Auditory investigations in hypothyroidism.

Twenty patients with thyroprivic hypothyroidism with a mean age of 34.8 years (range: 15-50 years) were investigated. Peripheral/central functions of the auditory system were assessed in the hypothyroid state and they were re-evaluated in the euthyroid state after treatment with levothyroxine. The mean observation period for re-evaluation was 3.7 months (range 3-7 months). Sixteen patients with hypothyroidism (80%) demonstrated hearing loss when compared with randomly selected age- and sex-matched normal subjects. Twelve of the hypothyroid patients had sensorineural hearing loss and 4 had mixed loss. Special hearing tests revealed a cochlear type of hearing loss. The tympanogram curve was of Type B in one ear of each of the 4 patients. Brainstem electric response audiometry showed prolonged, absolute latency of wave V and interpeak latencies I-III and I-V. The amplitudes of waves I, II and V were reduced. Following treatment with levothyroxine a statistically significant improvement in hearing thresholds was observed by pure-tone audiometry. Tympanogram curves returned to normal in 3 out of 4 patients. Brainstem electric response parameters did not show significant reversibility to normalcy following treatment. The results of auditory investigations suggest a causal relationship between hypothyroidism and hearing loss. The site of lesion in the auditory system is probably at several levels, viz. in the middle ear, and at cochlear and retrocochlear sites.