Brown tumors of hyperparathyroidism misdiagnosed as multifocal Giant Cell Tumors of bone: A case report

Introduction: Hyperparathyroidism is a condition caused by hyperactivity of parathyroid glands. It can cause a lytic bone lesion which similar to a Giant Cell Tumor (GCT) and is hard to differ from it. The common terms for these tumor-like bone lesions are osteitis fibrosa cystica or brown tumor and they represent the end stage of bone remodeling process in prolonged hyperparathyroidism. Case presentation: A 53-year-old female complained about pain around her right shoulder. Radiographic appearance showed that there are multiple lytic lesions on right proximal humerus and some other bones. Histopathology revealed that it was most consistent to GCT of the bone. Patient underwent tumor resection surgery and shoulder hemiarthroplasty. Post-operative evaluation showed that there was an increased level of serum calcium and ionized calcium, but decreased level of phosphate. Parathyroid hormone level was high. Patient was suggested to undergo further thorough examination for the underlying cause of hyperparathyroidism. But unfortunately, a couple months after surgery, patient passed away. Discussion: Based on the history, clinical, laboratory, and radiograph findings, we thought about multiple myeloma or metastatic bone disease at first. After histopathology report said that it was most consistent to GCT of the bone. We thought about multifocal GCT of the bone then. Since the incidence of multifocal GCT was considered very rare, the lesions were multiple, and the clinical condition was not suitable for GCT, we thought about possibility of metabolic condition. Further laboratory examination of serum calcium and phosphate turned out to be hypercalcemia and hypophosphatemia. Thus we thought about brown tumor of hyperparathyroidism. Parathyroid hormone level was checked later and turned out to be high. Conclusion: Brown tumor of hyperparathyroidism should be considered when we found a case of multifocal osteolytic bone lesions. Normally, we would thought about multiple myeloma or metastatic bone disease at first. But when the laboratory, radiographic and histopathological examination results did not correlate to those diagnosis, we should order serum calcium, phosphate and parathyroid hormone level evaluation for patients with multiple osteolytic lesions. Any misdiagnosis and further harmful mistreatment for patients should be avoided.