Variability of repeated facial nerve electroneurography in healthy subjects

Background: Facial electroneurography is an objective measurement of a muscle compound action potential. The amplitude ratio between the paretic and the normal side is used as a basis for estimating the prognosis of facial palsy. According to Esslen, the difference of amplitudes in healthy subjects is only 3%, Twenty healthy test persons were investigated with the aim of 1, reproducing the published data on the left-right difference in normal test subjects and 2. determining whether the amplitude ratio is constant over time after repeated measurements. Study Design: Bilateral electroneurography was conducted on 20 healthy volunteers (age range, 23-36 y; 12 men, eight women). Two investigators performed four measurements at 1-week intervals on every subject. Results: Mean amplitude ratio was 32.5%, Repeated measurements on the same individual differed considerably-from 0% to 80%. The 99% confidence interval computed from the data ranged from 26% to 39% amplitude ratio. Conclusion: The symmetry of facial evoked compound potentials postulated by Esslen and Fisch is not supported by these data. As have other investigators, the authors found significant left-right differences in healthy subjects. Furthermore, they showed for the first time that the amplitude ratio is not constant in every individual at repeated measurements. In light of these data, prognosis of facial palsy based on electroneurographic data alone seems doubtful.