Needle electromyography

Needle electromyography includes the following main techniques:

• standard needle EMG;
• EMG of a single muscle fiber;
• macroEMG;
• scanning EMG.

Standard Needle Electromyography

Needle electromyography is an invasive method of investigation, carried out with the help of a concentric needle electrode introduced into the muscle. Needle electromyography allows evaluating the peripheral neuromotor apparatus: the morphofunctional organization of skeletal muscle DE, 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.

Diagnostic value

Standard needle electromyography takes a central place among electrophysiological research methods for various neuromuscular diseases and is crucial in the differential diagnosis of neurogenic and primary-muscular diseases.

With the help of this method, the severity of denervation in the muscle innervated by the affected nerve is determined, the degree of its restoration, and the effectiveness of the reinnervation.

Needle electromyography 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.

[1], [2], [3], [4], [5]

Indications for the procedure

Diseases of spinal cord motoneurons ( ALS, spinal amyotrophies, poliomyelitis and post- poliomyelitis syndrome, syringomyelia, etc.), myelopathies, radiculopathies, various neuropathies (axonal and demyelinating), myopathies, muscle inflammation ( polymyositis and dermatomyositis ), central motor disorders, sphincter disorders and a number of other situations, when it is necessary to objectify the state of the motor functions and the motion control system, to evaluate the involvement of various structures in the process peripherally neuromotor apparatus.

[6]

Preparation

Special preparation of the patient for the study is not necessary. Needle electromyography requires complete relaxation of the examined muscles, so it is carried out in the patient's lying position. The patient is exposed to the muscles to be examined, placed on his back (or abdomen) on a comfortable soft couch with an adjustable head, inform him of the upcoming examination and explain how he should strain and then relax the muscle.

[7]

Technique of the needle electromyography

The examination is carried out with the help of a concentric needle electrode inserted into the locomotive point of the muscle (the permissible radius is no more than 1 cm for large muscles and 0.5 cm for small muscles). The potentials of DE (PDE) are recorded. When choosing a PDE for analysis, it is necessary to follow certain rules for their selection.

Reusable needle electrodes are previously sterilized in an autoclave or other sterilization methods. Disposable sterile needle electrodes are opened immediately before the examination of the muscle.

After the introduction of the electrode into the completely relaxed muscle and every time it is moved, the possible appearance of spontaneous activity is monitored. Registration of PDE is performed with minimal arbitrary muscle tension, which allows identifying individual PDEs. 20 different PDEs are selected, observing a certain sequence of electrode displacement in the muscle.

When assessing the condition of the muscle, a quantitative analysis of the detected spontaneous activity is carried out, which is especially important in monitoring the patient's condition in dynamics, as well as in determining the effectiveness of therapy. Analyze the parameters of the registered potentials of different DE.

Needle electromyography in synaptic diseases

With synaptic diseases, needle electromyography is considered an additional method of investigation. In myasthenia, it allows to assess the degree of "blocking" of muscle fibers in DE, determined by the degree of decrease in the mean duration of PDE in the muscles examined. Nevertheless, the main goal of needle electromyography in myasthenia is the elimination of possible concomitant pathologies (polymyositis, myopathy, endocrine disorders, various polyneuropathies, etc.). Needle electromyography in patients with myasthenia is also used to determine the degree of response to the administration of anticholinesterase drugs, that is, to evaluate the change in the parameters of PDE with the introduction of neostigmine methyl sulphate (proserin). After the administration of the drug, the duration of PDE increases in most cases. The lack of response can serve as an indication of the so-called myasthenic myopathy.

The main electromyographic criteria for synaptic diseases:

• decrease in the average duration of the PDE;
• a decrease in the amplitude of individual PDEs (may be absent);
• moderate polyphasia of PDE (may be absent);
• The absence of spontaneous activity or the presence of only a single PF.

In myasthenia gravis, the average duration of PDE, as a rule, is reduced insignificantly (by 10-35%). The predominant amount of PDE has a normal amplitude, but several PDEs of reduced amplitude and duration are recorded in each muscle. The number of polyphase PDEs does not exceed 15-20%. Spontaneous activity is absent. When identifying the patient expressed PF, one should think about the combination of myasthenia with hypothyroidism, polymyositis or other diseases.

