Brainstem auditory evoked potentials and cochlear microphonics in the HMSNfamily with auditory neuropathy

The aim of this work was to assess the hearing impairment in patients with hereditary motor and sensory neuropathy (HMSN). Elevation of pure tone thre sholds in the presence of preserved inner car function as suggested by coch lear microphonics (CM), absent or markedly abnormal brainstem auditory evok ed potentials (BAEP), and elevation of speech perception out of proportion to the pure tone loss were found in the patients. From 28 members of a Gyps y family, we examined two siblings aged 31 and 30 years and their nephew ag ed 20 years, all suffering from HMSN that was associated with auditory neur opathy. Al three affected members with difficulty of understanding speech h ad following investigations: pure tone and speech audiograms, BAEP, cochlea r microphonics, and nerve conduction studies (NCV). Results: the older two siblings had a flat 80 dB audiogram, whereas the younger one has flat 20 dB audiogram on the Lt. ear and 30 dB audiogram on the Rt. ear. All had no sp eech comprehension and no BAEP. Two patients had preserved cochlear microph onics on one ear. Peripheral nerves were electrically not elicitable, howev er, at the beginning of the disease nerve conduction was slow. Conclusion: in all three affected members with distinct clinical picture of HMSN their hearing impairment was proved to be due to severe auditory neuropathy in th e presence of preserved inner ear function.