THU450 Looking Beyond The Usual Suspects: A Rare Case Of Teriparatide Induced Gynecomastia

Disclosure: B.P. Ramchandani: None. F.S. Mirza: None. Introduction: Teriparatide (TP) is a parathyroid hormone analogue used as anabolic therapy for treatment of osteoporosis. Common side effects include nausea, headache and orthostatic hypotension. We hereby describe the first case of gynecomastia that developed shortly after starting treatment with TP, and resolved a couple of months after discontinuation of therapy. Clinical Case: A 61 year old male physician with severe osteoporosis presented to the endocrinology clinic with bilateral nipple tenderness and a firm lump under the left areolar region four months after starting therapy with TP. There was no associated bleeding or nipple discharge. He denied having any erectile dysfunction or decline in sexual function. His medications included vitamin D, lansoprazole and rosuvastatin. Family history was significant for osteoporosis and ductal carcinoma in situ in mother, and bilateral hip fractures after falls in his father at the age of 80. He denied any alcohol or recreational drug use. He was physically active but denied any recent weight loss. Other than the firm glandular tissue under left lateral areola, no other findings including nipple inversion or lymphadenopathy were noted on exam. Laboratory testing showed normal total and free testosterone level at 360 ng/dl and 68 pg/ml respectively, estradiol 39 pg/ml, LH 1.44 mIU/ml, FSH 4.44 mIU/ml, TSH 1.71 uIU/L, Prolactin 4.54 ng/ml and HCG <2 IU/ml, along with normal creatinine and liver enzymes. Mammogram showed left greater than right flame-shaped focal asymmetry contiguous with the nipple compatible with gynecomastia. Breast ultrasound showed left greater than right retroareolar dendritic slightly hypoechoic soft tissue correlating with the mammographic findings. Due to significant discomfort associated with gynecomastia, a decision was made to stop TP and treatment with risedronate was initiated. Following the discontinuation of the drug, the patient reported that his symptoms gradually improved and the nipple sensitivity and the palpable swelling of the left breast completely resolved at his follow up visit four months later. Conclusion: The temporal association between the initiation of teriparatide treatment and onset of gynecomastia, and improvement of the symptoms and physical findings upon discontinuation of the drug suggests that teriparatide was the likely cause of gynecomastia in our patient. Presentation: Thursday, June 15, 2023