Needle electromyography in primary muscular diseases

Needle electromyography is the main electrophysiological method for diagnosis of primary muscular diseases (various myopathies). Due to the decrease in the ability of the DE to develop sufficient strength to maintain even minimal effort, a patient with any primary muscular pathology has to recruit a large number of DE. This determines the feature of electromyography in such patients. With minimal voluntary muscle tension, it is difficult to single out individual PDEs, so many small potentials appear on the screen, which makes it impossible to identify them. This is the so-called myopathic pattern of electromyography.

With inflammatory myopathies (polymyositis), the reinnervation process takes place, which can cause an increase in the parameters of the PDE.

Basic electromyographic criteria of primary muscular diseases:

• decrease in the average duration of the PDE by more than 12%;
• decrease in the amplitude of individual PDEs (the average amplitude can be either reduced, or normal, and sometimes increased);
• polyphase of PDE;
• marked spontaneous activity of muscle fibers in inflammatory myopathy (polymyositis) or PMD (in other cases it is minimal or absent).

Reducing the average duration of PDE is a cardinal sign of any primary-muscle disease. The reason for this change is that in myopathies, the muscle fibers undergo atrophy, some of them drop out of the DE composition because of necrosis, which leads to a reduction in the parameters of the PDE. Reduction of 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 the PDE distribution in terms of duration shifts towards smaller values (stage I or II). The exceptions are PMD: due to the sharp polyphase PDE, sometimes reaching 100%, the average duration can be significantly increased.

Electromyography of a single muscle fiber

Electromyography of a single muscle fiber allows you to study the electrical activity of individual muscle fibers, including determining their density in the DE muscle and the reliability of neuromuscular transmission using the jitter method.

A special electrode with a very small discharge surface of 25 μm in diameter, located on its lateral surface 3 mm from the end, is required for the study. A small discharge surface allows one to register the potentials of a single muscle fiber in a 300-μm radius zone.

[8], [9]

Investigation of the density of muscle fibers

The basis for determining the density of muscle fibers in DE is the fact that the microelectrode extraction zone for recording the activity of a single muscle fiber is strictly defined. The measure of the density of muscle fibers in DE is the average number of potentials of single muscle fibers recorded in the zone of its retraction when examining 20 different DE in different muscle zones. Normally in this zone there can be only one (more rarely two) muscle fibers belonging to the same DE. With the help of a special methodical technique (trigger device), it is possible to avoid appearing on the screen potentials of single muscle fibers belonging to other DE.

The average density of the fibers is measured in conventional units, by calculating the average number of potentials of single muscle fibers belonging to different DE. In healthy people this value varies depending on the muscle and age from 1.2 to 1.8. The increase in the density of muscle fibers in DE reflects the change in the structure of DE in the muscle.

Investigation of the jitter phenomenon

Normally, it is always possible to arrange an electrode to record a single muscle fiber in the muscle so that the potentials of two adjacent muscle fibers belonging to the same DE are recorded. If the potential of the first fiber triggers the trigger device, the potential of the second fiber will not coincide in some time, since a different time is required for the pulse to travel through two different terminals of different lengths. This is reflected in the variability of the inter-peak interval, that is, the recording time of the second potential varies 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 of the neuromuscular transmission time in the two motor end plates, so this method allows one to study the measure of the stability of the neuromuscular transmission. With its violation, caused by any pathology, jitter increases. The most pronounced increase is observed with synaptic diseases, especially in myasthenia gravis.

With a significant deterioration of the neuromuscular transmission, a state occurs when the nerve impulse can not excite one of the two adjacent fibers and the so-called pulse blocking occurs.

A significant increase in jitter and instability of individual components of the PDE are observed with ALS. This is due to the fact that newly formed as a result of scaling, terminals and immature synapses work with an insufficient degree of reliability. In this case, the most pronounced jitter and blocking of impulses are noted in patients with rapid progression of the process.

Macroelectromyography

Macroelectromyography allows you to judge the size of DE in skeletal muscles. In the study, two needle electrodes are simultaneously used: a special macroelectrode injected deep into the muscle so that the outlying side surface of the electrode is in the muscle mass and a conventional concentric electrode inserted under the skin. The method of macroelectromyography is based on the study of the potential recorded by a macroelectrode with a large discharge surface.

A conventional concentric electrode serves as reference, placed under the skin at a distance of at least 30 cm from the main macroelectrode into the zone of minimal activity of the muscle being studied, that is, as far as possible from the motor point of the muscle.

