Association between lithium use and thyrotoxicosis caused by silent thyroiditis

OBJECTIVE: To determine the incidence of silent thyroiditis in lithium users and characterize lithium-associated thyrotoxicosis. DESIGN: Retrospective record review. PATIENTS: 400 consecutive patients (300 with Graves' disease and 100 with silent thyroiditis) who underwent radioiodine scanning of the thyroid. MEASUREMENTS: Odds of lithium exposure. RESULTS: The odds of lithium exposure were increased 4.7-fold in patients with silent thyroiditis compared with those with Graves' disease (95% CI: 1.3, 17). Lithium-associated silent thyroiditis occurred with an incidence rate of approximately 1.3 cases per 1000 person-years, and lithium-associated thyrotoxicosis occurred with an incidence rate of approximately 2.7 cases per 1000 person-years, higher than the reported incidence rates of silent thyroiditis (< 0.03-0.28 cases per 1000 person-years) and of thyrotoxicosis (0.8-1.2 cases per 1000 person-years) in the general population. CONCLUSION: Thyrotoxicosis caused by silent thyroiditis might be associated with lithium use.