Electroenography( ENG) - Causes, symptoms and treatment. MF.

Electro-neurology is a method for studying the speed of carrying out an electrical pulse along the nerves.

It is common knowledge that the central nervous system is connected with organs of performers, including muscles, by means of peripheral nerves. On the nerves are signals to the brain and spinal cord and vice versa, signals of "control" go from the brain to the periphery.

Electroyneurography reveals peripheral nerve damage, the level and nature of the lesion( neuropathic or myopathic), the mechanism of damage( demyelination, axonal lesion), the prevalence of the lesion, the degree of lesion, determines the acute or chronic type of course of the pathological process.

Indications for END

ENN is performed with suspicion of neuropathy and polyneuropathy( diabetic, toxic, alcoholic, traumatic), demyelinating disease, amyotrophic lateral sclerosis, myasthenia gravis, muscular dystrophy, traumatic nerve damage, vertebrogenic root damage, tunnel syndrome. ENN is performed to monitor the effectiveness of treatment and progression - regression of the disease.

For more qualitative research, a joint electromyographic and electroneurographic diagnosis is carried out - ENMG.

Preparation for ENT

Before the study within 3-5 days you should not take drugs that affect the nervous and muscular system - anticholinesterase drugs, muscle relaxants, tranquilizers. Within 3 hours to exclude smoking, taking caffeine-containing products - tea, coffee, cola. The presence of a pacemaker, taking medications that affect blood clotting should be reported to the doctor.

Conducting END

For electroneurography, a metal disk-electrode is applied to the skin in the zone of innervation of the nerve under investigation, it is fixed and electric signals are applied to it. On the muscle innervated by this nerve, an electrode is also applied.

When the signal passes, the muscle is shortened. The rate of transmission of the electric pulse along the nerve to the muscle is measured. The same research is conducted on the opposite side and the results are compared. Standard methods of investigation are performed, and additional ones are F-wave, H-reflex, repeated stimulation. The speed of carrying out an electric pulse along a nerve is determined - one nerve is stimulated at different points. Rhythmic stimulation of the nerve is used to determine the functional state, for example, detecting the myasthenic or myotonic reaction;to study the speed of propagation of excitation along the nerves, their motor and sensitive fibers, to evaluate neuromuscular transmission and parameters of motor and reflex responses to nerve irritation. Normally, the speed of movement along motor fibers is lower than in sensory fibers. The amplitude, shape, swing amplitude, duration and speed are important for interpreting the data obtained.

ENG can last from 15 minutes to an hour. The scope of the study depends on the preliminary diagnosis. Thus, with traumatic neuropathy of the radial nerve, the radial nerve is examined, and with brachioplexitis all the nerves of the limb are examined.

ENG is a safe method of investigation. When the electric pulse is applied, a small discomfort is possible, although when using needle electrodes, the sensations can be from small unpleasant to severe pains - the electrodes are located at the nerve exit points, and the irritation of these points is painful in itself, each person has an individual sensitivity, pain threshold. The perception of the electrical stimulus depends on the pathology of the nerve. Needle ENG is a more accurate technique.

Evaluation of the nerve conduction

Decoding of the results of the END

When the peripheral nerve trunk is damaged, the clearest ENMG changes are recorded: a marked decrease in the velocity of impulses along both the sensory and motor nerves, a decrease in the amplitude of the action potential of the affected nerve and the response of the innervated muscles-they are stretched over timeand changed in form. In axonal damage, the rate decreases insignificantly, the amplitude of the M-response and the action potential of the nerve are reduced to a greater degree. With demyelination, the rates of excitation propagation change more( the norm for the motor nerves of the hands is 50-80 m / s, for the legs 40-60 m / s, for sensitive ones 10-15 m / s higher).With tunnel syndromes, the speed of the nerve distal to the tunnel is disturbed.

When the anterior horn of the spinal cord is affected, segmental lesion of the spinal cord, a dissociated decrease in the amplitude of the maximal muscular responses( m-response) is recorded until it is detected( M-response rate at arms 10-20 mV, legs 6-10 mV) and a sharp decreasenumber of functioning motor units, the value of the speed of the impulse and the amplitude of the caused nerve biopotentials is normal or increased. The absence of an M-response indicates gross degenerative axonal lesions.

Electro neurography at present is a complex computer apparatus that records the speed of the pulse, the amplitude of the muscle response, the potential of the action of the nerve, calculates the data and gives an analysis. By the ratio of these parameters, an experienced physician of functional diagnostics helps to clarify the diagnosis.

ENG does not make a diagnosis, but describes the changes in the work of the neuromuscular apparatus, characteristic of various pathological processes and helps the doctor-neurologist. The diagnosis of the disease is based on a combination of objective clinical data and the results of neuroimaging.

Doctor neurologist Kobzeva S.V.