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.