The method is indispensable in identifying various diseases of the nervous system, expressed in changes in the functionality and condition of muscle fibers, in particular, myopathies, myasthenia, paresis, their differentiation from each other.
When violations of motor activity are detected, presumably connected with lesions of the nervous system in its various parts, electromyography is appointed. The study is based on the recorded bioelectric potentials, allows you to accurately determine the nature of the violation (myelinopathy, axonopathy), place, level and degree of damage to the nervous tissue.
The main objective of the study is the differential diagnosis of pathologies of the interaction system of the nervous and muscular systems: myasthenia, muscular dystrophies, diseases in which the destruction of the motor neurons of the central nervous system.
Electromyography specifies the presence of damage to the sensory fibers, signs of degeneration of nerve tissues, the reasons for reducing the mass of muscle tissue, and features of neuromuscular transmission. If damage to the nerve fibers is analyzed, their myelin sheath or axial cylinders are damaged, only the roots, the trunk of the nerve, or all of them are affected.
The study of EMG is performed using a special device – electromyograph. Its functions are to record, amplify, and evaluate impulses received from a muscle at rest and contraction.
Today there are several methods for conducting research:
- Superficial. When using this non-invasive method, electrodes are placed on the entire surface of the arms, legs, neck, other parts of the body, depending on the area of damage. It is conducted for children and patients with impaired blood viscosity. It helps to assess the condition of a large area of muscle tissue. The downside, however, is the relatively low sensitivity. Does not cause pain.
- Needle (local). It is carried out with the help of a needle electrode, which is a thin needle, which is inserted directly into muscle tissue. It is considered more informative, as the electromyograph gets in touch directly with the muscle under study. The method is invasive. Electrodes can be installed on the face to assess the functionality of the sciatic nerve and facial muscles.
- Stimulating. This type of diagnosis is carried out with the use of needle and surface electrodes, causing an uncontrolled patient to contract muscles. Used when suspected nerve conduction disturbances occur.
Only the physician determines which type of EMG for muscles to use. The choice depends on the state of health of the patient, concomitant diseases and the current diagnosis. In some cases, it is recommended to conduct joint local and superficial diagnostics.
Sometimes parallel to electromyography prescribed study – electroneuromyography. This method provides information on the speed of passage of impulses along peripheral nerves. An ENMG of the lower extremities is conducted to assess the condition of the sensory and motor fibers in connection with injuries and injuries, various forms of polyneuropathy.
Conducting electroneuromyography of the lower extremities is indicated for patients who have impaired motor activity, pain, rapid fatigue, muscle weakness, a decrease in their mass, frequent spasms, twitching, weakening of tone.
A survey was shown for suspected damage or natural dysfunction of the nervous and muscular tissue. The EMP method allows timely determination of compression of nerve fibers, the presence of injuries. Research is also carried out to control the effects of treatment.
The method is used in cardiology, neurological practice, oncology, dentistry, to clarify complex infectious diseases.
Among the main indications are noted multiple sclerosis, Parkinson’s disease, neuropathy, polio, tunnel syndrome of the upper and lower extremities. It is carried out to clarify muscular dystonia, myasthenia, the effects of injuries. The study is also shown in cases of suspected botulism, a microstroke, to determine the stage of periodontal disease; when carrying out cosmetology operations.
ENMG of the lower extremities is not performed in patients who have epilepsy, various mental disorders, and cardiac pacemakers.
A temporary contraindication is an acute period of various diseases, for example, hypertensive crisis, an attack of angina. It is not carried out in conditions accompanied by increased temperature, in the presence of wounds or other damage to the skin in those places where the installation of electrodes is expected.
The survey is postponed when it is impossible to interrupt the administration of drugs that have a strong effect on the nervous system as a whole.
Needle electroneuromyography of the lower extremities is not indicated for patients with impaired blood viscosity, as well as for those diagnosed with infectious diseases that are transmitted through blood (hepatitis, HIV).
This method is not used to diagnose people with a high pain threshold and children under eight years of age.
Research does not require adjustment of the diet. An exception is the recommendation not to eat chocolate, not to drink coffee, energy and other drinks containing caffeine, 3 hours before the procedure. Also not allowed to smoke.
Approximately six days before the procedure, the patient is asked to cancel the medication, which is directed to the neuromuscular system.
It is important for the physician to warn about the use of drugs that reduce blood viscosity, as well as about conditions that may interfere with obtaining reliable results (ARVI, exacerbation of chronic diseases).
The study is conducted in inpatient and outpatient settings. Before the procedure, the patient is asked to sign an agreement to conduct it.
