of all these PDEs and the analysis of their three-dimensional distribution gives an idea of the electrophysiological profile of motor neurons.
When analyzing the data of scanning EMG, the number of main PDE peaks, their shift in time of appearance, the duration of the intervals between the appearance of individual fractions of the potential of a given DU, and the diameter of the fiber distribution zone in each of the examined DUs are calculated.
With DRP, the amplitude and duration, as well as the area of potential oscillations on the scanning EMG, increase. However, the diameter of the fiber distribution zone of individual DUs does not change significantly. The number of fractions characteristic of a given muscle also does not change.
Normally, in a relaxed muscle, no spontaneous activity is recorded. In neurogenic diseases, two types of spontaneous activity of muscle fibers can be recorded - fibrillation potentials (PF) and positive sharp waves (POS). PF in neurogenic (and synaptic) diseases are the potentials of denervated muscle fibers that have lost their connection with axon terminals, but they can be reinnervated and become part of another motor unit. POV is an EMG sign of dead muscle fibers, which for some reason could not receive innervation. The more IF registered in a muscle, the greater the degree of its denervation. The more POV detected in a muscle, the more dead muscle fibers it contains.
Regarding the detection of spontaneous activity of muscle fibers in patients with myasthenia gravis, there is also no consensus in the literature. Some authors mentioned the presence of PF and POV in patients with myasthenia, others did not find them. In our study, PF and SOV were detected in 33% of the examined muscles of patients with myasthenia gravis, but their number in the muscle was not large and ranged from 1 to 5 PF (mean number 1.3+1.1). In 67% of the muscles of patients in this group, spontaneous activity was not detected. It was also noted that PF are detected much more often in patients with myasthenia gravis in combination with thymoma.
SOVs were detected only in 21% of the muscles, and they were recorded in the same muscles in which PF were also detected. Their severity in the muscle did not exceed 2 SOV, the average value was only 0.4±0.7 SOV. Single fasciculation potentials (PFCs) were detected in 13% of the muscles.
The obtained results showed that in patients with myasthenia, in some cases, there is denervation of individual muscle fibers, which manifests itself in the form of PF, while POV, indicating the death of a muscle fiber, was detected in rare cases and were isolated.
These data allow us to believe that the appearance of spontaneous activity of muscle fibers in patients with myasthenia gravis is explained by the presence of far-reaching denervation changes caused by a neuromuscular transmission disorder characteristic of myasthenia gravis. This is consistent with the fact of the absence of spontaneous activity in the vast majority of patients with reversible disorders of neuromuscular transmission, as well as with an increase in the degree of its severity in the muscles, in which, after the administration of prozerin, it was not possible to achieve a complete restoration of the duration of PDE. At the same time, only in 11% of such muscles PF were detected, and only in 3% - SOV. In those cases where the administration of prozerin resulted in only partial compensation of the synaptic defect, PF and SOV were recorded in a larger number of muscles.
Myasthenic syndromes
MYASTENIC SYNDROME SOMETIMES ASSOCIATED WITH BRONCHOGENIC CARCINOMA (LAMBERT-EATHON SYNDROME)
A detailed clinical and electrophysiological study of myasthenic syndrome, sometimes combined with small cell lung carcinoma, was carried out in 1956 by Lambert E. and Eaton L., in connection with which he received the name "Lambert-Eaton myasthenic syndrome" (MSLI).
Their results were based on a study of 6 patients, 5 of whom were men: 2 patients had small cell carcinoma, 1 had lung reticulosarcoma; one patient had cerebellar ataxia without signs of carcinomatous lesions. All patients had muscle weakness and fatigue, electrophysiological features, and a response to anticholinesterase drugs other than myasthenia gravis.
The ratio of men and women, according to most researchers, is 1.5:1. The age of patients with MSLI varies in wide range(14-80 years old).
According to the literature, small cell carcinoma is detected in 90% of cases, although there are cases of combination with other types of lung tumors, with a kidney tumor, acute leukemia, reticulosarcoma, and even one observation concerns the combination of MCLI with malignant thymoma.
