Introduction
Polycystic ovary syndrome (PCOS) is recognized as one of the most common endocrine disorders in women, causing ovulatory and menstrual irregularity, infertility, hyperandrogenism, and metabolic dysfunction. The association of PCOS and autoimmune diseases, especially autoimmune thyroiditis, is increasingly being recognized. Graves’ disease is an autoimmune thyroiditis affecting mostly young women, and causes symptoms such as hyperthyroidism, sweating, heat intolerance, weight loss, increased appetite, and tremor.(1, 2) Characterized by lymphocytic infiltration of the thyroid parenchyma, Graves’ disease is found to be regulated by T helper 1 (Th1) lymphocytes, several cytokines, and chemokines.(3) Thyrotropin receptor autoantibodies (TRAb) act as the important indicator of the development of Graves’ disease, which is often used in clinical assessment.(4, 5) Although the exact pathogenic mechanism is not fully clear to date, an individual’s genetic predisposition, interactions between endogenous and environmental factors, and immune system dysregulation greatly contribute to the onset of Graves’ disease.(6, 7)
Previous studies showed that patients with PCOS run an elevated risk of autoimmune thyroiditis compared with those without PCOS.(8, 9) A previous clinical trial proved a positive relationship between ovary function, thyroid function, and insulin resistance in women.(10) A previous systematic review also revealed a higher prevalence of autoimmune thyroid diseases in patients with PCOS compared with those without.(11) A Danish cohort study further indicated that patients with PCOS had a higher risk to develop thyroid diseases.(12) However, only few pieces of research exclusively explored the association between PCOS and Graves’s disease. A previous case series of 6 patients indicated a positive relationship of PCOS and Graves’ disease.(13) A higher prevalence of serological indicator of Graves’ disease has also been found in PCOS patients.(14) Since the epidemiology of the relationship of PCOS and new-onset Graves’ disease hasn’t been well disclosed, we conducted this original longitudinal nationwide cohort study to explore this issue.