Bilateral cochlear implantation in Friedreich's ataxia: a case study

With an incidence of 1:29 000 among Caucasians, Friedreich's ataxia (FRDA) is the most common inherited ataxia, leading to both sensory and motor degeneration. Despite many FRDA patients exhibiting normal or near normal sound detection thresholds, many individuals show abnormal neural conduction along their central auditory pathways. Electrophysiological testing can show abnormal or absent cochlear nerve and auditory brainstem recordings in the presence of normal pre-neural cochlear function (otoacoustic emissions or cochlear microphonics). This pattern of normal pre-neural cochlear function and disrupted neural conduction has been termed auditory neuropathy spectrum disorder (ANSD). Studies of FRDA patients with ANSD have shown that they exhibit severe deficits in temporal processing, impaired frequency discrimination, and deficits in speech perception. Rehabilitation of these auditory percept deficits remains difficult, as hearing aids may amplify sounds without adding clarity to the temporally disrupted or distorted signal that FRDA patients with ANSD may receive. There is limited data on the best intervention for patients with FRDA with ANSD, although personal radio aids (FM systems) have been shown to be beneficial. We report a case, where cochlear implantation has led to a dramatic improvement in speech perception in an individual with FRDA and ANSD. The majority of the literature on ANSD treatment has focused on paediatric patients with the 'dyssynchrony' type of ANSD, rather than the true neuropathy type underlying the hearing loss in FRDA patients.