Your doctor prescribed you an electroneuromyogram (ENMG).
In order for you to follow the different stages without any surprises, here are some explanations:
The nerves and muscles work with very low electrical currents.
An electroneuromyogram is an examination that records the electrical activity of a muscle or a nerve. The plot obtained during the recording is a graph corresponding to the electrical activity produced by the muscles (consequences of muscle contractions) or transmitted by the nerves (nerve conduction).
The ENMG is particularly useful in certain pathologies such as myalgia (muscle pain), myasthenia gravis (extreme muscle fatigue), or certain paralysis. The qualities of rhythm, the amplitude, and the richness of the activity which are recorded are modified when there is a muscular pathology. This examination will be used to differentiate a disorder with a psychological origin from an attack of the central nervous system (brain and spinal cord). Further, there may be a disturbance in the conduction between a neuron and a muscle through the mechanism used to transmit nerve impulses to the muscle, called the motor plate.
When there is a neurogenic syndrome, which is characterized by damage to a nerve following trauma or inflammation, the electroneuromyogram makes it possible to locate the affected nerve (s) and to specify the mechanism of this pathology. The nerve consists of an axon surrounded by a myelin sheath. With the help of this examination, it is possible to differentiate the involvement of these two tissues and to know their origin. On the other hand, the electroneuromyogram makes it possible to follow the evolution of the disease and to confirm the diagnosis. However, this examination does not indicate the cause of pathologies.
With the information obtained by the electroneuromyogram, it is possible to distinguish lesions of the fibers constituting the nerves of small caliber and those of the nerves of a large caliber. Indeed, the causes being different, it also allows to know the process in question and to know if it is acute (occurred relatively quickly) or chronic (spread over time). On the other hand, the electroneuromyogram allows the monitoring and recovery of the function of the nerve conduction.
The collection of electrical activity is done by very fine electrode needles (non-hollow needles, which inject nothing) which are inserted under the skin on the path of a nerve and in contact with it. There is generally no risk of bleeding or infection, the needles being for single use, sterile in unit packaging, and discarded after each patient in special containers. When there is a contraindication to the bite (very hypo-coagulant treatment, “big arms” after surgery for breast cancer), this part of the examination is done with electrodes bonded to the surface: but the information obtained is then less specific. One electrode acts as a transmitter and another as a receiver (when measuring nerve conduction velocities and the rate of propagation of nerve impulses in a nerve).
There are two types of examinations:
The detection examination consists of recording the spontaneous electrical activity of a muscle, first at rest, then during a voluntary movement. We place an electrode on the surface of the muscle we want to study. This is shaped like a needle that is pushed through the skin to the affected muscle. The electrode is connected to a device that will reproduce on a screen and then on unrolling paper, a drawing in the form of a graph representing a succession of small waves comprising spikes. Each of them corresponds to the contraction of a muscle and more precisely to the contraction of a motor unit which corresponds to a group of muscle cells (myofibrils) controlled by a nerve cell. In the case of tetany (muscular hyperexcitability), spontaneous activity (fibrillation) is then very rich.
The stimulation exam is different. After stimulating a nerve using a painless but brief electrical current, we can see a muscular reaction appear. Depending on the individuals and the pathology involved, the speed of conduction of the influx is different. Thanks to this device, we can thus measure the speed of neuro-muscular conduction (that is to say between the nerve and the muscle), and thus have an idea of the disease in question. In other words, the measurement of nerve conduction velocities makes it possible to assess the conduction velocity.
The electroneuromyogram is performed either in a medical office or in a hospital consultation. It is performed by a neurologist. It does not require any special preparation and takes place over a period of approximately 20 to 40 minutes. First, you will have an appointment, during which you will explain your symptoms and the diseases which you may be suffering from, and for which you are taking medication. A clinical examination will complete this information. The electroneuromyogram will then be performed.
- No special preparation is necessary before the exam: you can eat and drink, take your usual medicines
- Do not put moisturiser on your body (hands, arms, legs) on the day of the exam.
- Bring the prescription, previous ENMG (even old), any operating reports related to the current pathology, x-rays, MRI, scanners, results of biological examinations, the list of drugs usually taken (certain drugs may affect the activity of nerves and muscles and affect the results).