Brief report: the cochlear microphonic as an indication of outer hair cell function.

The extra-cellular cochlear microphonic is believed to be generated predominantly by outer hair cells and therefore it would seem reasonable to assume that the presence of a cochlear microphonic excludes outer hair cell dysfunction. Indeed, a diagnosis of auditory neuropathy might be, and has been, made on the basis of a cochlear microphonic present with an abnormal auditory brainstem response. Animal studies, however, have shown that the cochlear microphonic recorded from the round window is dominated by cellular generators located in the base of the cochlea. Primarily on this basis, it is argued that the presence of a cochlear microphonic does not exclude outer hair cell pathology and so outer hair cell integrity should not necessarily be inferred from the presence of the cochlear microphonic alone. In contrast, the absence of an otoacoustic emission in such cases is consistent with outer hair cell dysfunction.