Associations Among Obstructive Sleep Apnea, Thyroid Function and Morphology Changes.

Purpose: This study unveils the complex interplay among obstructive sleep apnea (OSA), thyroid function, and morphological changes.

Methods: Data from 1,102 patients were collected retrospectively from the Department of Otorhinolaryngology-Head and Neck Surgery of the Second Affiliated Hospital of Xi'an Jiaotong University from 2012 to 2023. The patients were divided into severe and non-severe OSA groups according to their polysomnography results. The data were analyzed by sex and age stratification.

Results: Serum free triiodothyronine (FT3), total triiodothyronine (TT3), and reverse triiodothyronine (RT3) were higher in severe OSA group in the total population (p < 0.05). Similar trends were observed in male but not in female. FT3 and TT3 are higher in the severe group in the nonelderly population (age < 60) (p < 0.05), and RT3 is higher in the severe group in the elderly population (age ≥ 60) (p < 0.05). In addition, we first reveal that RT3 is associated with the diameter of the left inferior thyroid artery (L-ITA) (r=0.394, p < 0.05) and lowest transcutaneous oxygen saturation at night (lowest SpO₂) (r=-0.269, p < 0.05). The severe OSA group showed larger thyroid volume and isthmus length, as well as the thicker ITA diameter and lower left thyroid lobe resistance index (RI) (all p < 0.05).

Conclusion: Our study demonstrates a significant association between thyroid function/morphology and OSA, with distinct sex- and age-related differences. Reduced RI in severe OSA suggests its clinical utility in assessing vascular health. Increased thyroid volume and isthmus length in severe OSA may reflect ITA-related changes. These findings support our prior observations of rising thyroid hormone levels with OSA progression and highlight the need for sex- and age-stratified analyses. Integrated evaluation of thyroid function and morphology is essential for understanding OSA-thyroid pathophysiology.