Facial nerve antidromic recordings in patients with Bell's palsy

Antidromic facial nerve action potentials have been recorded noninvasively from the tympanic membrane (TM) of patients with Bell's palsy. A standardized approach has been developed in normal subjects that involves differential recording between the TM and adjacent canal wall. A metal annulus on the tip of an ear speculum served as the reference electrode. The speculum was held in place by an adjustable headband. A conductive sponge electrode inserted through the speculum served as the active TM electrode. In clinical trials, nerve potentials recorded from the paralyzed side were abnormal in all patients tested, indicating that nerve pathology could be monitored with this technique. Abnormalities were evident at the first test, within the first day of paralysis for some patients, and well in advance of any abnormality in the electroneuronography (ENoG) response. There appeared to be a relationship between specific waveform abnormalities (e.g., increased peak latency, waveform temporal dispersion, decreased area) and the tendency for a patient to recover from paralysis. These observations suggest that the technique described could serve as a means for early prognosis, at a stage in which nerve damage could still be effectively treated.