"Mr. A," a 61-year-old man with bipolar disorder, had been treated with lithium and haloperidol for 7 years. His thyroid function test results were normal in January 2009. Routine testing in August 2010 revealed a low therapeutic lithium level (0.50 mmol/L [normal range=0.50—1.50]) and a low thyroid-stimulating hormone (TSH) level (0.02 mU/L [0.34—5.60]). A thyroid function panel drawn 5 days later revealed low TSH (0.03 mU/L), elevated free thyroxine (1.73 ng/dL [0.58—1.64]), and elevated free triiodothyronine (4.8 pg/mL [2.4—4.2]). Results of tests for thyroid antibodies were negative. The patient was asymptomatic, and findings on a physical examination were normal. A thyroid uptake scan showed a 24-hour
131I uptake of 3.8% (normal range=7—33), normal gland size, and heterogeneous tracer activity, consistent with thyroiditis. Because of the thyroid dysfunction as well as borderline renal function (creatinine 1.3 mg/dL [0.5—1.3]), lithium was tapered off (from 600 mg/day to 300 mg/day for 7 days and then off). The patient was maintained on haloperidol monotherapy, which was titrated up. Four weeks later, the patient's free thyroxine level had normalized (0.87 ng/dL).