The hearing system under thyroid hypofunction.

The auditory system has been investigated in 50 patients with thyroid hypofunction. Hearing thresholds were estimated by the pure tone audiometry, PTA. The brief tone audiometry, BTA, was carried out, evaluating differences between thresholds of shorter and longer 1-kHz tonal stimuli, 20 and 200 ms, respectively. The objective studies were established by registrations of evoked otoacoustic emissions, EOAEs, and of auditory brainstem responses, ABRs. The thresholds of ipsilateral and contralateral middle-ear muscle acoustic reflexes, ARs, were also compared. By the PTA, sensorineural hearing loss was detected in 74.0% of cases. The BTA revealed disturbances of temporal summation of excitation in cochlear receptors in 26.0% of inspected subjects. The data of the EOAE mostly corresponded to those of the PTA. In some patients, however, the PTA demonstrated normal thresholds, while the EOAEs as well as the BTA indicated abnormalities. The ABR and AR procedures detected the central hearing disorders in 30.0% and 26.0% of the tested patients, respectively. The investigations have shown that the specific hormonal therapy hardly improves either peripheral or central hearing disorders associated with hypothyroidism.