Primary Hyperparathyroidism With Brown Tumor-A Case Mistaken as Non-Ossifying Fibroma Resolved by Biochemical and Radiological Correlation.

Primary hyperparathyroidism (PHPT) is uncommon in the pediatric population and rarely presents with overt skeletal complications such as brown tumors. This case study describes a 16-year-old female who initially presented with abdominal pain and was subsequently found to have severe hypercalcemia (serum calcium 16.4 mg/dL) and markedly elevated parathyroid hormone (PTH 1700 pg/mL) and bilateral nephrolithiasis. There were no features suggestive of multiple endocrine neoplasias. A history of a previously diagnosed "non-ossifying fibroma" in the proximal tibia was later reinterpreted as a brown tumor following the diagnosis of PHPT. Imaging studies revealed widespread bone tumors with multiple lytic lesions in long bones and the axial skeleton. Localization with a sestamibi scan confirmed a left inferior parathyroid adenoma, which was surgically resected and biopsy confirmed the same. Postoperatively, serum calcium normalized, and radiographs at follow-up showed progressive healing of bone lesions. This case underscores the importance of biochemical and radiological findings for the appropriate diagnosis of PHPT, facilitating definitive surgical management and improved clinical outcomes. This case also illustrates the reversibility of skeletal changes following curative parathyroidectomy.