The other electrode, which is mounted in the cannula for recording the potentials of single muscle fibers, registers the potential of the muscle fiber of the DE being studied, which serves as a trigger for averaging the macro potential. The averager also receives a signal from the cannula of the main electrode. Averaging 130-200 pulses (an epoch of 80 ms, a period of 60 msec used for the analysis) until a stable isoline and a stable macro-potential DE appear in the amplitude. The registration is carried out on two channels: one records the signal from one muscle fiber of the DE that starts the averaging, while the other reproduces the signal between the reference electrode and the reference electrode.

The main parameter used to estimate the macro-potential DE 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 macro potentials of DE. Normally, there is a wide variation in the magnitude of its amplitude, it increases somewhat with age. With neurogenic diseases, the amplitude of DE macro-potentials rises depending on the degree of reinnervation in the muscle. With neuronal diseases, it is the highest.

In the late stages of the disease, the amplitude of the DE macro-potentials decreases, especially with a significant decrease in muscle strength, which coincides with a decrease in the parameters of the PDE registered with standard needle electromyography.

In myopathies, a decrease in the amplitude of the macrotopotentials of DE is noted, but in some patients their average values are normal, but nevertheless, nevertheless, they note a certain number of potentials of a reduced amplitude. None of the studies that studied the muscles of patients with myopathy showed an increase in the average amplitude of DE macro-potentials.

The method of macroelectromyography is very time consuming, so in the routine practice of widespread use, he did not receive it.

Scanning electromyography

The method makes it possible to study the temporal and spatial distribution of the electric activity of DE by scanning, that is, stepwise displacement of the electrode in the fiber region of the investigated DE. Scanning electromyography provides information on the spatial arrangement of muscle fibers throughout the DE space and can indirectly indicate the presence of muscle groups that are formed as a result of the process of denervation of muscle fibers and their re-reinvention.

With minimal arbitrary muscle tension, an electrode introduced into it to record a single muscle fiber is used as a trigger, and a PDE is registered with a 50-mm-diameter PDE on all sides using a retracting concentric needle (scanning) electrode. The method is based on a slow step-by-step immersion in the muscle of a standard needle electrode, accumulation of information about the change in the parameters of the potential of a certain DE, and the construction of an appropriate image on the monitor screen. Scanning electromyography is a series of oscillograms arranged one under the other, each reflecting the oscillations of the biopotential recorded at a given point and captured by the discharge surface of a concentric needle electrode.

Subsequent computer analysis of all these PDEs and analysis of their three-dimensional distribution gives an idea of the electrophysiological profile of motoneurons.

When analyzing the data of scanning electromyography, the number of main peaks of the PDE, their displacement by the time of appearance, the duration of intervals between the appearance of individual fractions of the potential of this DE, and the width of the fiber distribution zone in each of the examined DEs are estimated.

In ADP, the amplitude and duration, as well as the area of potential oscillations on scanning electromyography, increase. However, the width of the distribution zone of the fibers of individual AE does not change significantly. The number of fractions characteristic for a given muscle does not change either.

Contraindications to the procedure

There are practically no contraindications to conducting needle electromyography. The unconscious state of the patient is considered a limitation, when he can not arbitrarily strain the muscle. However, in this case it is also possible to determine the presence or absence of the current process in the muscles (by the presence or absence of spontaneous activity of the muscle fibers). With caution should be carried out needle electromyography in those muscles in which there are pronounced purulent wounds, non-healing ulcers and deep burn injuries.

[10], [11]

Normal performance

DE is a structural and functional element of the skeletal muscle. It is formed by the motor motoneuron located in the anterior horn of the gray substance of the spinal cord, its axon emerging as a myelinated nerve fiber in the motor spine, and a group of muscle fibers that form the synapses with the myelin sheath without the numerous branches of this axon - the terminals.

Each muscular muscle fiber has its own terminal, is part of only one DE and has its own synapse. Axons begin to branch intensively at a level of several centimeters to the muscle to provide innervation of each muscle fiber that is part of this DE. Motoneuron generates a nerve impulse that is transmitted along the axon, amplified in the synapse and causes a reduction in all muscle fibers belonging to this DE. The total bioelectric potential recorded with such a reduction in muscle fibers is called the potential of the motor unit.

The potentials of motor units

The judgment about the state of DE of human skeletal muscles is obtained on the basis of 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 the muscle fibers that make up the DE, which functions as a single whole.

