Cinacalcet for Management of Tertiary Hyperparathyroidism Associated with Chronic Treatment of Hypophosphatemia in an Adult with Tumor-Induced Osteomalacia

Abstract

Objective: To report the effectiveness of cinacalcet in treating tertiary hyperparathyroidism (THPT) associated with chronic treatment of hypophosphatemia in a patient with fibroblast growth factor-23 (FGF-23)-mediated tumor-induced osteomalacia (TIO). Methods: We review the clinical course, imaging studies, pathology, and results of laboratory testing of our patient and review relevant literature. Results: A 52-year-old woman presented with hypercalcemia. At age 26, she developed hypophosphatemia, inappropriately low levels of calcitriol, calcium, and intact parathyroid hormone (iPTH) and was diagnosed with vitamin D-resistant osteomalacia. She was initiated on high-dose phosphate but remained hypophosphatemic and developed progressive elevation in iPTH levels along with hypercalcemia. Twenty years after the initial presentation, a mass was found on her right forearm, and surgical resection revealed a phosphaturic mesenchymal tumor diagnostic of TIO. Her hypophosphatemia resolved and she was titrated off phosphate supplements; however, the THPT persisted. Treatment with cinacalcet resulted in lowering of calcium levels and normalization of iPTH levels. Conclusion: This may be the first reported case of managing THPT associated with chronic phosphate replacement therapy without parathyroidectomy in an adult with a FGF-23-producing tumor. Medical therapy with cinacalcet should be considered in patients with THPT associated with reversible hypophosphatemia. (AACE Clinical Case Rep. 2015;1:e225-e229) Abbreviations: 1,25(OH) 2 D = 1,25-dihydroxyvitamin D; 18F-FDG PET/CT = 18-fluorodeoxyglucose positron emission tomography/computed tomography; ADHR = autosomal dominant hypophosphatemic rickets; ARHR = autosomal recessive hypophosphatemic rickets; FGF-23 = fibroblast growth factor-23; iPTH = intact parathyroid hormone; TIO = tumor-induced osteomalacia; THPT = tertiary hyperparathyroidism; XLH = X-linked hypophosphatemic rickets