Investigation of the Effects of Hypothyroidism Duration on Hearing Function: An Experimental Animal Study

Congenital hypothyroidism is well known to impair auditory development and function. However, the effect of acquired hypothyroidism, particularly regarding its duration, has not been clearly defined. Data investigating the relationship between prolonged hypothyroidism and hearing remain scarce. This experimental study aimed to evaluate the impact of different durations of hypothyroidism on hearing function and cochlear morphology in Wistar albino rats.

Four groups were established, each consisting of at least 8 Wistar albino rats. The groups included a control group and 3 hypothyroid groups exposed to 6-n-propyl-2-thiouracil (PTU) for 15, 30, and 45 days, respectively. PTU was administered intraperitoneally on a daily basis. Auditory evaluation was performed using otoacoustic emission (OAE) and auditory brainstem response (ABR) testing before and after the experimental period. Biochemical confirmation of hypothyroidism was obtained through measurement of serum T4 and TSH levels, collected from intracardiac blood samples prior to sacrifice. Additionally, cochlear tissue was examined histopathologically to assess possible structural alterations.

ABR analysis revealed that the 15-, 30-, and 45-day hypothyroid groups exhibited increased auditory thresholds and prolonged wave latencies compared with baseline values (P < .05). Intergroup comparisons demonstrated significant differences in latency values across all groups (P < .05). OAE responses also showed reduced amplitudes in hypothyroid animals. Histopathological evaluation indicated marked structural changes in the cochlea in all hypothyroid groups when compared to controls (P < .05), consistent with the electrophysiological findings.

Experimentally induced hypothyroidism adversely affects auditory function in a duration-dependent manner. The condition was found to impair both ABR and OAE outcomes, accompanied by histopathological changes in cochlear tissue. These findings confirm that thyroid hormones play a crucial role in preserving auditory physiology, and prolonged hypothyroidism may progressively disrupt hearing at both functional and structural levels.