Conduction studies of the medial cutaneous nerve of the forearm.

The forearm medial cutaneous nerve is a pure sensory branch from the medial cord of the brachial plexus. Its fibers are derived from the eighth cervical and first thoracic nerves. A simple, easily reproducible antidromic technique for studying conduction of the forearm medial cutaneous nerve is described with the knowledge (obtained from cadaver dissections) of its exact topography. Sixty nerves were studied in 30 able-bodied adults, 15 women and 15 men. Surface stimulation was done over the medial aspect of the middle of the arm at a level where the nerve pierces the deep fascia. Surface recordings were made 18cm distally over the course of its volar branch. Action potentials were obtained in 100% of the subjects without electronic averaging. Mean values obtained were as follows: latency to onset 2.73 +/- 0.17 msec; latency to peak 3.31 +/- 0.19 msec; conduction velocity of the fastest fibers 65.9 +/- 4.3 m/s; amplitude 15.4 +/- 4.1 microvolts, and the mean difference in latency between the right and left nerves in the same subject was 0.1 msec. Conduction studies of this nerve should be useful in electrodiagnostic evaluation of peripheral neuropathy (particularly in below amputees), local neuropathic conditions, and entrapment syndromes involving the medial cord of the brachial plexus.