The time from the appearance of the first clinical signs of MSLI to the discovery of a tumor is approximately 3 years.
It is important to emphasize the fact that clinical manifestations myasthenic syndrome and electrophysiological characteristics of neuromuscular transmission disorders in patients with MSLI with and without bronchogenic carcinoma do not differ. According to most researchers, they do not differ in the features of the immune response, in particular, the titer of antibodies to voltage-gated calcium channels (PCCs).
According to modern concepts, MSLI, both with and without bronchogenic carcinoma, is an autoimmune disease, the pathogenesis of which is associated with the presence of autoantibodies to voltage-gated calcium channels (PCCs) of the presynaptic membrane of the neuromuscular junction.
An experimental study of the morphofunctional organization of the axon terminal membrane made it possible to distinguish four types of voltage-dependent calcium channels (P/Q, N, L, and T), which differ from each other in the rate of opening and the ability of various poisons to block these channels. In the blood serum of approximately 90% of patients with MCLI, antibodies to voltage-gated calcium channels of the P/Q type are detected. However, a number of researchers also found antibodies to N and L type channels.
In patients with MCLI, both with and without signs of a paraneoplastic process, in addition to specific autoantibodies, antibodies are also detected that are directed both against various antigenic targets of the neuromuscular junction and others, such as the gastric mucosa, thyroid tissue, Purkinje cells and other neuronal structures. Most researchers do not detect autoantibodies to acetylcholine receptors typical for myasthenia gravis in patients with MCLI.
The literature describes a group of patients with a combination of myasthenia gravis and MCLI - overlap myasthenic syndrome, in which clinical signs of either myasthenia gravis or MCLI may prevail at different periods of the course of the disease and, accordingly, antibodies to both AChR and PCC can be detected.
The symptoms of MSLI are:
Weakness and fatigue of the proximal legs and pelvic girdle, leading to a change in gait - "duck". Weakness of the proximal parts of the hands is expressed to a much lesser extent.
Oculomotor disturbances are detected very rarely and their severity is usually minimal. Swallowing and speech disorders are also rare.
Disturbances in the function of the autonomic nervous system with impaired salivation and sweating, up to the development of "dry syndrome", orthostatic hypotension, paresthesia, observed in approximately 65% of patients, impotence.
Absence or significant inhibition of deep reflexes.
The inconsistency of patients' complaints of weakness and the absence of a real decrease in muscle strength in the tested muscles. This circumstance is associated with the peculiarities of neuromuscular transmission disorders, which is manifested by an increase in muscle strength during physical activity and a change in the reflex excitability of the affected muscle groups.
In 90% of patients with MCLI, the effect of anticholinesterase drugs is questionable at best.
The use of drugs that facilitate the release of the mediator from the axon terminal, such as guanidine, 3-4-diaminopyridines, 4-aminopyridines, neuromidine (ipidacrine), as well as intravenous calcium, has a significantly greater effect than taking anticholinesterase drugs
One of the most important criteria for the diagnosis and differential diagnosis of SMLI is an electromyographic study of the state of neuromuscular transmission by indirect supramaximal muscle stimulation.
The study of groups of patients with MSLI, different in sex and age, the presence or absence of bronchogenic carcinoma, showed that the main characteristics of the neuromuscular transmission block are:
Low amplitude M-response (negative phase less than 5.0 mV);
Increase - the increment of the amplitude of subsequent M-responses in a series with high-frequency stimulation (20-50 imp/s) more than 200%;
M-response amplitude increment in response to the second of a pair of stimuli with an interpulse interval (MI) from 50 to 20 ms;
Significant - more than 200% - the value of post-tetanic relief.
Congenital myasthenic syndromes (KMC) is a group of hereditary neuromuscular diseases caused by a mutation of the genes responsible for the formation and functional state acetylcholine receptors, ion channels and enzymes that ensure the reliability of the conduction of excitation from the nerve to the muscle.
Of 276 patients with KMC seen at the Mayo Clinic between 1988 and 2007, a presynaptic defect was found in 20 patients, a synaptic defect in 37, and a postsynaptic defect in 219.
