Electromyography

A diagnostic technique that allows you to examine the musculature system by recording electrical muscle potentials is called electromyography. The procedure helps to assess the functionality and condition of the skeletal musculature and peripheral nerve endings. Electromyography makes it possible to identify the pathological focus, determine the extent of its spread, the degree and type of tissue damage. [1]

Physical basis of electromyography

A muscle that remains in a maximally relaxed state has no bioelectric activity. On the background of weak contractile activity there are neural oscillations - oscillations with amplitude from 100 to 150 μV. The ultimate voluntary contraction of musculature can be manifested by different oscillatory amplitude, which is individual depending on the age and physical category of a person: on average, the maximum value usually reaches 1-3 mV.

It is accepted to distinguish between spontaneous electrical activity of muscles and electrically conditioned muscle reactions (action potentials) arising as a result of artificial external influence of an impulse on a muscle or as a result of a natural internal volitional signal. The external influence is understood to be both mechanical (e.g., hammer stimulus on a muscle tendon) and electrical.

The term "electromyogram" means a curve of fixation of electrical muscle activity. To record temporal changes of potential difference, a special device - electromyograph - is used.

The most popular study of motor fiber conduction is M-response recording. [2]

M-response electromyography

The M-response refers to evoked muscle potentials, which are the total synchronous discharge of the innervation factor in response to electrical excitation of a nerve. As a rule, the M-response is recorded with the use of skin electrodes.

In determining this index, attention is paid to the severity of threshold stimulation, the latent period of evoked potentials, as well as its type, duration, amplitude, and, in general, to the combination of these values.

The M-response threshold, i.e. The threshold of excitability, the minimum electrical stimulus, is recorded. A strong increase in this indicator is noted when a muscle or nerve is affected, but a decrease is very rarely observed.

Additionally, the intensity of the stimulus leading to an M-response of maximum amplitude is assessed.

In describing the type of muscle action potential, the characteristics of monophasic (deviates from the isoline in one direction), biphasic (deviates from the isoline in one direction, then the other), and polyphasic (three-, four-, or more) are used.

The amplitude of the M-response is determined from negative to positive vertex, or from negative vertex to isoline. The ratio between the highest and lowest amplitude is often analyzed (dissociation may be noted in some states).

The duration of the M-response is estimated in milliseconds as the period of the pulse oscillation from the first deviation from the isoline to its return to the isoline. The index is determined most often when the nerve is stimulated at the most distal point. [3]

Indications for the procedure

Electromyography provides information both about the state of an individual muscle and about the CNS as a whole - about the state of the spinal cord and brain. This is due to the fact that brain structures control motor skills by sending signals to the muscles.

Electromyography is used not only for pathologies, but also for physiological assessment of motor function, determination of the degree of fatigue, and for many other purposes. In the course of electrodynamic diagnostics, the standard application of electrodes attached to the muscle under study. With the help of multichannel electromyography, the work of several muscle groups is recorded simultaneously.

Psychologists use this diagnostic procedure to record mimic muscle potentials. Speech specificity is studied by the method of evaluation of lower lip potentials. Recorded electromyograms of speech indicate that the internal-speech mechanics is built according to the principle of feedback. After the thought of reproducing a sound is produced, the speech organs begin to move. In turn, these movements affect brain structures. Electrical values also reflect so-called "mute speech", e.g., there is a correlation between utterances "to oneself" and the muscle potentials of the vocal cords. [4]

Indications for conducting, in which diseases electromyography is prescribed, the doctor determines. Most often it is about such pathologies:

• pain, spasms, abrupt weakening, convulsive twitching of muscles (one or more muscle groups);
• Parkinson's disease;
• multiple sclerosis;
• Traumatic injuries involving peripheral nerve fibers, spinal cord and brain structures;
• Polyneuropathy, consequences of polio;
• tunnel syndrome;
• facial nerve neuropathy;
• myasthenia gravis;
• Polymyositis, muscle tone disorders;
• microstrokes;
• botulism.

Electromyography in myasthenia gravis is often used repeatedly: as part of the diagnosis, as well as to assess the dynamics of ongoing treatment.

It is appropriate to use local electromyography before cosmetic procedures - in particular, to clarify the areas of Botox injections.

Electromyography is also used to determine the degree of myodystrophy and for differential diagnosis between primary (muscular) and secondary (neural) myodystrophy. The procedure is considered safe and at the same time very informative, it is well tolerated both by elderly patients and children. This allows this type of diagnosis to be used in neuropathologic, cardiologic, infectious disease, and oncologic practice.

