Audiological Findings in Charcot-Marie-Tooth Disease Type 4C

Charcot-Marie-Tooth disease type 4C (CMT4C) is a hereditary demyelinating early onset neuropathy with prominent unsteadiness and occasional cranial nerve involvement. Vestibulopathy caused by the dysfunction of cranial nerve VIII has been demonstrated in a high percentage of these patients, but the presence and degree of auditory neuropathy are unknown. The aim of the study was to characterize the hearing abnormalities of a series of patients with CMT4C and to determine the presence and severity of auditory neuropathy (AN) in these patients.

Ten patients with genetically confirmed CMT4C underwent comprehensive clinical and audiological testing. The results were compared among patients in different age groups and also to the results of vestibular testing that had already been performed.

Only 3 patients had hearing problems, but 9 had hearing abnormalities on ancillary testing that were compatible with different degrees of auditory nerve dysfunction. In the mildest cases, only the abnormality of the stapedial reflex and distortion of wave I in auditory brainstem responses could be detected. In the more severe cases, tonal audiometry revealed asymmetric hearing loss. These findings were more severe in older patients, even after correcting for age-related hypoacusia. In these patients, vestibular dysfunction could also be detected and seemed to be more profound and symmetric than hearing loss.

This report confirms and defines the presence of different degrees of auditory neuropathy in all patients with CMT4C, being detectable, usually unilaterally, during infancy, and worsening with disease progression.