FRI435 A Grave Case Of Gynecomastia

Disclosure: S. Seltzer: None. A. illiams: None. T. Kader: None. Background: Gynecomastia is a common endocrinology referral. Our team saw a patient in the clinic with an unusual presentation. Clinical Case: A 28 year old male presented with worsening painful gynecomastia affecting one breast initially but eventually progressing to both breasts. His secondary concern was a 40lb weight loss and new onset tremor. He declined hypogonadal symptoms, palpitations, or new testicular growth. Exam revealed a resting pulse of 120 b.p.m., a palpable goiter, visible tremor, hyperdynamic heart sounds and bilateral tender gynecomastia. Labs revealed normal FSH, LH and hCG, high total testosterone (TT), thyroxine (T4) and triiodothyronine (T3) with positive thyroid receptor antibodies. Methimazole and beta blockade were started. He did develop an episode of atrial fibrillation requiring admission. Due to medication intolerance and patient preference the decision was made for total thyroidectomy. Three months post-surgery there was complete resolution of hyperthyroidism and gynecomastia.The differential for true gynecomastia is broad. The initial diagnostic approach includes a thorough history and physical exam followed by measuring serum testosterone (T), LH, hCG and estradiol (E2). Increased LH and low T indicates hypogonadism. Normal values may suggest an idiopathic cause. Elevated hCG warrants testicular imaging and if negative, chest and abdominal imaging to rule out extragonadal germ cell tumors. Elevated total T and LH should prompt measurement of TSH and T4 and if normal androgen resistance should be suspected. Elevated E2 and low/low normal LH should prompt testicular imaging and if normal an adrenal CT to rule out an adrenal neoplasm. If LH and T are low, prolactin should be measured as well as dedicated pituitary imaging.Any state which induces an increased E to T ratio may cause gynecomastia. The true pathophysiology in hyperthyroidism driving the increased sex hormone binding globulin (SHBG) production is unknown. It is postulated that this increase is driven by increased transcription and translation of hepatocyte nuclear factor-4ɑ secondary to elevated T4(1). SHBG more readily binds androgens than estrogens leading to a relative decrease in free T (FT). The lower FT levels result in negative feedback to the pituitary gland which causes increases in LH resulting in production of androgens, estradiol and peripheral aromatases. The increase in peripheral aromatization of testosterone leads to further elevation of the free estrogen levels. Conclusion: Hyperthyroidism should always be in the differential of gynecomastia as in our case the presentation may be atypical. References: Selva DM, Hammond GL. Thyroid hormones act indirectly to increase sex hormone-binding globulin production by liver via hepatocyte nuclear factor-4α. Journal of Molecular Endocrinology. 2009;43(1):19-27. doi:10.1677/jme-09-0025 Presentation: Friday, June 16, 2023