KMS classification:
Presynaptic defects (7%):
Myasthenic syndrome with choline acetyltransferase deficiency;
Myasthenic syndrome with a decrease in synaptic vesicles and quantum release of the mediator;
Lambert-Eaton-like syndrome.
- nunidentified defects
Synaptic defects (13%):
Myasthenic syndrome with acetylcholinesterase deficiency.
Postsynaptic defects (80%):
Primary kinetic pathology with or without deficiency of ACh receptors:
Slow channel syndrome;
Fast channel syndrome.
Primary deficiency of ACh receptors with a slight kinetic defect:
Myasthenic syndrome with rapsin deficiency;
Dok 7-myasthenia gravis;
Myasthenic syndrome associated with the pathology of Na-channels;
Myasthenic syndrome with plectin deficiency.
Genetic analysis of the acetylcholine receptor (AChR) subunits in patients with KMC has revealed numerous mutations associated with these diseases. Most KMC are postsynaptic, and their molecular genetic defect is based on mutations in the genes of various subunits of acetylcholine receptors (a, b, d, e). In some cases, this is manifested by kinetic anomalies of the receptors themselves, leading to disruption of their interaction with the mediator; in others, they are due to the predominant AChR deficiency associated with their death.
Primary sequencing and mutation analysis of the collagen chain of the human endplate acetylcholinesterase subunit has revealed the molecular basis of the acetylcholinesterase deficiency syndrome. In addition, electrophysiological study using microelectrode technique (patch clamping) of the end plate of human muscles allows you to determine the individual channel currents passing through normal or mutated AChR channels.
Accurate diagnosis of various types of KMC is very important for rational therapy.
As a rule, the diagnosis of KMC is based on clinical evidence of a history of fatigue weakness in the ocular, bulbar and trunk muscles, manifested since infancy or early childhood, a family history (similarly affected relatives), a decrement of M-response parameters on EMG examination, and a negative antibody test to acetylcholine receptors. However, in some forms of KMC, however, there is a later onset of the disease. Slow-channel syndrome - onset at any age, familial limb-girdle Dok 7-myasthenia gravis - typical onset at 5 years old, possibly beginning at 13 to 19 years. In childhood myasthenia gravis associated with choline acetyltransferase deficiency, all symptoms may be episodic with severe respiratory crises on the background of fever, excitement or no apparent reason and the complete absence of symptoms in the interictal period. The absence of a family history does not rule out an autosomal recessive pattern of inheritance, a defective perinatal autosomal dominant gene in one of the parents, or a new mutation. Neuromuscular transmission disorders do not occur in all muscles or consistently, and the distribution of muscle weakness is limited.
There are certain clinical signs that allow differentiating different syndromes.
Thus, in patients with severe involvement of the trunk (truncal) or axial muscles, as in AChE deficiency, dysraphic features quickly develop with the formation of postural scoliosis and a change in one foot relative to the other in a vertical position. Selective weakness of the muscles of the neck, forearm, and finger extensors is typical of Slow-channel syndrome and in elderly patients with cholinesterase deficiency. Decreased pupillary response to light is observed in cholinesterase deficiency. Involvement of the ocular muscles may be absent or mild in cholinesterase deficiency, Slow-channel syndrome, Dok 7 familial myasthenia gravis. Tendon reflexes are usually elicited but are reduced in about one in five patients with cholinesterase deficiency and in severe weakness in patients with a mutation that affects the e-subunit of the AChR.
Significant assistance in the diagnosis of KMC is also provided by a pharmacological test with the introduction of anticholinesterase drugs. For example, patients with AChE enzyme deficiency and Slow-channel syndrome do not respond to AChE inhibitors, and the administration of drugs causes a deterioration in the condition of patients.
The diagnosis of KMC is usually confirmed by the presence of a decrement during low-frequency indirect muscle stimulation (2-3 Hz) in one of the most affected muscles or an increase in jitter and blocking when examining the potentials of individual muscle fibers (single-fiber). Decrement may be absent in myasthenic syndrome with choline acetyltransferase deficiency and between attacks in myasthenic syndrome with a decrease in synaptic vesicles and quantum release of the mediator. In this syndrome, decrement can be induced by prolonged rhythmic stimulation at a frequency of 10 Hz or exercise within a few minutes before the testing series - stimulation with a frequency of 2 Hz.
