High prevalence of Hashimoto's thyroiditis in patients with polycystic ovary syndrome: does the imbalance between estradiol and progesterone play a role?

Objective: Some similar factors, such as genetic susceptibility and subinflammation/autoimmunity, contribute to development of both polycystic ovary syndrome (PCOS) and Hashimoto's thyroiditis (HT), suggesting a potential pathogenic link between the two common disorders. In this study, we investigated the relationship between PCOS and HT, considering the possible effect of PCOS-related hormonal and metabolic factors on thyroid autoimmunity.

Methods: Eighty-six reproductive-age women diagnosed with PCOS according to Rotterdam criteria and 60 age-BMI matched control women were included in the study. All subjects had thyroid function tests, thyroid peroxidase anti-body (anti-TPO), thyroglobulin anti-body (anti-Tg), LH, FSH, estradiol, progesterone, androgens, fasting glucose, insulin, lipid, homeostasis model assessment insulin resistance (HOMA-IR) levels, thyroid and pelvic ultrasounds.

Results: TSH, anti-TPO (p = 0.017), anti-Tg (p = 0.014), LH, DHEAS, testosterone, and HOMA-IR levels were significantly higher and progesterone were lower in PCOS women than in controls. Free T4, free T3, FSH, estradiol levels and thyroid volume were similar between the two groups. A higher percentage of PCOS patients had elevated TSH (26.7 and 5%; p = 0.001), anti-TPO (26.7 and 6.6%; p = 0.002), and anti-Tg (16.2 and 5%; p = 0.039). HT was more common in PCOS patients compared to controls (22.1 and 5%; p = 0.004). Estradiol (p = 0.003) were higher in anti-TPO positive PCOS women than anti-TPO negative ones. Anti-TPO was correlated positively with estradiol, estradiol/progesterone ratio, and TSH.

Conclusions: This study demonstrated a higher prevalence of HT, elevated TSH, anti-TPO, and anti-Tg levels in PCOS patients. Increased estrogen and estrogen/progesterone ratio seem to be directly involved in high anti-TPO levels in PCOS patients.