The human acoustic tensor tympani reflex. A case report.

In a patient with unilateral lower motoneuron facial paralysis secondary to Bell's palsy, we evaluated the characteristics of what we believe to be an acoustically-evoked reflex contraction of the tensor tympani muscle. Ipsilateral stimulation of the involved ear yielded a pattern of impedance change different from the pattern characterizing normal stapedius muscle contraction. Threshold of the reflex was elevated, amplitude was large and variable, onset latency was greater, onset rise was more gradual, and offset decay was more rapid. Contralateral stimulation, with probe in the involved ear, failed to elicit the reflex contraction. Upon return of facial nerve function, the normal stapedius reflex contraction reappeared in response to both ipsilateral and contralateral stimulation.