Multiple Bone Cysts Caused by Hyperparathyroidism: A Case Report and Review of the Literature

Abstract

Background: Brown tumor, a skeletal complication of severe hyperparathyroidism, comprises reparative granulation tissue and proliferating fibrous tissue with hemosiderin deposition. Multiple brown tumors are extremely rare complications of primary hyperparathyroidism. Case Report: A 41-year-old woman presented with pain in the left knee. Radiography showed multiple cystic lesions in both femurs and the left proximal tibia, and additional radiography showed multiple cystic lesions in the left humerus and ulna. Magnetic resonance imaging (MRI) revealed multiple cystic lesions in the bilateral femurs, left proximal tibia, and ilium. Laboratory tests revealed hypercalcemia (albumin-corrected calcium level, 13.9 mg/dl), hypophosphatemia (phosphate level, 1.6 mg/dl), elevated level of alkaline phosphatase level (614 U/l), and markedly elevated parathyroid hormone (PTH) level (1,070 pg/ml; normal range=10-65 ng/l). 99mTc-hexakis-2-methoxyisobutyl-isonitrile scintigraphy revealed tracer accumulation in the left upper parathyroid gland, which was consistent with parathyroid tumor. Although resection of the parathyroid tumor was planned, the patient developed parathyroid apoplexy before tumor excision. After the parathyroid apoplexy, serum calcium and PTH levels temporarily normalized. Resurgence of the PTH level was observed 2 years after the diagnosis, and the patient underwent left upper parathyroidectomy. One year after the tumor excision, the patient had no symptoms, and MRI showed shrinkage of the cystic bone lesions. Conclusion: This report emphasizes the importance of considering hyperparathy-roidism as a differential diagnosis for patients with multiple bone lesions.