Facial electroneurography: analysis of techniques and correlation with degenerating motoneurons.

Facial electroneurography is the one electrophysiologic test that quantifies the degree of nerve degeneration. This two-part study establishes electroneurography (ENoG) as a reliable and valid system of measurement. Part I examines three different ENoG techniques in normal subjects and in patients with advanced paralysis. Myogenic compound action potential (CAP) absolute amplitudes differ according to methodology, site, and gender. Analyses of side-to-side and test-retest CAP differences demonstrate optimized and standardized recording lead techniques to be comparable and consistent when CAPs are recorded in the midface. The most significant variable is time, i.e., the inconsistency of test-retest results. The coefficient of reliability increases when averaging results of test sessions repeated at a similar point in time. Part II, an animal model, supports the correlation between ENoG predictions following facial nerve injury and the level of motoneuron degeneration, as assessed by retrograde transport of horse-radish peroxidase to the somata of the facial motor nucleus and by peripheral axon counts.