NERVE TESTING
In peripheral nerve injuries, accurate location and assessment of the nerve lesion is achieved through electromyography (EMG) to measure the electrical activity of muscles and nerve conduction studies (NCS) which measure electrical function of nerves in the limbs. Your clinical neurophysiologist may use either or both tests to provide accurate, quantitative information on the function of nerves and muscles. The procedure involves some discomfort from the fine needles placed into the muscles being assessed, but the results are crucial if surgery is to follow.
NCS will normally test both motor and sensory nerves, most commonly for evidence of a trapped nerve, e.g. in carpal tunnel syndrome where NCS can confirm the symptoms are not caused instead by something like a compressed disc in the neck. Testing may be pre- or intra-operatively to monitor effectiveness of surgical procedures.
The nerve is stimulated with a small, brief electrical pulse that feels like a sharp tapping sensation on the skin. When the nerve is stimulated, the extent to which the electrical signals are delayed as they pass through the muscle being tested may give an indication of how badly the nerve has been affected.
Sensory nerves can be studied using similar methods. As the compression of the nerve becomes more severe, the speed of the sensory nerve impulses becomes slower and slower and the signals become weaker until they eventually disappear altogether.