Acoustic reflex characteristics in hypo- and hyperthyroid patients

Thyroid-Stimulating Hormone and Free Thyroxine Alterations in Subjects with Occupational Hearing Loss

Context and Aim:

Occupational hearing loss (OHL) is caused by exposure to industrial noise. Alterations in the thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels are related to hearing loss. The purpose of this study is to investigate the TSH and FT4 level alterations in OHL.

Methods and Material:

Among 428 subjects, 144 male workers with normal hearing (NH), noise-induced hearing loss (NIHL), and high tone loss (HTL) (N = 48 in each group) were included in this study. All the subjects had normal TSH and FT4 levels.

Results:

The TSH level is higher in the HTL and NIHL groups in comparison to NH, but it is only significant in the HTL group. The FT4 level is significantly lower in the NIHL group; however, the lower FT4 level in the HTL group is not significant when compared to the NH group.

Discussion:

The NIHL group may turn into the HTL group over time. This process could be monitored by alteration in their TSH and FT4 levels.

Conclusions:

Alterations in the TSH and FT4 levels could be considered as a pathophysiology for OHL. More research is required to investigate the electrophysiological, physiological, and histological correlations of TSH and FT4 and different types of hearing loss caused by noise exposure.

Stapedial reflex: a biological index found to be abnormal in clinical and subclinical hypothyroidism

There is only limited evidence for biological parameter abnormalities in subclinical hypothyroidism. The aim of this study was to investigate the impact of varying degrees of thyroid failure on the stapedial reflex as a biological index, and establish its role in the evaluation of the hypothyroid patient. We studied 10 patients with subclinical hypothyroidism, 10 patients with clinical hypothyroidism, and 20 controls. All three parameters of stapedial reflex (amplitude, decay, and threshold) were measured before and after restoration of euthyroidism through thyroxine administration. Data are given as mean +/- SEM. Stapedial reflex maximal amplitudes were different among the groups studied (p < 0.0001), as values in subclinical (4.3 +/- 0.4 mm) and clinical (3.7 +/- 0.3 mm) groups before treatment were lower (p < 0.05) than those of control (5.7 +/- 0.3 mm), and subclinical (6.4 +/- 0.5 mm) and clinical (5.6 +/- 0.4 mm) groups after treatment. Similarly, stapedial reflex decays were different among the groups studied (p < 0.001), as values in subclinical (81 +/- 7 ms) and clinical (89 +/- 4 ms) groups before treatment were higher (p < 0.05) than those in control (65 +/- 2 ms), subclinical (56 +/- 8 ms), and clinical (61 +/- 8 mm) groups after treatment. There was no significant difference among the groups for stapedial reflex threshold or significant correlation between stapedial reflex parameters and thyroid function tests. Stapedial reflex, a biological parameter that reflects neuromuscular status, is abnormal in patients with subclinical and clinical hypothyroidism and returns to normal when clinical and biochemical euthyroidism has been achieved through thyroxine administration.