Cochlear dysfunction evidenced by reduction of amplitude of otoacoustic responses in patients with congenital hypothyroidism

Dysfunction of the Auditory System in Children With Hypothyroidism: A Systematic Review and Meta-Analysis

OBJECTIVE

To examine the prevalence of hearing impairment in children with hypothyroidism, and to characterize clinical and subclinical hearing loss by examining cochlear function, auditory brainstem pathways, and integration of the auditory system as a whole.

DESIGN

An electronic search was conducted using PubMed, Scopus, and Cochrane Library databases. This systematic review was performed in accordance with the PRISMA guidelines. Original observational studies that utilized audiological tests for auditory system evaluations in hypothyroidism were included. A total of 2004 studies were found in the search, with 23 studies meeting the inclusion criteria.

RESULTS

The pooled prevalence of hearing loss was 16.1% [95% confidence interval 10.7, 22.4] for children with congenital hypothyroidism. Hearing thresholds at pure-tone averages (0.5-2 kHz) were 1.6 dB [95% confidence interval 1.7, 4.8] higher for children with hypothyroidism compared to age-matched controls. Cochlear dysfunction was detected at middle frequencies (1-3 kHz) by otoacoustic emission testing, indicating abnormalities of hair cell function or cochlear integration. Retrocochlear involvement was detected on auditory brainstem response (ABR), with prolonged Wave I indicating a peripheral conduction abnormality localized to the middle or inner ear and eighth cranial nerve.

CONCLUSIONS

Children with hypothyroidism have a higher prevalence of hearing loss than children without hypothyroidism. For children with congenital hypothyroidism, evidence of subclinical abnormalities at the level of the cochlea and eighth cranial nerve are present despite early initiation of levothyroxine therapy. Dysfunction of the auditory system might begin with predominance of peripheral conduction abnormalities early in development.

Low Thyroid-stimulating Hormone Levels Are Associated With Annoying Tinnitus in Adult Women: Korea National Health and Nutrition Examination Surveys

OBJECTIVE

This study aimed to investigate the relationship between thyroid function and tinnitus.

STUDY DESIGN

A cross-sectional study.

SETTING

The Korean National Health and Nutrition Examination Survey from 2013 was used.

PATIENTS AND INTERVENTIONS

A total of 1,165 participants ≥ 40 years old who were surveyed for the presence of tinnitus and underwent thyroid function tests were included. The presence of discomfort from tinnitus was defined as annoying tinnitus. The control group included participants with "no tinnitus" or "no discomfort from tinnitus." The participants were divided into the annoying tinnitus group and the control group.

MAIN OUTCOME MEASURES

The associations of free thyroxine and thyroid-stimulating hormone (TSH) with annoying tinnitus were analyzed using logistic regression with complex sampling methods. Subgroup analyses were performed according to sex.

RESULTS

The low TSH level group had 2.35-fold greater odds of annoying tinnitus than the control group (95% confidence interval  = 1.10-5.12, p = 0.027). Even in patients with a normal free thyroxine level, a low TSH level was related to 2.78-fold higher odds of annoying tinnitus (95% confidence interval  = 1.21-6.38, p = 0.016). In subgroup analyses, this association was apparent in the female subgroup. The male subgroup did not show a relationship between low TSH levels and annoying tinnitus.

CONCLUSIONS

Subclinical hyperthyroidism was related to an increased risk of annoying tinnitus. This relationship was apparent in the female subgroup.