Evaluation of cochleo-vestibular functions in patients with auditory neuropathy

BackgroundAuditory neuropathy (AN) is a specific hearing disorder with abnormal auditory neural responses in the presence of normal cochlear function. Affection of vestibular portion of cochleo-vestibular (VIII) nerve was only reported in few studies.ObjectivesTo evaluate the cochleo-vestibular function in these patients and to detect any relationship between both cochlear and vestibular functions.MethodThe study was conducted on forty (AN) patients. All subjects were submitted to: full audiological test battery; history taking, clinical otological examination, basic audiological evaluation, Auditory Brainstem Response (ABR), Transient Evoked Otoacoustic Emissions (TEOAEs) and threshold equalizing test (TEN). Vestibular test battery; (vestibular evoked myogenic potential (VEMP) and VNG test battery).ResultsAudiological test battery confirmed the audiological criteria for auditory neuropathy reported in the literature. Results of this work showed that, there was preservation of TEOAE in all patients. Also, there was an increase in amplitude of CM in AN. Moreover, all AN patients showed presence of dead regions that started first in low frequencies and with increase number of dead regions the mid and high frequencies also affected. In addition to that the vestibular function tests showed that VEMP was preserved bilaterally in 15 patients, unilateral in 10 patients and absent in 15 patients. On the other side, VNG showed normal central vestibular system with unilateral weakness in 10 ears only.ConclusionPatients with auditory neuropathy could also have vestibular neuropathy. Vestibular neuropathy could be classified into three groups: superior vestibular neuropathy, inferior vestibular neuropathy and superior/inferior vestibular neuropathy.