When the excitation wave propagates through the muscle fibers towards the electrode, a three-phase potential appears on the monitor screen: the first deviation is positive, then a rapid negative peak occurs, and the potential ends with a third, again positive deviation. These phases can have different amplitude, duration and area, which depends on how the discharge surface of the electrode is located in relation to the central part of the recorded DE.

Parameters of the PDE reflect the dimensions of the DE, the amount, the relative position of the muscle fibers and the density of their distribution in each particular DE.

[12], [13]

Duration of potentials of motor units is normal

The main parameter of the PDE is its duration, or duration, measured as the time in milliseconds from the beginning of the deviation of the signal from the center line to a full return to it.

Duration of PDE in a healthy person depends on muscle and age. With age, the duration of the PDE increases. To create unified standard criteria for the study of PDE, special tables of normal mean values of duration for different muscles of people of different ages have been developed. A fragment of such tables is given below.

Measurement of the state of DE in the muscle is the average duration of 20 different PDEs recorded at different points in the muscle being studied. The mean value obtained in the study is compared with the corresponding index presented in the table, and the deviation from the norm (in percent) is calculated. The average duration of the PDE is considered normal if it fits within ± 12% of the value given in the table (abroad, the average duration of the PDE is considered normal if it falls within ± 20%).

[14], [15], [16], [17]

Duration of potentials of motor units in pathology

The main regularity of the change in the duration of PDE in pathological conditions is that it increases with neurogenic diseases and decreases with synaptic and primary-muscle pathology.

In order to more thoroughly assess the degree of change in the PDE in muscles with various lesions of the peripheral neiromotor apparatus, a histogram of the PDE distribution over the duration is used for each muscle, since their average value can 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 neiromotor apparatus, the shape of the histogram changes significantly.

[18], [19]

Electromyographic stages of the pathological process

Based on the change in the duration of the PDE in diseases of the spinal cord motoneurons, when all the changes occurring in the muscles can be traced in a relatively short time, six EMG stages reflecting the general patterns of DE restructuring during the denervation-reinnervation process (ADD), from the very onset of the disease to almost complete loss of muscle.

With all neurogenic diseases, more or less motoneurons or their axons die. Preserved motoneurons innervate the "alien" muscle fibers, deprived of nervous control, thereby increasing their number in their DE. In electromyography, this process is manifested by a gradual increase in the parameters of the potentials of such DE. The entire cycle of changing the histogram of the distribution of PDE by duration for neuronal diseases conditionally fits into five EMG stages reflecting the process of compensatory innervation in muscles. This division is conditional, although it helps to understand and follow all stages of the development of the EA in each specific muscle, since each stage reflects a certain phase of reinnervation and the degree of its expression. Stage VI to present in the form of a histogram is inexpedient, since it reflects the final point of the "reverse" process, that is, the process of decompensation and destruction of the DE muscle.

Among the specialists of our country, these stages have become widespread in the diagnosis of various neuromuscular diseases. They are included in the computer program of domestic electromyographs, which allows the automatic construction of histograms with the designation of the process stage. Changing the stage in one direction or the other during a second examination of the patient shows what further prospects for the development of an ACE are.

