Acute mania after levothyroxine replacement for hypothyroid-induced heart block

Psychiatric disturbances can manifest after levothyroxine (LT4) treatment for severe hypothyroidism. We present the case of a young Filipino man with Hashimoto's thyroiditis and high-grade heart block, who was given a full replacement LT4 dose on admission. Twenty-four hours after this dose, he developed manic symptoms, which were addressed with sedatives and neuroleptics with gradual restoration of euthymia the following day. A comprehensive workup did not reveal any findings suggestive of another aetiology for either mania or heart block. We ultimately ascribed the mania as secondary to LT4, and the heart block to hypothyroidism. Although mania is more likely to be precipitated by high starting LT4 doses, reports have shown that symptoms can still arise even at lower doses and with more gradual titration, especially in long-standing hypothyroidism.