Electromyogram
What does this exam correspond to?
The electromyogram (often noted EMG), is a functional exploration, which allows to assess the functioning of nerves and muscles.
It consists in applying a weak electric current to the nerve fibers, sensitive or motor, of the peripheral nervous system. This weak current (a few thousandths of an Ampere [1] ) applied for a very short time (from one thousandth to one tenth of a second) causes an artificial nerve impulse and therefore the transmission of a message along the nerve fiber.
The response to nerve impulses is recorded by sensors placed on the skin, in the form of nerve or muscle potentials (electrical currents in the nerves or muscles), transmitted to a computer.
[1] 'unit of measurement of the International System of Units for the Strength of Electric Current.
What is an EMG for?
The electromyogram is a very useful examination for the diagnosis of various diseases, including:
-
Nerve damage associated with an accident or trauma, to precisely determine the location, nature and extent of the damage.
-
Peripheral neuropathies, to define the type of neuropathy and direct towards the cause. Neuropathies can indeed have multiple origins, such as an infection, a systemic disease, nutritional deficiencies, diabetes , exposure to toxic substances, a genetic disease (Charcot disease) or even an autoimmune origin. In neuropathies, the speed of conduction of nerve impulses is reduced in the areas concerned.
-
Diseases affecting the motor neurons (motor nerve cells in the spinal cord).
-
Myasthenia gravis is characterized by a decrease in muscle response during repetitive stimulation tests.
-
Myopathies (muscle dysfunction).