Thyroid functions in patients with bipolar disorder and the impact of quetiapine monotherapy: a retrospective, naturalistic study

OBJECTIVE: Previous studies have demonstrated a potentially close relationship between mood disorders and thyroid abnormalities. The aims of this study are to investigate: 1) whether significant differences of thyroid profiles exist between manic and depressive episodes in patients with bipolar disorder (BD); 2) the impact of quetiapine monotherapy on thyroid functions in depressed BD patients. METHODS: In this retrospective naturalistic study, we reviewed patients’ information based on an electronic medical system from January 2015 to April 2019. Patients with a discharge diagnosis of BD, a current depressive or manic episode, were screened. All depressed BD patients were treated with quetiapine monotherapy for at least one month. For all patients enrolled, the demographic, clinical data and thyroid functions were recorded. The differences between thyroid profiles including total thyroxine (TT4), total triiodothyronine (TT3), free triiodothyronine (FT3), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) between patients with different episodes were analyzed. In addition, the change of thyroid functions before and after one-month or three-month quetiapine treatment in depressed BD patients was also analyzed. RESULTS: Totally, 28 patients with a manic episode and 58 patients with a depressive episode were enrolled. No significant differences in thyroid profiles were found in patients with different mood episodes. After one-month quetiapine treatment, serum levels of TT4, FT4 and FT3 were significantly reduced (P<0.05), TSH was increased (P=0.015), while TT3 was not significantly changed (P=0.425). After three-month quetiapine treatment, serum levels of TT4, TT3, FT4 and FT3 were significantly reduced (P<0.05), except TSH (P=0.990). CONCLUSION: These findings indicate that thyroid functions were not significantly fluctuated between depressive and manic episodes in BD patients. Nonetheless, quetiapine treatment may disturb the thyroid system and needs close monitoring.