Optimal Reference Electrode Positioning for Electroneurography at the Orbicularis Oculi: A Case Report and Short Review.

Electroneurography is one of the most useful tests for evaluating facial nerve function. Because many patients with peripheral facial palsy complain of difficulty with eye closure, recording compound muscle action potentials (CMAPs) of the orbicularis oculi (OC) is important. However, electromyographers often encounter OC CMAPs that have an initial positivity. In the present study, facial motor potentials of a healthy subject were recorded using an electrode on the acromion and electrical activities over the facial muscles were evaluated.The contralateral OC electrode was the most inactive. A CMAP recorded using two electrodes on the ipsilateral OC showed an initial positivity. It is assumed that the onset discrepancy between electrical activities of the two electrodes on the OC results in an initial positivity. Thus, the authors recommend that electromyographers avoid using a reference electrode on the ipsilateral OC for recording its CMAP. The bilateral OC montage could be useful for recording OC CMAPs.