Electromyography is an additional examination method for sciatica that provides data on damage caused by disc herniation, and it is differentially diagnostically significant compared to other diseases. EMG clinically means the recording of electrical activity in a muscle. Different methods are applied in order to obtain information about the continuity, that is, the lack of continuity in the so-called motor unit (the motor unit consists of a cell in the anterior horn of the spinal cord, a motor axon or neurite, a motor plate and muscle fibers innervated by that axon).
Electromyography helps us to explain muscle weakness caused by nerve or muscle damage. It also reveals to us the extent of damage to the motor nerve due to such an impact, the course of reinnervation, and thus the success of the treatment. It also shows us the location of the damage, at what height it occurred, and whether it is getting worse or better.
The metal disk of one electrode is attached to a certain place, and the very thin needle of the other electrode is inserted into the muscle that we want to examine, and we record the electrical activity between those two places.
Most often we use the so-called coaxial needle electrode that enables testing of the motor unit. In a narrow tube (cannula), similar to an injection needle, the wire is made of platinum, and the electrical potentials are established between the cannula and the wire. The electrode is connected to an electrograph which is, in fact, a differential amplifier equipped with a cathode ray tube (oscilloscope) for visual display of the detected and amplified electrical potentials.
In a healthy and relaxed (relaxed) muscle, there is electrical peace, which means that there are no bioelectrical potentials. Objective proof of the existence of nerve damage (denervation) is the appearance of special electrical potentials in a relaxed muscle. We can expect their appearance already on the fifth day after nerve damage, and most often we notice it in the second to third week. Changes in the electromyographic curve during voluntary muscle contraction are different when the peripheral nerve of the muscle is damaged and are directly proportional to the extent of the damage. We also measure the speed of conduction of electrical impulses in the affected segments that degenerate, but it is usually normal in the first days after nerve damage. If the nerve damage is only partial, as is most often the case with nerve damage due to a hernia, the conduction velocity is normal. Electromyography is slightly painful for the patient and is easily tolerated by patients.
There is no doubt that EMG is only an auxiliary diagnostic method, but the data obtained with it are very important. We emphasize, however, that the clinical picture, along with other diagnostic methods, is crucial for making correct conclusions, especially regarding the method of treatment. Electromyography is very useful when we are not sure about the nature of the disease, especially if we are not sure whether it is a tumor inside the sheaths of the spinal cord or pressure on the nerve root due to a herniated disc. We have to repeat the EMG several times in order to get an answer about the course of the disease, and especially to see what the prognosis is for recovery. Namely, with this method, we discover the previous success or failure of the applied therapy, sometimes long before other signs show it.
The data we get with electromyography is very valuable, and that’s why we believe that this method should be used.
