Two-step technique to optimize the medial antebrachial cutaneous nerve response.

OBJECTIVE

Position of recording electrodes for the antidromic sensory-nerve conduction study (SCS) of the medial antebrachial cutaneous (MABC) nerve is conventionally determined according to the anatomical landmarks. However, the variation of its nerve course may interfere with accurate placement. In this study, we aimed to test how the systematic two-step examination, an orthodromic-antidromic series, affects the results.

METHODS

Subjects were 40 arms from 20 control subjects. For the two-step method, we first searched for the minimal threshold point over the forearm using the orthodromic technique. The recording electrode for the antidromic SCS was placed over the optimal point determined in this way.

RESULTS

The SNAP amplitude by our two-step method was 1.39 times (range 0.99-3.94) of that by the conventional method. Four out of 20 subjects showed greater than 50% (up to 83%) interside difference of the SNAP amplitude by the conventional methods, whereas the maximal interside difference was 38% by the two-step method.

CONCLUSIONS

Careful adjustment of the recording position using the two-step method would contribute to an accurate evaluation of the MABC nerve.

SIGNIFICANCE

To determine the recording position solely based on anatomical landmarks may cause erroneously abnormal interside difference for this nerve.