• I stage: the average duration of the 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 has not yet been electromiographically manifested. From the composition of some DE, some part of the denervated muscle fibers, lacking impulse influence due to pathology or motoneuron, or its axon, falls out. The number of muscle fibers in such DE decreases, which leads to a decrease in the duration of individual potentials. In the first stage, a certain number of narrower potentials appears than in a healthy muscle, which causes a slight decrease in the mean duration. The histogram of the PDE distribution begins to shift to the left, towards smaller values.
• II stage: the average duration of the PDE is reduced by 21% or more. In DRP, this stage is marked extremely rarely and only in those cases when, for some reason, the reinnervation does not occur or is suppressed by some factor (for example, alcohol, radiation, etc.), and denervation, on the contrary, increases and a massive death of muscle fibers in DE. This leads to the fact that most or practically all of the PDEs become less 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 DE, caused by a decrease in the number of functioning muscle fibers in them.
• III stage: mean duration of PDE is within ± 20% of the norm for a given muscle. This stage is characterized by the appearance of a certain number of potentials of increased duration, normally not detectable. The appearance of these PDEs indicates the beginning of the reinnervation, that is, the dener-muscular muscle fibers begin to be included in other DEs, in connection with which the parameters of their potentials increase. In the muscle at the same time registering PDE as reduced and normal, and increased duration, the number of enlarged PEU in the muscle varies from one to several. The average duration of PDE in stage III may be normal, but the histogram is different from normal. It does not have the form of a normal distribution, but is "flattened", stretched, and begins to shift to the right, toward larger values. It is proposed to divide stage III into two subgroups - IIIA and IIIB. They differ only in that, with stage IIIA, the average duration of the PDE is reduced by 1-20%, and at stage IIIB it either completely coincides with the average value of the norm, or increased by 1-20%. In the SB stage, a slightly larger amount of PDE is recorded with an increased duration than in stage IIIA. Practice has shown that this division of the third stage into two subgroups is of no special significance. In fact, the third stage simply means the appearance of the first EMG signs of reinnervation in the muscle.
• IV stage: mean duration of PDE increased by 21-40%. This stage is characterized by an increase in the average duration of the PDE due to the appearance, in addition to normal PDEs, of a large number of potentials of increased duration. The reduced duration in the present stage is rarely recorded. The histogram is shifted to the right, in the direction of larger values, its shape is different and depends on the ratio of the normal and extended duration of the PDE.
• V stage: the average duration of the PDE is increased by 41% or more. This stage is characterized by the presence of predominantly large and "giant" PDEs, and there are practically no PDEs of normal duration. The histogram is significantly shifted to the right, stretched and, as a rule, opened. This stage reflects the maximum volume of reinnervation in the muscle, as well as its effectiveness: the more gigantic PANEs, the more effective the 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 changes in the form of PEU (potentials of collapsing DE). 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, they are rounded, the potential increase time is sharply increased. This stage is noted at the last stage of decompensation of the pulmonary artery disease, when the majority of motoneurons of the spinal cord have already died and the intensive death of the others occurs. Decompensation of the process begins from the moment when the process of denervation is growing, and the sources of innervation become less and less. At the EMG, the decompensation stage is characterized by the following features: the parameters of the PDE begin to decrease, the giant PDEs gradually disappear, the intensity of the PF sharply increases, giant POWs appear, which indicates the death of many nearby lying muscle fibers. These signs indicate that in this muscle, motoneurons have exhausted their abilities for scaffolding as a result of functional inferiority and are no longer able to exercise full control over their fibers. As a consequence, the number of muscle fibers in the DE decreases progressively, the mechanisms of impulse conduction are violated, the potentials of such DE are rounded, their amplitude decreases, and the duration decreases. The construction of a histogram in this stage of the process is inexpedient, since it, as well as the average duration of the PDE, no longer reflects the true state of the muscle. The main feature of stage VI is the change in the form of all the PDVs.

EMG stages are used not only for neurogenic, but also for various primary muscular diseases, in order to characterize the depth of muscle pathology. In this case, the EMG stage does not reflect ADP, but the severity of the pathology and is called the "EMG stage of the pathological process." In primary muscular dystrophies, abruptly polyphasic PDE with satellites that increase their duration can appear, which significantly increases the average value corresponding to the III or even IV EMG of the pathological process stage.

[20], [21], [22]

Diagnostic significance of EMG stages

• In neuronal diseases, different EMG stages are often found in different muscles in the same muscle - from stage III to VI, the stage is very rarely detected - at the very beginning of the disease, and only in separate muscles.
• In axonal and demyelinating diseases, III and IV are more often detected, less often - stages I and II. With the death of a significant number of axons in the individual most affected muscles, the V stage is revealed.
• In primary muscular diseases, the muscle fibers fall out of the DE structure due to any muscle pathology: a reduction in the diameter of the muscle fibers, their splitting, fragmentation or other damage, reducing the number of muscle fibers in the DE or reducing the muscle volume. All this leads to a reduction (shortening) of the duration of the PDE. Therefore, in the majority of primary-muscle diseases and myasthenia gravis, stage I and II are identified, with polymyositis - first only I and II, and at recovery - III and even IV stages.

[23], [24], [25]

Amplitude of potentials of motor units

Amplitude is an auxiliary, but very important parameter in the analysis of PDE. It is measured "from peak to peak," that is, from the lowest point of the positive to the highest point of the negative peak. When registering PDEs on the screen their amplitude is determined automatically. Determine both the mean and maximum amplitude of the PDE detected in the muscle under study.

