Coexistence of tumor-induced osteomalacia and primary hyperparathyroidism.

OBJECTIVE: To present an unusual case of coexisting tumor-induced osteomalacia (TIO) and primary hyperparathyroidism (PHPT). METHODS: We report the clinical features, imaging studies, and the results of laboratory investigations before and after surgical resection of both a soft-tissue tumor and a parathyroid adenoma. RESULTS: A 44-year-old woman was referred to the endocrinology department with a diagnosis of PHPT accompanied by unusually severe hypophosphatemia, despite having received treatment with cinacalcet. Debilitating muscle weakness and bone pain, severe phosphaturia and hypophosphatemia, inappropriately normal calcitriol, and elevated fibroblast growth factor-23 and intact parathyroid hormone levels raised the suspicion of coexisting TIO and PHPT. Imaging studies were negative, but histologic characteristics of a palpable subcutaneous mass from the patient's thigh revealed a phosphaturic mesenchymal tumor. Complete remission after surgical removal of both the soft-tissue tumor and the parathyroid adenoma confirmed the diagnosis. CONCLUSION: The coexistence of TIO and PHPT has not been described before and can cause life-threatening hypophosphatemia. Diagnosis and localization of the tumor is of paramount importance since surgery is the treatment of choice for both TIO and PHPT.