SUN-275 Brown Tumor as a Herald of MEN1: Unveiling a Rare Diagnosis Through Bone Pains

Abstract Disclosure: H. Zahoor: None. S. Mitra: None. D. Lovre: None. S. Gupta: None. BACKGROUND: Multiple endocrine neoplasia type 1 (MEN1) is a complex, autosomal dominant genetic disorder resulting from mutations in the MEN1 tumor suppressor gene which leads to tumors in the parathyroid, pituitary, and pancreas. We report the case of a 35-year-old male who presented with skeletal complaints of bilateral hip pain secondary to Brown tumors of the pelvis, ultimately leading to the diagnosis of MEN1. CASE PRESENTATION: A 35-year-old male with a past medical history of hypertension, prolactinoma with hypogonadism (diagnosed two years earlier) and gastroesophageal reflux disease was referred to the Endocrinology clinic by Orthopedic Oncology after a Computed Tomography (CT) of the abdomen and pelvis revealed findings consistent with a Brown tumor in the superior pubic ramus. A review of medical history revealed borderline hypercalcemia over the preceding several years and two episodes of nephrolithiasis. Further evaluation demonstrated a parathyroid hormone (PTH) level of 1220 pg/mL (15-65 pg/mL), calcium 10.6 mg/dL (8.4 - 10.4 mg/dL) with albumin 4.2 g/dL (3.4 - 5.0 g/dL), and elevated 24-hour urine calcium excretion of 478.4 mg/day (100.0 - 300.0 mg/day), confirming a diagnosis of primary hyperparathyroidism (PHPT). A sestamibi parathyroid scan indicated abnormal uptake in the left parathyroid gland and a follow-up 4DCT of the neck identified three abnormal lesions consistent with parathyroid adenomas. The patient underwent subtotal parathyroidectomy, and pathology confirmed hypercellular parathyroid tissue consistent with adenoma. The patient also had a history of prolactinoma with prior pituitary Magnetic Resonance Imaging (MRI) revealing a heterogeneous mass measuring 2 x 2.7 x 2 centimeters extending into the suprasellar region and abutting the terminal internal carotid arteries. At presentation, prolactin levels were 1719 ng/mL. He responded well to medical management with cabergoline 1.125mg twice a week. Surveillance CT imaging did not show any gastrointestinal or pancreatic tumors. Genetic testing identified a mutation in the MEN1 gene, confirming the diagnosis of MEN1 syndrome. DISCUSSION: Brown tumors are benign, fibrotic, erosive bony lesions caused by excessive osteoclastic activity in severe or longstanding hyperparathyroidism, typically in pelvic girdle, ribs, or clavicles. While PHPT is common in MEN1 syndrome, severe cases leading to Brown tumors are rare. Our case presents a unique clinical course in which hip pain and discovery of a Brown tumor revealed longstanding PHPT and led to the diagnosis of MEN1 syndrome. This case highlights the importance of comprehensive patient care, where thorough chart review and identification of abnormalities in unrelated imaging, along with incorporating a known diagnosis of prolactinoma help connect the dots to a rare diagnosis of MEN1 syndrome. Presentation: Sunday, July 13, 2025