Pain
In electroneurography, nerves are stimulated by small electrical impulses in order to measure the conduction of electrical excitation and to be able to assess the functional efficiency of the corresponding nerve. The current impulses are usually delivered by electrodes glued to the skin. This is not painful.
Rarely, small needles are pricked into the skin to measure the electrical currents. In this case, pain occurs that is similar to the pain when taking blood samples. Depending on their intensity, the electrical impulses are perceived by some patients as unpleasant, but much less often as painful. Accordingly, severe pain is not to be expected during electroneurography. In the supply area of the irritated nerve, tingling or numbness may occur for a short period of time, but this quickly disappears again.
Values/Amplitude
In electroneurography, the nerve conduction velocity of the nerve under examination is determined. Since the nerves also mediate muscle function, the electrical impulses cause a muscular stimulus response, which becomes visible as a contraction. Depending on how strong the muscle contraction is, the recording of the examination shows a higher or lower stimulus amplitude.
The stronger the muscular response, the higher the amplitude. Accordingly, the amplitude is a measure of the stimulus transmission from the nerve to the muscle. If there are many functional nerve fibers in the nerve under examination, the amplitude is large.
If the nerve fibers are restricted in their function or even destroyed, this is reflected in a lower muscular stimulus amplitude. Under certain circumstances, the muscle contraction can also fail completely, so that only small or no amplitudes are shown during recording. In addition, the amplitude in electroneurography also depends on the discharge electrodes used, especially their shape and position.
The evaluation of the results of the electroneurography is done as follows: At the beginning of the examination, the stimulation electrode and the discharge electrode are applied to the skin at a certain distance. Then the electrical impulse is applied to the stimulation electrode and the time required by the nerve to conduct the impulse to the lead electrode is determined. With the help of the previously determined distance between the electrodes and the determined conduction time, the conduction speed of the nerve can now be calculated.
This varies slightly depending on the nerve, as the conduction velocity depends on various factors such as the thickness of the nerve, tissue temperature and the myelinization of the nerve (myelin surrounds the nerve as a kind of insulating layer). The measurement results are usually in the range of thousandths of a second, so that for the nerves of the arm conduction speeds of >45m/s are normal and the normal values for the lower leg nerves are >40m/s. Reduced conduction velocity can therefore provide indications of a nerve conduction disorder, which may be due, for example, to polyneuropathy as part of diabetes mellitus or other diseases such as carpal tunnel syndrome.