[Experimental study on antidromic evoked potential of the facial nerve for clinical application]

Antidromic evoked potentials (AEPs) of the facial nerve were registered from the external auditory canal (EAC) of guinea pigs to clarify the origin of AEP and to compare diagnostic values of AEP with those of conventional evoked electromyography (eEMG). 1) The latency of AEP registered from EAC was compared with those from three points along the fallopian canal. The results showed that the latency from the pyramidal portion was almost equal to that from EAC. 2) AEPs were registered from EAC following sectioning of the intratemporal portion of the facial nerve at five points between the geniculate ganglion and the stylomastoid foramen. The waveform of the AEP was biphasic when the nerve was cut proximal to the pyramidal portion. It was monophasic when sectioned peripheral to that portion. These results, together with findings from experiment 1, indicate that AEP reflects the evoked potential generated around the pyramidal portion of the facial nerve, and that AEP is useful for the topodiagnosis of facial palsy. 3) AEP and eEMG were registered to assess changes in elicitability following compression of the facial nerve. Disappearance and reappearance of the AEP reflected well the function of the facial nerve as compared to the eEMG. This also indicates that AEP is a potentially sensitive and reliable diagnostic parameter for predicting the prognosis of facial palsy. 4) Registration of AEPs was attempted in three normal human subjects and in seven patients with Bell's palsy. AEP were recordable in all three normal men. Recording was however, possible in only two of seven patients on the involved side.(ABSTRACT TRUNCATED AT 250 WORDS)