Preparation

Electromyography does not require any special preparation. It is only necessary to pay attention to the following nuances:

• If the patient is taking medications that affect the state and operation of the neuromuscular apparatus (e.g., antispasmodics, myorelaxant group drugs, anticholinergics), the treatment should be suspended about 4-5 days before the scheduled electromyography.
• If the patient takes medications that affect the quality of blood coagulation (anticoagulants, etc.), it is necessary to warn the doctor in advance.
• No alcohol should be taken 3 days before the study.
• For 3 hours before the diagnosis should not smoke, drink stimulating drinks (coffee, tea), treat the skin at the site of the procedure with any creams and ointments, hypothermia.

The choice of electromyography method and the extent of diagnostic measures is determined by the doctor, which depends on what diagnosis is suspected.

When going for diagnosis, the patient should take a referral from the attending physician.

Technique of the electromyography

The electromyography procedure is performed on an outpatient basis. On average, it lasts about 40-45 minutes.

The patient is asked to remove his/her clothes (usually partially), lie down or sit on a special couch. The examined area of the body is treated with antiseptic, after which electrodes connected to the electromyograph apparatus are applied to the skin (glued with a plaster) or injected intramuscularly. Stimuli are applied with the necessary current strength, depending on the depth of localization of the nerve. When conducting needle electromyography, electric current is not used. The specialist registers muscle biopotentials first at the moment of relaxation, then - in a state of slow tension. Biopotential impulses are visualized on a computer screen and also recorded on a special carrier in the form of a wavy or tooth-shaped curve (similar to an electrocardiogram).

The specialist transcribes the indicators immediately after the procedure is performed.

Classification of electromyography

The term electromyography can be used broadly to refer to numerous types of myographic techniques - including needle EMG, global EMG, and stimulation studies. [5] Most commonly, these types of diagnostics are referred to:

• Interference electromyography (also known as surface or percutaneous electromyography) is the recording and evaluation of muscle biopotentials in the state of rest or voluntary tension by withdrawing bioelectrical activity with external electrodes from the surface of the skin over the motor point. The technique is non-invasive, painless, and helps to generally assess electrical muscle activity.
• Electromyography with needle electrodes refers to invasive diagnostic methods: using the thinnest disposable electrode, the specialist can detect electrical muscle activity both in a calm (relaxed) and tense state. During the diagnostic process, the doctor injects the electrode intramuscularly, which is accompanied by a slight painful sensation (as when performing an intramuscular injection). Needle electromyography is more often used to examine patients with pathologies of peripheral motor neurons (amyotrophic lateral sclerosis, spinal muscular atrophy) and muscles (dystrophic processes, polymyositis and myopathies).
• Stimulation electromyography is a non-invasive diagnostic method that uses superficial surface electrodes to determine the degree of impulse conduction along nerve fibers due to electrical stimulation. During the procedure, the patient feels tingling in the area of current influence, as well as twitching (involuntary contractions) of the examined muscle group. Most often, stimulation surface electromyography is prescribed for pathologies of peripheral nerves (polyneuropathies, neuropathies) and disorders of neuromuscular communication (decrement test).

Electromyography in dentistry

Electromyography is used to study the neuromuscular apparatus by recording the electrical potentials of the masticatory muscles, which helps to clarify the features of the function of the dento-mandibular mechanism.

Electrical activity of the masticatory muscles is recorded on both sides. To withdraw biological potentials, surface electrodes are used, which are fixed in the area of motor points - in the areas of extreme muscle tension, which is determined by palpation. [6]

Functional samples are used for registration:

• when the mandible is physiologically calm;
• while the jaws are clenched in their usual position;
• during arbitrary and given chewing movements.
• Electromyography is repeated at the end of treatment to assess the dynamics.

Electromyography of evoked potentials

The technique of evoked potentials provides objective information about the state of central and peripheral components of various sensitive systems: visual, auditory, and tactile organs. The procedure is based on fixation of electrical brain potentials to external stimuli - in particular, to the presentation of visual, auditory, tactile stimuli. [7]

Evoked potentials are categorized into:

• visual (reactions to light flash and checkerboard pattern);
• auditory stem cells;
• somatosensory (reactions to stimulation of nerves in the extremities).

The above techniques are used mainly to investigate demyelinating pathologies of the central nervous system, preclinical course of multiple sclerosis, as well as to determine the extent and degree of lesions in cervical cerebrospinal cord and brachial plexus injuries. [8]

Electromyography of the extremities

Electromyography of the muscles of the lower extremities is performed:

• for numbness, tingling, chilliness in the legs;
• for shaky knees, leg fatigue;
• in the emaciation of certain muscle groups;
• in endocrine disorders (type 2 diabetes mellitus, hypothyroidism);
• for lower extremity injuries.

