Unilateral gynecomastia as an initial presentation of hyperthyroid Graves’ disease

Summary Graves’ disease is an autoimmune condition leading to the activation of and an increase in thyroid hormone secretion. Manifestations of hyperthyroidism in Graves’ disease can vary among people. In this case, we report a 24-year-old Thai man with a rare presentation of unilateral gynecomastia along with symptoms of thyrotoxicosis. Physical examination revealed a 3 cm non-tender palpable glandular tissue beneath and around the left areola without nipple discharge and moderately diffuse thyroid enlargement with thyroid bruit. Thyroid function test showed a typical thyrotoxicosis state with elevated serum-free T4 and decreased serum TSH. His diagnosis of Graves’ disease was confirmed biochemically with a highly elevated anti-TSH receptor antibody. Early treatment with anti-thyroid medication was given first, followed by Radioiodine treatment (RAI) for definitive treatment due to high level of anti-TSH receptor antibody, enlarged thyroid and severe thyrotoxicosis presentation at a young age, which might not resolve by anti-thyroid medication alone. The patient responded well to treatment and achieved complete resolution of unilateral gynecomastia with clinically and biochemically euthyroid within 3 months after treatment. No recurrent gynecomastia was found during the 2-year follow-up. Learning points Characteristic of gynecomastia in hyperthyroidism is usually presented with bilateral progressive gynecomastia; however, unilateral gynecomastia is occasionally found as a presentation of hyperthyroidism. Complete resolution of gynecomastia without recurrence can be achieved within a few months of treatment after thyrotoxicosis is resolved in patients with hyperthyroidism with the recent development of gynecomastia. RAI for definitive treatment is recommended in young adult patients expressing very high anti-TSH antibody level with severe thyrotoxicosis.