The average values of the amplitude of PDE in the proximal muscles of healthy people in most cases are 500-600 μV, in distal muscles 600-800 μV, while the maximum amplitude does not exceed 1500-1700 μV. These indicators are very arbitrary and can vary to some extent. In children aged 8-12 years, the average amplitude of the PDE is usually in the range 300-400 μV, and the maximum does not exceed 800 μV; in older children these values are 500 and 1000 μV, respectively. In facial muscles, the amplitude of PDE is much lower.

Athletes in the trained muscles register an increased amplitude of PDE. Consequently, an increase in the average amplitude of the PDE in the muscles of healthy individuals involved in sports can not be considered a pathology, since it occurs as a result of the restructuring of DEs due to a prolonged load on the muscles.

For all neurogenic diseases, the amplitude of the PDE, as a rule, increases in accordance with the increase in duration: the longer the duration of the potential, the higher its amplitude.

The most significant increase in the amplitude of PDE is observed in neuronal diseases, such as spinal amyotrophy and the effects of poliomyelitis. It serves as an additional criterion for diagnosing the neurogenic nature of muscle pathology. To an increase in the amplitude of the PDE results in the alteration of the DE in the muscle, the increase in the number of muscle fibers in the lead-out zone of the electrode, the synchronization of their activity, and the increase in the diameter of the muscle fibers.

The increase in both the mean and maximum amplitude of PDE is sometimes observed in certain primary muscular diseases, such as polymyositis, primary muscular dystrophy, dystrophic myotonia, and others.

[26], [27], [28]

Form of potentials of motor units

The form of the PDE depends on the structure of the DE, the degree of synchronization of the potentials of its muscle fibers, the position of the electrode relative to the muscle fibers of the analyzed DE and their innervation zones. The shape of the potential has no diagnostic value.

In clinical practice, the form of PDE is analyzed in terms of the number of phases and / or thorns in the potential. Each positive-negative deviation of the potential, reaching the contour and crossing it, is called the phase, and the positive-negative deviation of the potential, not reaching the isoline, is a touristic one.

A polyphase is a potential having five phases or more and crossing the center line at least four times. Potential may include additional tours that do not intersect the center line. Tours are in both the negative and the positive part of the potential.

In muscles of healthy people, PDE, as a rule, are represented by three-phase potential oscillations, however, when registering PDE in the end plate region, it can have two phases, losing its initial positive part.

Normally, the number of polyphase PDEs does not exceed 5-15%. An increase in the number of polyphase PDEs is considered as a sign of a violation of the structure of DE because of the presence of some pathological process. Polyphase and pseudopolyphase PDEs are recorded in both neuronal and axonal and primary muscular diseases.

[29], [30], [31], [32], [33]

Spontaneous activity

Under normal conditions, when the electrode is stationary, there is no electrical activity in the relaxed muscle of a healthy person. When pathology appears spontaneous activity of muscle fibers or DE. Spontaneous activity does not depend on the will of the patient, it can not stop it or cause it arbitrarily.

Spontaneous activity of muscle fibers

The spontaneous activity of muscle fibers includes fibrillation (PF) and positive acute waves (POV). PF and POC are recorded exclusively in conditions of pathology when a concentric needle electrode is introduced into the muscle. PF is the potential of a single muscle fiber, POV is a slow oscillation occurring after a rapid positive deviation, which does not have an acute negative peak. The POV reflects the participation of both one and several adjacent fibers.

The study of the spontaneous activity of muscle fibers in clinical study of the patient is the most convenient electrophysiological method, which makes it possible to judge the degree of usefulness and stability of nerve influences on muscle fibers of skeletal muscle in its pathology.

Spontaneous activity of muscle fibers can occur with any pathology of the peripheral neuromotor apparatus. In neurogenic diseases, as well as in the pathology of the synapse (myasthenia gravis and myasthenic syndromes), the spontaneous activity of muscle fibers reflects the process of their denervation. In most primary muscular diseases, the spontaneous activity of the muscle fibers reflects any damage to the muscle fibers (their cleavage, fragmentation, etc.), as well as their pathology caused by the inflammatory process (in inflammatory myopathies - polymyositis, dermatomyositis). In both cases PF and POV testify to the presence of the current process in the muscle; in the norm they are never recorded.

