Does the ENoG Value of the Orbicularis Oris Muscle Reflect All Facial Nerve Degeneration?

Objectives: 1) Compare electroneuronography (ENoG) values in patients with facial palsy using two different methods, the midline method that records compound muscle action potentials (CMAPs) from the orbicularis oris muscle (the standard muscle for facial ENoG) and five electroneurogram recordings that records five CMAPs from five different facial muscles. 2) Reveal whether the ENoG value obtained with the midline method reflects entire facial nerve degeneration. Methods: Forty patients with facial palsy were enrolled. CMAPs were recorded using the midline method, in which the anode was placed on the mental protuberance and the cathode was placed on the philtrum. Additionally, five electroneurogram recordings were obtained by placing the anode on the skin of the parietal region and five cathodes on the skin over five facial muscles (frontalis, orbicularis oculi, nasalis, orbicularis oris, and depressor anguli oris muscles). ENoG values recorded using the two methods were compared. Results: The ENoG values of the five facial muscles did not differ from those obtained using the midline method. The total ENoG value calculated by summing five CMAPs from five facial muscles, which is considered to reflect total facial nerve degeneration, was not significantly different from that using midline methods; moreover, a strong positive correlation coefficient (r = 0.87) was found between them. Conclusions: The midline ENoG method that records CMAP from the orbicularis oris muscle reflects entire facial nerve degeneration. The ENoG value calculated from the orbicularis oris muscle might be suitable to evaluate the total prognosis of facial palsy.