An antidromic study of the medial antebrachial cutaneous nerve, with a comparison of the differences between medial and lateral antebrachial cutaneous nerve latencies.

Electrodiagnostic study of the medial antebrachial cutaneous (MAC) and lateral antebrachial cutaneous (LAC) nerves is not routinely undertaken. Pathology of either nerve or of the brachial plexus may occur from a variety of causes. Iatrogenic injury of these nerves has been rarely reported, but potential exists for nerve damage with a number of medical procedures, implants, or surgeries in the flexor forearm. In any of these situations, nerve conduction studies on the MAC and the LAC can be of benefit. Previous studies have reported normal values and examined side- to-side differences in the LAC, but have not compared the latencies of the MAC to the LAC in the same limb. This study establishes normal nerve conduction study values for the MAC from 207 subjects with no risk factors for neuropathy, using a 10-cm distance and an antidromic technique. It also examines both side-to-side differences in the MAC and same-limb differences between the MAC and LAC. For this study, the upper limit of normal (ULN) was defined as the 97th percentile of observed values. The lower limit of normal (LLN) was defined as the 3rd percentile of observed values. The onset latency, peak latency, onset-to-peak amplitude, peak-to-peak amplitude, rise time, and duration were recorded. For the MAC, the mean onset latency was 1.7 +/- 0.2 ms, with a ULN of 2.0 ms. Mean peak latency was 2.2 +/- 0.2 ms, with a ULN of 2.6 ms. Onset-to-peak amplitude was 13 +/- 7 muV, with a LLN of 4 muV. Peak-to-peak amplitude was 10 +/- 7 muV, with a LLN of 3 muV. Side-to-side differences in MAC onset and peak latencies were 0.0 +/- 0.2 ms, with a ULN of 0.3 ms. Up to a 67% side-to-side decrease in MAC onset-to-peak amplitude was within the normal range. A 78% side- to-side decrease in MAC peak-to-peak amplitude was within the normal range. For the same-limb comparison of the MAC and the LAC, both onset and peak latencies had a mean difference of 0.0 +/- 0.2 ms and a ULN of 0.3 ms, regardless of whether the MAC or the LAC had the longer latency.