• The duration of the FS is 1-5 msec (it does not have any diagnostic value), and the amplitude varies very widely (on average 118 ± 114 μV). Sometimes high-amplitude (up to 2000 μV) PF are detected, usually in patients with chronic diseases. The timing of the appearance of PF depends on the site of nerve damage. In most cases, they occur 7-20 days after denervation.
• If for any reason the reinnervation of the denervated muscle fiber does not occur, it eventually dies, generating POVs, which consider EMG a sign of the death of denervated muscle fibers that have not received the innervation that they lost earlier. According to the number of PF and POV recorded in each muscle, you can indirectly judge the degree and depth of its denervation or the volume of dead muscle fibers. The duration of the PWR is from 1.5 to 70 ms (in most cases up to 10 ms). The so-called gigantic PEAs with a duration of more than 20 ms are detected with prolonged denervation of a large number of nearby muscle fibers, as well as with polymyositis. The amplitude of the CW oscillates, as a rule, in the range from 10 to 1800 μV. PWR of large amplitude and duration are more often detected in later stages of denervation ("giant" POV). The CWs begin to be recorded 16 to 30 days after the first appearance of the PF, they can persist in the muscle for several years after denervation. As a rule, in patients with inflammatory lesions of the peripheral nerves, POC are detected later than in patients with traumatic lesions.

PF and POC respond most quickly to the onset of therapy: if it is effective, the severity of PF and POC decreases after only 2 weeks. Conversely, if the treatment is ineffective or ineffective, their severity increases, which makes it possible to use analysis of PF and POC as an indicator of the effectiveness of the drugs used.

Myotonic and pseudo-photonic discharges

Myotonic and pseudo-myotonic discharges, or high-frequency discharges, also refer to the spontaneous activity of muscle fibers. Myotonic and pseudo-myotonic discharges differ in a number of features, the main of which is the high frequency of the elements constituting the discharge, that is, the high frequency of the potentials in the discharge. The term "pseudo-myotonic discharge" is increasingly replaced by the term "high-frequency discharge".

• Myotonic discharges are a phenomenon detected in patients with various forms of myotonia. When listening, it resembles the sound of a "dive bomber." On the monitor screen, these digits look like recurring potentials of gradually decreasing amplitude, with progressively increasing intervals (which causes a decrease in pitch). Myotonic discharges are sometimes observed in some forms of endocrine pathology (eg, hypothyroidism). Myotonic discharges occur either spontaneously, or after a slight contraction or mechanical stimulation of the muscle introduced into it by a needle electrode or by a simple tapping on the muscle.
• Pseudo-myotonic discharges (high-frequency discharges) are recorded in certain neuromuscular diseases, both connected and not associated with denervation of muscle fibers. They are considered a consequence of the efaptic transmission of excitation with a decrease in the insulating properties of the membrane of muscle fibers, creating a prerequisite for the propagation of excitation from one fiber to the next lying: the pacemaker of one of the fibers sets the rhythm of the impulse, which is imposed by a number of lying fibers, which explains 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. Observe pseudo-mytonic discharges in various forms of myopathy, polymyositis, denervation syndromes (in the late stages of reinnervation), with spinal and neural amyotrophies (Charcot-Marie-Tous disease), endocrine pathology, trauma or compression of the nerve and some other diseases.

Spontaneous activity of motor units

Spontaneous activity of DE is represented by potentials of fasciculations. Fasciculations are the spontaneous contractions of the whole DE, arising in a completely relaxed muscle. Their occurrence is associated with motor neuron diseases, its overloads with muscle fibers, irritation of any of its sites, functional morphological rearrangements.

The appearance of multiple potentials of fasciculations in muscles is considered one of the main signs of the defeat of spinal cord motoneurons. The exception is "benign" potential fasciculations, sometimes found in patients who complain of constant twitching in the muscles, but do not note muscle weakness and other symptoms.

Single potential fasciculations can be identified with neurogenic and even primary muscular diseases, such as myotonia, polymyositis, endocrine, metabolic and mitochondrial myopathies.

The potentials of fasciculation that arise in high-qualified athletes after debilitating physical exertion are described. They can also occur in healthy but easily excitable people, in patients with tunnel syndromes, polyneuropathies, and in the elderly. However, unlike motor neuron diseases, their number in the muscle is very small, and the parameters are usually normal.

Parameters of the potentials of fasciculation (amplitude and duration) correspond to the parameters of the PDE registered in this muscle, and can change in parallel with changes in the PDE in the course of the development of the disease.

