ODP448 A Case of Lithium-Induced Silent Thyroiditis

Abstract

Abstract Background Lithium is a drug used in the management of psychiatric condition such as acute mania and bipolar disorder. Lithium is generally known to decrease thyroid hormone synthesis and release, causing hypothyroidism and thyromegaly. Much less commonly, lithium can cause elevated thyroid function tests; we describe such a case. Clinical Case A 21-year-old man with bipolar disorder and polysubstance abuse, presented with acute mania and was started on Lithium. Baseline TSH was 1.42 [0.358-3.74 µIU/mL], but one week after starting Lithium, TSH was 0.1 uIU/mL [0.358 - 3.74 µIU/mL] with free T4 of 0.95 [0.76-1.46 ng/dL]. Three weeks later, TSH was 0. 01 µIU/mL [0.358 - 3.74 µIU/mL], FT4 1.52 ng/dL [0.76 - 1.46 ng/dL], FT3 6.16 pg/mL [ 2.18 - 3.98 pg/mL], total T3 221 ng/dL [76–181 ng/dL]. Six weeks after starting Lithium, TSH remained suppressed at <0. 005 µIU/mL [0.358 - 3.74 µIU/mL], FT4 1.66 ng/dL [0.76 - 1.46 ng/dL], FT3 6.21 pg/mL [ 2.18 - 3.98 pg/mL]. During this time the patient's only complaint was tremor, with no other symptoms of hyperthyroidism. Physical exam showed mild tachycardia, with no evidence of thyroid eye disease, and the thyroid gland was normal size and nontender. TSI was negative with normal thyroglobulin and iodine levels, negative thyroglobulin and peroxidase antibodies. Lithium was in the therapeutic range. Thyroid US was normal without thyromegaly, normal echogenicity and color flow and without nodules or masses. I-123 thyroid uptake and scan showed low uptake and no nodules. The patient was diagnosed with Lithium-induced silent thyroiditis. He was treated with propranolol 10 mg PO BID for tremors, which was stopped later, due to bradycardia and dizziness. Due to persistent suppression of TSH and elevated FT4 and FT3 eight weeks after initiation of Lithium, this was discontinued, and Depakote was started. Conclusion Prior studies have shown that Lithium-induced thyrotoxicosis occurs in 2.7 cases/per 1000 person-years, with Lithium-associated Graves’ disease in 1.4 cases/1000 person-years, and silent thyroiditis only in 1.3 cases/per 1000 person-years. Although rare, our case highlights the importance of considering silent thyroiditis in patients treated with lithium and hyperthyroidism.