Hashimoto's Thyroiditis and Dry Eye Disease.

Hashimoto's thyroiditis (HT) is an autoimmune thyroid disease with characteristic lymphocytic infiltration and fibrosis. Chronic autoimmune changes that occur in the thyroid gland in HT may also affect the lacrimal gland. Objectives: This study aimed to analyze tear biomarkers and explore correlations between these biomarkers and clinical ocular parameters in patients with HT. Methods: A total of 150 participants were divided into three groups: HT (N = 50), non-HT DED (N = 50), and healthy controls (N = 50). The participants underwent a series of diagnostic tests for DED, including the Ocular Surface Disease Index, Tear Break-Up Time, Lid-Parallel Conjunctival Folds, Schirmer test without anesthetic, lissamine green and fluorescein staining. Tear samples were analyzed for cytokine and enzyme levels (interleukin 1β, tumor necrosis factor α, interleukin 6 (IL-6), interleukin 8, interleukin 10 (IL-10), interleukin 17A, matrix metalloproteinase 9 (MMP-9)) using ELISA and multiplex immunoassay. Statistical analyses were conducted to compare groups and assess biomarker correlations. Results: Dry eye disease was observed in more than half of the study group (27/50), with severe symptoms observed in 48.15% of the DED HT subgroup. IL-6 levels were significantly elevated in the DED HT subgroup compared to the non-HT DED group (p = 0.010), suggesting specificity for HT-associated DED. MMP-9 was elevated in both the HT and non-HT DED groups (p < 0.001) but lacked specificity for HT (p = 0.059). The DED HT subgroup exhibited significantly lower IL-10 levels (p = 0.008). Lissamine green staining and LIPCOF were significantly higher in the DED HT subgroup (p < 0.001). Conclusions: Dry eye disease is common in euthyroid HT patients without signs of TAO. This study highlights the potential role of IL-6. Lissamine green staining and LIPCOF are valuable diagnostic tools for assessing the ocular surface in DED HT patients.