Audiologic findings in botulism poisoning.

Botulism poisoning results in a presynaptic failure of neuromuscular transmission, and may be expected to impair Eustachian tube and stapedius reflex function. The audiologic findings in five normal-hearing patients with type A botulism poisoning are presented. Results were varied. Two patients demonstrated type B or C tympanograms during the early stages, while three with normal middle ear function demonstrated marked bilateral or unilateral stapedius reflux threshold elevation. One patient had a reversible reflex decay, and the superimposition of a second stimulus upon the first resulted in complete recovery of reflex amplitude. A number of possible pathophysiological mechanisms are discussed.