Cochlear dysfunction in patients with acute hypothyroidism.

The effect of acute hypothyroidism on the cochlear function was studied prospectively, in a group of 52 patients with thyroid carcinoma who underwent total thyroidectomy. All patients were examined before surgery and 6-8 weeks postoperatively. During this period there was no replacement with levothyroxine and the magnitude of thyroxin depletion was monitored by serum thyroid-stimulating hormone levels. Pure-tone audiometry, tympanometry and transiently evoked otoacoustic emissions were performed. A group of healthy volunteers of similar age and sex were used as controls. Tympanograms were normal, either on initial or on repeat testing. Audiometry showed elevation of all postoperative hearing thresholds, whereas the thresholds varied significantly across frequency. Transiently evoked otoacoustic emission testing showed response signal-to-noise ratios lower in the postoperative session (hypothyroid state) than in the preoperative session on all measured frequencies. Emission levels varied significantly across frequency, with maximum response observed at 2 kHz. Comparison of significant pure-tone and otoacoustic emission shifts for individual ears showed more ears affected in otoacoustic emission testing, indicating subclinical involvement. Comparing hearing thresholds and otoacoustic emission levels between patients and controls showed significant differences on postoperative testing. It may be thus concluded that acute hypothyroidism causes elevation of hearing thresholds in humans and to a greater degree subclinical damage of the cochlear function.