8031 Pelvic Fracture Related to Brown Tumor in Severe Secondary Hyperparathyroidism

Abstract Disclosure: M. Bodenstab: None. M. Lieberman-Ulm: None. V.S. Lagari-Libhaber: None. Background: Severe hyperparathyroidism can result in end-organ damage to the skeleton, known as osteitis fibrosa cystica (OFC). Histologically, OFC manifests as “Brown tumors”, which are so named due to the hemosiderin deposition that occurs from recurring microtraumas with subsequent hemorrhage. Typical sites of presentation include the mandible, clavicle, ribs, or pelvis, but can occur anywhere in the body. Patients can present with diffuse bone pain, pathological fracture, or bone deformities, though some may be asymptomatic and diagnosed incidentally. While these tumors do not have malignant potential, they can become debilitating in their burden and mimic malignant disease. Treatment focuses on treating the underlying cause of the hyperparathyroidism. Clinical Case: A 52-year-old female with ESRD on thrice weekly hemodialysis secondary to T2DM and HTN presented with right thigh pain and difficulty bearing weight, which began one week after a mechanical fall from standing. X-ray on admission revealed acute nondisplaced pathologic fracture of the right superior pubic ramus related to an underlying 4.7 x 2.2 cm expansile osteolytic lesion. Calcium level corrected for albumin on admission was 9.3 mg/dL, phosphorous 5.6 mg/dL, and PTH 563 pg/mL. Review of our institution’s electronic medical record revealed a maximum PTH level of 1,808 pg/mL three months prior. On CT pelvis, the patient was found to have multiple osteolytic lesions also involving the sacrum, multiple vertebral bodies, and the left pubic ramus, concerning for metastatic disease. Patient underwent pelvic rami bone biopsy resulting as osteoclast type giant cells, hemosiderin deposition and fibrosis in keeping with "brown tumor" of hyperparathyroidism. The patient was started on Cinacalcet 30 mg daily, with plans to titrate as outpatient to target PTH levels. She was also instructed to continue calcium, vitamin D and calcitriol to treat the underlying condition of metabolic bone disease from CKD. Referrals were given for both orthopedic spine and orthopedic oncology for surgical evaluation of her lesions. Discussion: Osteitis fibrosa cystica has become exceedingly rare in the United States and occurs in about 2% of patients with hyperparathyroidism. Due to their low prevalence and radiologic similarity to neoplasm, “Brown tumors” may be mistaken for metastatic disease and can lead to delay in diagnosis. Histology reveals collections of osteoclasts due to excess activity intermixed with fibrous tissue and poorly mineralized woven bone, which will differentiate brown tumor from malignancy. However, further correlation with hypercalcemia and hyperparathyroidism is imperative as brown tumors and other giant cell-containing lesions may be difficult to differentiate histologically. We present this case due to its rarity in clinical practice. Presentation: 6/2/2024