Needle electromyography in the diagnosis of diseases of spinal cord motoneurons and peripheral nerves

With any neurogenic pathology, there is an ACE, the severity of which depends on the degree of damage to the innervation sources and on what level of the peripheral neuromotor apparatus - neuronal or axonal - a lesion occurred. In both cases, the lost function is restored due to the remaining nerve fibers, the latter beginning to branch intensively, forming numerous sprouts that go to the denervated muscle fibers. This branching has received in the literature the name "spoiting" (English "sprout" - to shoot, to branch).

There are two main types of scouting - collateral and terminal. Collateral sprighting is branching of axons in the area of Ranvier intercepts, terminal - branching of the terminal, unmyelinated axon site. It is shown that the nature of the sprighting depends on the nature of the factor that caused the disturbance of the nervous control. For example, with botulinum intoxication, branching occurs exclusively in the terminal zone, and with surgical denervation, both terminal and collateral scoring takes place.

In electromyography, these DE states at different stages of the reinnervation process are characterized by the appearance of PDE of increased amplitude and duration. The exception is the earliest stages of the bulbar form of ALS, in which the parameters of PDE for several months are within the limits of normal variations.

Electromyographic criteria for diseases of spinal cord motoneurons

• Presence of expressed potentials of fasciculations (the main criterion for lesion of spinal cord motoneurons).
• An increase in the parameters of the PDE and their polyphase, reflecting the severity of the reinnervation process.
• The appearance in the muscles of the spontaneous activity of muscle fibers - PF and POC, indicating the presence of the current denervation process.

The potentialities of fasciculations are an obligatory electrophysiological sign of the defeat of spinal cord motoneurons. 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 current process of denervation and reinnervation, when a large number of motoneurons die at the same time and the corresponding number of DEs is destroyed, the number of PEEs is increasing, their duration and amplitude are increasing. The degree of increase depends on the prescription and stage of the disease.

The severity of PF and PI depends on the severity of the pathological process and the degree of denervation of the muscle. With rapidly progressing diseases (eg, ALS), PF and POC are found in most muscles, with slowly progressing (some forms of spinal amyotrophies) in only half of the muscles, and in post-poliomyelitis syndrome in less than a third.

[34], [35], [36]

Electromyographic criteria for diseases of axons of peripheral nerves

Needle electromyography in the diagnosis of peripheral nerve diseases is an additional, but necessary method of examination, determining the degree of damage to the muscle innervated by the affected nerve. The study makes it possible to clarify the presence of signs of denervation (PF), the degree of loss of muscle fibers in the muscle (the total number of POV and the presence of giant STS), the severity of the reinnervation and its effectiveness (the degree of increase in the parameters of PDE, the maximum magnitude of the amplitude of PDE in the muscle).

The main electromyographic features of the axonal process:

• an increase in the average value of the amplitude of the PDE;
• presence of PF and STO (with the current denervation);
• an increase in the duration of the PDE (the average value may be within the limits of the norm, that is, ± 12%);
• polyphase of PDE;
• single potentials fasciculations (not in each muscle).

When lesions of axons of peripheral nerves (various polyneuropathies) also have a PSA, but its severity is significantly less than with neuronal diseases. Consequently, the PDEs are increased to a much lesser extent. Nevertheless, the main rule for changing the PDE in cases of neurogenic diseases extends to the defeat of axons of motor nerves (that is, the degree of increase in parameters of PDE and their polyphasia depend on the degree of nerve damage and the severity of reinnervation). Exceptions are pathological conditions, accompanied by rapid death of axons of motor nerves due to trauma (or some other pathological condition leading to the death of a large number of axons). In this case, the same gigantic PDEs appear (with an amplitude of more than 5000 μV), as in neuronal diseases. These PDEs are observed with long-term current forms of axonal pathology, CVD, neural amyotrophies.

If in the axonal polyneuropathies the amplitude of the PDE first increases, then during the demyelinating process with deterioration of the functional state of the muscle (by decreasing its strength), the mean values of the duration of the PDE gradually increase; much more often than in the axonal process, polyphase PDEs and potentials of fasciculations are detected and, more rarely, PF and POC.

[37], [38], [39], [40], [41], [42]

Needle electromyography in the diagnosis of synaptic and primary-muscular diseases

For synaptic and primary muscular diseases, the average duration of the PDE is typically reduced. The degree of reduction in the duration of the PDE correlates with a decrease in strength. In some cases, the parameters of the PDE are within the limits of normal deviations, and in PMD can even be increased.