Electromyography of the upper extremity muscles is indicated:

• when numbness in the hands (especially at night, when a person has to wake up several times and "develop" the numb limb);
• with increased hand sensitivity to cold;
• with tingling in the palms, tremors;
• when there is weakness and a marked decrease in the volume of the muscles of the upper limb;
• Injuries involving nerve and/or muscle damage. [9]

Facial electromyography

It is often necessary to examine the nerve and muscle apparatus localized in the facial area - in particular, in the case of masticatory muscles, trigeminal or facial nerve pathology. In such a situation, the use of electromyograph is indicated, directing electrical impulses, reading them and analyzing the information obtained. In this case, diseases affecting the mimic and masticatory muscles, temporomandibular joint, neuromuscular transmission can be accurately identified.

Electromyography of masticatory muscles is successfully used to diagnose muscle spasms, signs of muscular atrophy, pain and tension sensations in the face, cheekbones, jaw, temples. The study is often recommended for people with traumatic injuries, after surgical interventions, strokes, paralysis. [10]

Pelvic floor examination

Electromyography of pelvic floor muscles is successfully used in coloproctology, urology, gynecology, as well as in gastroenterological and neurological practice.

Bladder electromyography includes a needle procedure with quantification of motor unit potentials, which allows the diagnosis of denervation-reinnervation pathology in the pelvic floor musculature.

Electromyography of the penile nerve makes it possible to assess the preservation of nerve innervation. A stimulation procedure is performed using a special electrode and analyzing the latency of the M-response and late ENMG-phenomena. The M-response reflects the state of conduction along the distal region of the efferent pathway, and late ENMG-phenomena indicate the state of conduction mainly along the afferent pathway. The bulbocavernosal reflex, which occurs as a reaction to electrical stimulation of sensitive areas of the penile nerve, is also studied. Somatosensory evoked potentials are evaluated.

Electromyography of the anal sphincter allows us to assess the viability and functional activity of the corresponding muscle groups.

Electromyography of the perineal muscles determines cutaneous sympathetic evoked potentials, analyzes the latency of the provoked motor response from the perineal muscles during spinal and/or cortical magnetic stimulation. [11]

Electromyography of the cervical muscles

Electromyographic study of the spine allows you to identify many pathologies caused by disorders of the muscular system (dystrophic processes) and nerves (sclerosis, peripheral neuropathy). [12] Diagnosis is used:

• Before treating osteochondrosis, intervertebral hernias;
• to assess spinal musculature;
• for the study of higher nervous activity;
• to determine the possibility of recovery from injuries or congenital abnormalities of the cervical muscles;
• to identify the underlying causes of muscle weakness, paralysis, myasthenia gravis, etc.

It is also important to understand that electromyography is not capable of detecting problems directly in the spinal cord or brain, but can only examine the condition of nerve and muscle fibers.

Electromyography of respiratory muscles

Diagnosis may include evaluation of the functionality of the diaphragm, sternoclavicular-papillary, pectoralis major, and rectus abdominis muscles. Signals stimulated include:

• Diaphragm (electrodes are placed in the area of the 6-7 intercostal space on the right side at the level of the outer edge of the rectus abdominis muscle).
• Large pectoral muscle (electrodes are placed on the right side on the midclavicular line at 3-4 intercostal intervals, and in female patients - one interval higher).
• Sternoclavicular-papillary muscle (electrodes are placed 2-3 cm above the clavicle).
• The rectus abdominis muscle (electrodes are fixed 3 cm lateral and below the umbilical opening.

During the study, the patient sits completely relaxed. [13] Readings are recorded:

• in a moment of calm breathing;
• with frequent inhalations and exhalations;
• at a time of high pulmonary ventilation.

Electromyography on a child

One of the most informative and practical techniques for diagnosing neuropathologies in children is electromyography. The procedure helps to assess the bioelectrical activity of the muscular and nervous system, to determine the degree of damage to the nerve mechanism as a whole and to check the condition of individual muscles. Thanks to electromyography, it is possible to clarify the location of nerve damage, find out the cause of paralysis, excessive neurosensitivity or atrophic process.

Diagnostic testing is indicated:

• if the child complains of seizures, spastic attacks, weakness of individual muscle groups;
• If there is impaired defecation or urination;
• children with cerebral palsy or other motor disorders;
• If the child has pain syndrome, sensory disturbances, limited muscle weakness.

Superficial electromyography can be performed on children from the first day of life. However, parents should be prepared that the procedure may last more than half an hour. During this time, it is necessary to keep the baby on the couch so as not to disturb the position of the electrodes of the myograph. The diagnosis is painless and absolutely safe for the child, and the results obtained are really valuable and informative. [14]

Contraindications to the procedure

As such, electromyography has no contraindications. Exceptions include superficial tissue damage in the area of the proposed procedure (as a result of trauma, skin infection, etc.), psychopathology, epilepsy, insufficient blood coagulation.

In addition, electromyography becomes impossible if the patient has a pacemaker, or if the area under examination is covered with a plaster bandage, bandage without the possibility of removing it.

