Waveform changes in antidromic facial nerve responses in patients with Bell's palsy.

We repeatedly tested the antidromic facial nerve response within 7 days after onset of paralysis in patients with Bell's palsy. None of 109 patients showed the triphasic waveform that reflects normal conduction of the facial nerve action potential. The waves recorded from patients showed biphasic, monophasic, or flat waveforms. Eighty-two of 88 patients with complete recovery showed biphasic waves, whereas half of the patients with nerve degeneration had monophasic or flat waves. Most patients with complete recovery maintained biphasic waves, but in patients with incomplete recovery, the waveforms changed to monophasic or flat, except in 1 case. The presence of monophasic or flat waves with a low facial score strongly suggests nerve degeneration. The antidromic facial nerve response is recommended as a method of diagnosing paralysis and monitoring the progression of intratemporal facial nerve damage during its early stages.