Ultrasonically Determined Thyroid Volume in Individuals with Bipolar Disorder on Lithium Prophylaxis Compared with Healthy Controls

Introduction: Lithium is a gold-standard agent for bipolar disorder (BD) and can affect the size, structure and/or function of thyroid gland with long-term exposure. Thyroid ultrasound can detect structural thyroid abnormalities, but it is under-reported with few prior studies in lithium users. The study aimed to evaluate thyroid volume and echogenicity in lithium users with BD and healthy participants, and explores its association with clinical variables and thyroid functions.

Method: This was an observational study with 102 participants in total. Study group consisted of 52 clinically-stable (HAM-D ≤ 13, YMRS <8) follow-up patients with DSM-5 BD on lithium maintenance. Healthy controls (HC) comprised 50 participants with no illness in self and family. Assessments included NIMH Life-chart, IGLSI typical/atypical scale, lithium response scale (LRS) and CGI-BP. Fasting venous sample was taken for thyroid functions, Anti-TPO antibodies and serum lithium. Thyroid ultrasonography was also conducted.

Results: Mean age of cases was 39.42 ± 12.62 years, with 42.3% females, which was comparable to HC. Median duration of illness was 10.5 years (Q1-Q3 = 6-19 years), with median lithium exposure for 4.5 years (Q1-Q3:2.2-7.75), and serum lithium 0.67 mmol/L (SD:0.31). Thyroid volume was significantly higher for cases than HC (10.67 ± 5.46 mL vs 4.30 ± 2.06 mL; p < 0.001). Relative to HC, serum TSH was higher in cases (p = 0.018), while anti-TPO positivity was comparable (14.0% vs 3.85%, p = 0.089). Thyroid nodules were more frequent in male cases (p = 0.013) compared to male controls.Thyroid volume did not show association with serum TSH (p = 0.277) and lithium response (p = 0.36).

Conclusion: Findings indicate a uniform enlargement of thyroid gland in lithium users with BD. Thyroid volume did not show association with thyroid functions and lithium response, however prospective studies may give better insight about their trajectories over time.