There are some limitations of electromyography as well:

• diagnosis does not allow to investigate the state of autonomic and fine sensitive nerve fibers;
• methodological difficulties may arise during the diagnostic process;
• in the acute phase of the pathologic process electromyographic changes often lag behind the clinical symptoms (therefore, in the acute course of neuropathy, regardless of the etiology of the disease, electromyography should preferably be performed not earlier than 15-20 days after the first pathologic signs appear);
• It may be difficult to examine edematous areas, areas with trophic changes, and obese patients.

Normal performance

The results of electromyography are formalized in the form of a protocol, which reflects the results of the examination. On the basis of the indicators, the doctor draws up a diagnostic conclusion, called electrophysiological diagnosis. At the next stage, this protocol goes to the treating specialist, who compares it with the patient's complaints, existing objective pathological signs, the results of laboratory and instrumental diagnostics, and then makes a final diagnosis.

During needle electromyography, electrical muscle activity is recorded at rest and during contraction. It is considered normal if the muscle at rest does not reveal any electrical activity, and in the state of minimal contraction there are effective potentials of isolated motor elements. Against the background of muscle contraction intensification, the number of active elements increases, and an interference pattern is formed.

Denervation of muscle fibers is determined by increased activity during needle insertion, as well as by pathological spontaneous activity (fibrillations and fascioculations). Fewer motor elements are involved in the contractile process, and a reduced interference pattern is formed. Preserved axons innervate nearby muscle fibers, enlarge motor elements, which leads to fixation of giant action potentials. [15]

In primary musculature lesions, limited fibers are affected without spreading to motor elements: signal amplitude is reduced, interference pattern is unchanged.

To assess impulse conduction velocity, electrical stimulation of the peripheral nerve is performed at various points, measuring the time period until the moment of muscle contraction. The term required to conduct an impulse over a certain distance is defined as the rate of excitation propagation. The term of impulse travel from the near point of excitation directly to the muscle is referred to as distal latency. The rapidity of impulse conduction is determined in relation to large, myelinated fibers. Insufficiently myelinated or unmyelinated fibers are not evaluated.

In patients with neuropathies, impulse conduction velocity is reduced, and the muscle response is dissociated due to potential dispersion (potentials propagate along axons with a heterogeneous degree of damage). [16]

Complications after the procedure

There are usually no adverse effects from electromyography. If the procedure is performed by a competent and experienced specialist, it is considered completely safe and does not cause complications.

During the diagnostic examination, a person may experience a slight tingling sensation associated with the delivery of electrical vibrations. In addition, a slight soreness may accompany the moment of insertion of the needle electrode. These sensations can not be called painful: it is a slight discomfort, so most people tolerate the study well.

The probability of complications after electromyography diagnostic procedure is considered to be negligible. Only in exceptional cases, a hematoma may form in the area of needle electrodes insertion or nerve damage may occur. There are also some isolated cases of lung damage and pneumothorax development when performing needle electromyography of the thoracic muscles.

If the patient suffers from hematologic pathologies, insufficient blood coagulation, a tendency to hemorrhage, or takes medications that inhibit coagulation, he should warn the doctor about this long before the diagnosis.

Care after the procedure

In most cases, no special care and recovery measures are required after electromyography is performed.

A doctor's help may be needed if effects such as:

• swelling, swelling of the area under examination;
• hematoma, joint dysfunction;
• increased body temperature, discharge from needle electrode insertion sites.

If these symptoms of infection appear, it is not advisable to try to treat them yourself. It is necessary to contact the attending doctor.

Testimonials

Most patients report a slight discomfort during the procedure. However, its informativeness really allows you to make a correct diagnosis, so it is better not to avoid diagnosis, but, if indicated, to perform it in a timely manner. What gives electromyography:

• helps to assess the functionality of the sensory fibers of peripheral nerves;
• helps to clarify the quality of function of motor fibers of peripheral nerves;
• allows to clarify the extent of the muscle tissue lesion (if a needle electrode is used);
• contributes to analyzing the data obtained and writing the conclusion.

The conclusion consists of the specified localization, degree, pathogenetic affiliation of the affected focus.

Electromyography is a necessary procedure when muscle or peripheral nerve pathology is suspected. For example, the diagnosis is very important if the doctor assumes that the patient has:

• nerve impingement, tunnel neuropathy;
• diffuse post-toxic or post-inflammatory nerve damage;
• trauma to the nerve, compression by a herniated disc;
• facial neuropathy;
• pathological fatigue (myasthenic syndrome, myasthenia gravis);
• motor neuron lesions in the anterior horns of the spinal cord;
• isolated muscle lesions (myopathies, myositis).

Electromyography, although it is not the "gold standard" for diagnosing all neuropathologies, but it is often this procedure that makes it possible to recognize the disease in time and start treatment early. This, in turn, will definitely lead to a positive result.