In patients with AChE deficiency and Slow-channel syndrome, a single supramaximal stimulus elicits a repeated M-response (CMAP). The interval between the first and subsequent potentials is 5-10 ms. The decrement during stimulation with a frequency of 2-3 Hz is accompanied by a decrease in the second component more rapidly than the main one. The test should be performed in patients not receiving AChE inhibitors after a period of rest (rest) and with single nerve stimulation.
The amplitude of the first component of the M-response is usually normal, but the low-amplitude second component increases during physical exertion or after injection of anticholinesterase drugs.
A positive test for antibodies to the acetylcholine receptor and to muscle specific tyrosine kinase (MuSK) rules out congenital myasthenic syndrome. At the same time, a negative test cannot unequivocally confirm KMC, given the presence of seronegative forms of myasthenia gravis. However, strong evidence for the absence of seronegative myasthenia gravis is the absence of immune deposits (IgG and complement) on the end plate.
Morphohistochemical study of muscle biopsy specimens with KMC does not reveal any pathology that makes it possible to differentiate these conditions from the results of a study of patients with autoimmune myasthenia gravis. As a rule, atrophies of muscle fibers of the 2nd type are detected. In some cases, the predominance of the number of muscle type 1. These findings, however, are not specific, but may somehow answer the question of the presence of KMC.
In some cases, it is possible with a sufficient degree of probability to assume the presence of a certain clinical form of KMC, but the assumption may be erroneous. Thus, a repeated M-response to a single supramaximal stimulus is observed only in two KMCs - congenital cholinesterase deficiency and Slow-channel syndrome. At the same time, similar changes in the parameters of the M-response were also observed in patients with autoimmune myasthenia gravis with the development or threat of development of a mixed crisis.
Refractoriness to taking anticholinesterase drugs and delayed pupillary response to light indicate a congenital endplate cholinesterase deficiency, but similar symptoms are observed in patients with autoimmune myasthenia gravis during the development of a crisis.
Selective weakness of the muscles of the neck, wrist, and extensor muscles of the fingers is seen in Slow-channel syndrome and in older patients with endplate cholinesterase deficiency. A similar type of distribution of movement disorders is observed in patients with late onset myasthenia gravis and myasthenia gravis, combined with thymoma, who have an undoubted autoimmune pathology.
In KMC, resembling Lambert-Eaton syndrome, the first evoked M-response has a low amplitude, but facilitation of more than 100% to high stimulation frequencies is noted, which makes it impossible to distinguish it from an autoimmune syndrome associated with the presence of autoantibodies to voltage-gated calcium channels of the P / Q type. .
KMC accompanied by episodes of apnea, with a history of repeated episodes of apnea, occurring both spontaneously and against the background of fever, vomiting, excitement or agitation. In this case, between attacks of apnea, patients can either be completely healthy or have moderate myasthenic manifestations. There may or may not be ptosis of the eyelids, and, as a rule, there are restrictions on the mobility of the eyeballs. The amplitude decrement of the M-response may not be detected in a rested muscle, but it appears after several minutes of stimulation at a frequency of 10 pulses/s. These manifestations are characteristic of myasthenic syndrome with a decrease in synaptic vesicles and quantum release of the neurotransmitter.
KMC associated with plectin deficiency and observed in patients with hereditary bullous dermatitis and a form of muscular dystrophy. Deficiency of plectin (immunoreactivity) - a normal component that is present in the hemidermosomes of the skin, in the sarcolemma, in the postsynaptic membrane and in the nuclear membrane of muscles - reduces the virulence of skin microorganisms (thinns or softens) and plectin is absent from the muscle.
In these and other KMC, the phenotype is not informative, and to determine the level of suffering (pre- or postsynaptic nature), a specialized electrophysiological and molecular genetic study is needed to determine the etiology and / or mutation underlying the disease.
