Examinations of the functioning of the nervous system

What is it about ?

Stimulations (stimuli) in the muscles and the nervous system (the brain, spinal cord and nerves) are caused by small electrical currents. This electrical activity can be measured and viewed on a graph. It is the subject of a medical specialty, neurophysiology. It is an important aid in diagnosing a disease of the muscles or the nervous system. It is also used to determine the activity of the brain, for example in a person in a coma.

Some important techniques in neurophysiology

• THE’EEG (electroencephalogram) is a test that measures the electrical activity of the brain. To record it, about twenty electrodes are placed on the head. A gel ensures contact between the skin and the electrode. EEG is used for:
• may notice local or global abnormalities in the brain, including epilepsy, inflammation of the brain (encephalitis) and other brain conditions such as certain forms of dementia, delirium, poisoning, etc. ;
• distinguish between different types of epilepsy and assess the course, for example with a long-lasting seizure;
• see the effects of a baby’s lack of oxygen during childbirth;
• get a feel for the depth of general anesthesia.
• THE’ENMG or EMG (electroneuromyography or electromyography) is a test that examines the function of the nerves that are outside the brain and spinal cord (peripheral nerves), the connection between nerves and muscles, and muscle cells. The examination provides information on the central nervous system (brain and spinal cord).
• ENMG is mainly used in cases of disturbance or loss of function, for example in case of loss of sensitivity, loss of pain sensation, loss of strength or in case of paralysis. In addition to the lesion, it is also often possible to determine the localization precisely. For example, in the event of tingling in the fingers, the ENMG makes it possible to know if the cause is at the level of the wrist, the elbow, the armpit or the vertebrae of the neck.
• This examination is recommended when the doctor suspects:
• nerve compression (compression of a nerve that no longer conducts nerve impulses);
• damage to a nerve coming out of the spinal cord (nerve root);
• inflammation of a nerve;
• a disease that affects nerve fibers.
• In addition, this technique also makes it possible to carry out a neurography, which measures the rate of progression of nerve impulses in nerve fibers. In nerve compression, the speed decreases as the impulse passes through the place where the nerve is compressed.
• ENMG has three drawbacks:
• The lesion must have been present for at least three weeks before abnormalities can be detected
• The exam is unpleasant because fine needles have to be placed along the path of the nerve.
• Completing this exam is a tedious task.
• THE’quantitative sensory assessment (QST) can detect abnormalities of small nerve fibers responsible for the sensation of heat, cold and pain. This test is performed in cases of chronic pain when other examinations have not provided a definitive answer.
• The exam measuring the evoked potentials may show damage to the sheath (myelin) that protects the nerve fibers. This sheath is destroyed in conditions like multiple sclerosis (MS).
• In the event of a sleep disorder, if the patient’s history and discussions with him or in particular a sleep diary do not make it possible to determine the cause, a neurophysiological examination may be useful in the context of a sleep study (polysomnography). There are different kinds of tests to determine the cause (s) of insomnia.
• To study the structure of sleep, the polysomnography uses several techniques, such as the measurement of respiration and oxygen saturation, EEG (see above), eye measurements, video recordings… For this, you must spend a night in the hospital.
• The limited nocturnal polygraphy makes different recordings to assess problems occurring during sleep, such as snoring, restless legs, frequent awakenings, etc.
• the iterative sleep onset latency test (TILE or MSLT) and the wakefulness test (TME or MWT) measure alertness and can be helpful in seeing fatigue during the day.
• THE’actigraphy records activities and movements over several days and thus allows documentation of sleep-wake rhythm, insomnia and fatigue.

Want to know more?

• Electromyography – Erasme Hospital
• Evoked potentials – Erasme Hospital
• Your hospitalization at the sleep laboratory – Hôpital Erasme UL

• The electroencephalogram explained to children – Plaster

Source

Foreign clinical practice guide ‘Diagnostic clinical neurophysiology’ (2000), updated on 08/28/2017 and adapted to the Belgian context on 12/01/2019 – ebpracticenet