Optimal reference electrode placement for accessory and axillary nerve conduction studies.

BACKGROUND

Various techniques are described for proximal motor nerve conduction studies (NCSs). We investigated alternative reference electrode (E2) locations for accessory and axillary NCSs.

METHODS

Multi-channel recordings were made from trapezius or deltoid referred to different sites, and from those sites referred to a remote electrode. Responses were compared using grouped statistics, and correlation analysis.

RESULTS

For accessory NCSs, all belly:E2 montages showed comparable responses but axillary NCSs were more variable. Low amplitude contamination was seen at the sternum and contralateral acromion but greater distortion using other potential E2 sites. In both accessory and axillary studies, the ipsilateral acromion showed moderate activity, which correlated with the belly:remote response.

CONCLUSIONS

Variation in E2 electrode sites may significantly distort the measured compound muscle action potential (CMAP). For accessory and axillary NCS, a sternal reference has favorable characteristics. Other sites, such as ipsilateral acromion or deltoid insertion, may not yield a representative CMAP.