Electromyography( EMG) - Causes, symptoms and treatment. MF.

Electromyography is the diagnosis of bioelectric potentials in muscle when muscle fibers are excited( contracted).For the first time on the person used electromyography in 1907 the German scientist G. Piper. At present, the electromyograph is a computer system that records biopotentials, amplifies them, calculates the amplitude, frequency and duration of latent periods, reduces "noise", conducts stimulation and analysis.

Potentials are recorded using dermal or needle electrodes.

Electrodes

Needle electromyography

Further the signal is amplified, processed by an electromyograph and transmitted to a visualization device - either on an oscillograph for recording on paper or on a magnetic medium - an electromyogram is recorded. The amplitude of the oscillation of the muscle potential is estimated.

The main types of electromyograms .

The work of the muscles depends on the quality of the muscle fibers themselves and on the full work of the nerves that conduct a nervous impulse from the spinal cord and brain. By disturbing the electrical activity of muscles, one can judge the existing disease with the pathology of muscle tissue, determine the cause of weakness( paralysis) of the muscle, its jerking.

The diagnostic method is harmless. There may be a slight soreness in the place where the needle electrode is inserted.

Indications of electromyography:

- complaints of pain and muscle weakness, muscle slimming, muscle spasms, muscle twitching and muscle cramps,
- suspected myopathy, myasthenia, myotonia, amyotrophic lateral sclerosis, myoclonus, muscular dystonia, essential tremor, Parkinsonian syndrome, multiple sclerosis,
- traumas of peripheral nerves and plexuses, lesion of roots in degenerative - dystrophic spine pathology, facial nerve neuropathy, polyneuropathy, polymyositis, tnnelnye syndromes
- for assessing the functional state of the dynamics and effectiveness of treatment,
- local myography performed for accurate administration of Botox in spastic muscle fibers.

How to conduct EMG

It is not recommended to conduct a study after taking medications( muscle relaxants, anticholinergics) and physiotherapy procedures, smoking and consuming caffeine( coffee, chocolate, tea, cola).If you have a pacemaker, you are taking anticoagulants, you must tell your doctor about it.

The study is conducted in a relaxed state - lying or sitting. First, remove the potentials at rest, then with a slow muscle strain. The dermal electrodes record the general indications from the muscle( interference, global EMG), the needle is injected into different parts of the muscle, different muscles( local EMG).

The study uses electrical muscle stimulation. Cumulative electrodes are paired metal plates up to 10.5 mm in size, which are superimposed at a distance of 20-25 mm from each other. For electrostimulation, surface stimulating electrodes are used. Muscle muscles are symmetrical, functionally related to each other, at maximum stress.

Depending on the purpose of the survey, the procedure can last from 15 minutes to an hour.

At rest, with maximum relaxation, biopotentials are not recorded.

Explanation of EMG

At the onset of muscle contraction, oscillations with an amplitude of 100-150 μV appear, with a maximum reduction of 1000-3000 μV( depending on the person's age and physical development).

In the primary muscular disease - myositis, progressive muscular dystrophies, a decrease in the amplitude of the oscillations is recorded. The decrease in the amplitude correlates according to the severity of the muscle damage - in severe cases up to 20-150 μV with maximum excitation, and with slowly progressing course of the disease and in the initial stages - up to 500 μV.With a local EMG, a normal total number of action potentials is recorded, but the amplitude and duration are reduced. This is due to a decrease in the number of normal muscle fibers, capable of contraction. To compensate for the muscle defect in the body, more muscles are activated. This causes an increase in interference and the number of polyphase( multiphase) potentials.

In cases of lesions of peripheral nerve trunks of ( hereditary, metabolic( including diabetic), toxic( including alcoholic) polyneuropathies), the global EMG records a decrease in the oscillations, unequal amplitude and frequency single potentials. The general background of EMG is characterized by low-amplitude activity. On the local EMG, polyphase action potentials with practically normal characteristics are recorded. When most of the nerve fibers die, the bioelectrical activity of the muscles is gradually inhibited to complete bioelectric silence - there are no potentials.

With spinal amyotrophies - hereditary diseases of spinal cord motoneurons with muscle weakness, muscle twitching at local EMG, spontaneous activity in the form of potentials of fibrillation, acute waves, increase in amplitude is recorded. Global EMG registers at rest spontaneous bioelectrical activity( fasciculation 100 - 400 microvolts), and at maximum voltage the high amplitude rhythmic potential is the "rhythm of the stockade".

With myotonic syndromes - a group of hereditary diseases with delayed muscle relaxation( dystrophic myotonia, myotonia Thomsen, Becker, Eilenburg. ..), the muscles are easily excitable and the myotonic aftereffect is recorded on the EMG: low-amplitude, high-frequency electrical activity for a long time after the termination of voluntary muscle contraction withslow gradual fading. On local EMG with myotonia, the increased excitability of muscle fibers is recorded - a series of action potentials of equal amplitude in response to the introduction of a needle electrode.

In cases of myasthenic syndromes - a violation of neuromuscular synaptic transmission on EMG, an increasing decrease in the amplitude of the evoked muscular potential is recorded with repeated rhythmic stimulation.

In Parkinsonism, the essential tremor of , the pathology of supra-segmental effects on the motor horn of the anterior horns of the spinal cord, the interest of the extrapyramidal system on the global EMG, rhythmically repeated "volleys" of spindle-like increase in the amplitude of the oscillations and subsequent reduction are recorded. The frequency and duration of the "spindles" varies depending on the localization of the pathological process.
For more accurate diagnosis, a joint study is used - electromyography with electroneurography - electroneurography.

Doctor neurologist Kobzeva S.V.