SAT-517 A Rare Case of Lithium-Induced Thyroiditis

Abstract

BACKGROUND: Lithium is known to cause both hypo- and rarely hyper- thyroidism. It inhibits release of thyroid hormone and reduces the intrathyroidal iodothyronine/iodothyrosine ratio. Due to direct toxic or immunostimulatory effect, lithium can also cause thyroiditis. Lithium-induced thyroiditis is a rare entity with an incidence rate of about 1.3 cases per 1000 person-years. Given its generally painless and transient nature, symptoms of thyrotoxicosis may erroneously be attributed to an exacerbation of mania. Clinical Case: We report the case of a 29 y/o man with bipolar disorder on lithium therapy who presented with a 2 week history of intermittent palpitations, increased irritability, racing thoughts, insomnia, tremors, increased bowel movement frequency, and 8 lbs weight loss despite an excellent appetite. He denied ocular symptoms, and did not have any recent illness, or new stressors. He had been on a stable dose of lithium for four years. The physical exam was notable for: pulse 78 bpm and regular, exophthalmos, and a palpable, non-tender, non-nodular, thyroid. Labs: TSH 0.008 uIU/ml [0.350 - 5.50], FT3 6.5 pg/ml [2.0 - 4.4], T3 2.08 ng/mL [0.6–1.94] and FT4 1.96 ng/dl [0.8 - 2.7]. TPO, TSI and anti-thyroglobulin antibodies were negative. The lithium level was in the therapeutic range. Thyroid Uptake Scan showed decreased uptake of 2.6 % [normal 10–35%]. He was started on methimazole 20mg daily and atenolol, lithium was changed to risperidone by Psychiatry. After 2 months, hyperthyroid symptoms had resolved, and he was biochemically hypothyroid (FT4 0.85 ng/dl, TSH 20uIU/ml). Methimazole and atenolol were discontinued, with sustained euthyroid state. Conclusion: Hyperthyroidism may develop after several years of lithium therapy. It may be mistaken for aggravation of mania, or for Grave’s disease, especially since lithium and Graves’ are both associated with exophthalmos. Key issues for management are whether to continue lithium and deciding if the incorporation of antithyroid medications is necessary. Of utmost importance is regular monitoring of thyroid function tests to ensure resolution of thyroiditis and to avoid the development of overt hypothyroidism.