The patient is seated or placed on a special chair or couch. During the EMG he can lie, sit, recline.
Places where electrodes will be installed are treated with an antiseptic, then needle or surface sensors are installed, connected to an electromyograph. The latter consists of a recording system and an amplifier. The device amplifies the received pulses a million times and registers them graphically.
The patient may experience some pain if needle-shaped electrodes are used.
To establish a more accurate diagnosis during the procedure, the person is asked to relax the muscle, then – gradually strain, at first slightly, then stronger, until the maximum stress is reached. Sometimes during the examination they ask to take a deep breath. In certain cases, EMG is shown in a state of emotional arousal.
Throughout the study, electrical impulses are recorded, which, when decoded, correspond to the relaxation time and muscle tension.
Electromyogram is displayed on paper or monitor screen. It is a graph resembling a cardiogram. When analyzing the results, the frequency of biopotentials, the magnitude of their amplitude, the nature of oscillations are taken into account.
Depending on the characteristics, four types of EMG are recorded.
The first (saturated) is a manifestation of the norm. It is characterized by fast, frequent and variable fluctuations (their frequency ranges from 50 to 100 Hz), which have a uniform pattern. At rest, the electrical activity is very small, the amplitude is low. The contraction induces rhythmic potentials with an increase in amplitude. Such an electromyogram can only be given by the normal functioning of nerve cells.
If there is a slight decrease in amplitude, they are talking about radiculoneuritis, myopathy, central paresis.
The second type is determined by reducing the frequency of oscillations (less than 50 Hz), while oscillations of different frequencies can be traced. Some – with a frequency of less than 10 Hz, others – 35 Hz. Two subtypes are defined – chastokolny and urezhenny. In general, the pattern is uniform. Such results speak in favor of damage to the nervous system at the level of neurons and nerve processes.
The third (saliate) type is characterized by sharp fluctuations with a frequency of 4 to 10 Hz. It is a sign of lesions occurring at an extrapyramidal level and manifested by changes in tone and hyperkinesis.
The fourth type is defined as “bioelectric silence”. He does not detect signs of electrical activity of the muscles, either in a relaxed state or during artificial stimulation. The results indicate the defeat of all or almost all motor neurons. It is noted for paralysis, speaks of muscle atrophy.
Each disease is characterized by its own characteristics of EMG. Thus, with neuropathies, more rare oscillations are observed, and the biopotentials have different frequencies and amplitudes. Minimal muscular activity or its complete absence is recorded when neurons die.
Spinal amyotrophy is characterized by an increase in the amplitude of oscillations, and the shape of the waves is pointed. In the voltage state, frequent high-amplitude potentials are recorded.
In myotonia, a low, high-frequency amplitude is observed during relaxation, following contraction. Signs of muscle hyper-excitability are clearly visible on the local record.
Myasthenia differs at first by normal potential, however, after prolonged voltage, the amplitude is reduced.
Parkinson’s disease is represented by rhythmic rises in amplitude. The frequency and duration depends on the location of the lesion.
Factors Affecting Results
There are several factors that can influence the results of the study, make it unreliable:
- Receiving drugs that are directed to the neuromuscular system. These include anticholinergics, muscle relaxants.
- Blood clotting disorders.
- Significant fat in the attachment points of the electrodes.
- The distance between the installed electrodes.
- The accuracy with which they are installed.
- Their direction in relation to the muscle fibers.
- Inability of the patient to follow medical instructions.
Electromyography is considered a safe procedure. Only when performing needle research sometimes a bruise occurs in the place where the puncture was made. Hematoma passes on average in a week. There is no risk of infection, since a sterile needle is used in the study. If pain persists, a compress can be made at this point. Additionally, it is recommended to take painkillers.
Electromyography is a safe informative method used to identify diseases associated with the neuromuscular system. It allows you to diagnose myasthenia, paresis, paralysis. Depending on the type of electrodes, it is invasive or non-invasive. The study clarifies the nature of the lesion, place, level, stage.
The following sources were used to prepare the article:
Gusev E. I., Konovalov A. N., Skvortsova V. I. // Neurology and Neurosurgery, ed. Konovalova A.N., Kozlova A.V. – 2014.
Lukyanov M. V Clinical electromyography. History and Prospects // Neurological Journal – 2013.
Khitrov M. V., Subbotina T. I., Yashin A. A. Electromyography as a method of objectifying the results of physical rehabilitation of injuries of the musculoskeletal system of athletes // News of Tula State University – 2012.