Sensory nerve conduction study in the medial antebrachial cutaneous nerve

Sensory nerve conduction in the medial antebrachial cutaneous nerve was studied in 40 normal subjects utilizing both antidromic and orthodromic methods. Using the antidromic method the distal sensory latency to the take-off point of the sensory action potential (SNAP) was 1.54 +/- 0.17 msec, latency to the peak of the SNAP was 2.11 +/- 0.16 msec, the amplitude of the SNAP was 18.8 +/- 7.1 mu v and the nerve conduction velocity was 65.9 m/sec. Using the orthodromic method the values were 1.55 +/- 0.17 msec, 2.10 +/- 0.15 msec, 15.7 +/- 6.3 mu v and 65.5 +/- 8.5 m/sec, respectively. Amplitude of the medial antebrachial cutaneous SNAP was usually smaller than that of the lateral antebrachial cutaneous nerve (p less than 0.01). This technique should be useful in the electrodiagnostic differentiation between eighth cervical or first thoracic root involvement and postganglionic lesions including the lesions of the inferior trunk or the medial cord of the brachial plexus and also in confirming involvement of this peripheral nerve due to other focal causes.