Category: Calcium/Bone Disorders

Monitor: 13


Saturday, Apr 27
10:30 AM – 11:00 AM

Objective : Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disorder caused by tumors that secrete fibroblast growth factor 23 (FGF23). It is characterized by decreased renal absorption of phosphate resulting in hypophosphatemia and inadequate bone mineralization. We present a case of a patient with osteoporosis (OP) and insufficiency fractures, found to have TIO secondary to sinonasal tumor.

Methods : N/A

Results : A 64-year-old woman with hypertension was referred to Endocrinology for management of OP and insufficiency fractures. One year ago, she was diagnosed with OP and started alendronate 70mg weekly. No history of alcohol, tobacco, steroid or anticonvulsant use. Eight months ago, she was involved in a motor vehicle accident complicated by non-displaced fractures in multiple ribs, vertebral bodies, and bilateral hips. Fractures were initially treated conservatively. However, due to poor healing, she underwent left femur intramedullary nail placement. Post-operative bone densitometry revealed OP in lumbar spine (T-score -2.9) and left femoral neck (T-score -3.3). Subsequent evaluation showed low calcium (8.1mg/dL, normal range [NR]: 8.7-10.5), low phosphorus (1.0mg/dL, NR: 2.5-4.5), low 24-hour urine calcium (79.55mg, NR: 100-300), low 1,25-dihydroxyvitamin D (8.2pg/mL, NR: 19.9-79.3), and high FGF23 (638 RU/mL, NR: 44-215). Vitamin D level (46.8 ng/mL, NR: 30-100) and iPTH (34 pg/mL, NR: 12-88) were within normal ranges. Due to concern for TIO, a PET scan with 68Ga-DOTATATE was performed which revealed a 4.8cm hard palate avid mass with extension into the sinonasal cavity. The patient was started on neutra-phos 250 mg QID and calcitriol 0.25 mcg BID, and alendronate was discontinued. Sinonasal mass biopsy was consistent with solitary fibrous tumor. She is scheduled for complete surgical resection.

Discussion : TIO is a rare paraneoplastic syndrome commonly caused by phosphaturic mesenchymal tumors that secrete FGF23. This hormone reduces that renal phosphate reabsorption in the proximal renal tubules and inhibits the expression of 1-alpha hydroxylase resulting in low 1,25-dihydroxyvitamin D levels. These metabolic abnormalities can be manifested by muscle weakness and pathological fractures. Once the diagnosis of TIO is confirmed, the tumor is localized by anatomical (computed tomography or magnetic resonance) or functional (PET or SPECT) imaging. Complete surgical resection can be curative.

Conclusion : Early recognition of biochemical and bone abnormalities that characterize the TIO is of utmost importance given risk for developing osteomalacia and insufficiency fractures. Localization and complete resection of the tumor can curative.


Christie G. Turin

Department of Medicine, Baylor College of Medicine
Houston, Texas

Internal Medicine Resident

Sara Bedrose

Division of Diabetes, Endocrinology and Metabolism, Baylor College of Medicine

Endocrinology Fellow

Rui Chen

Endocrinology Fellow
University of Alberta
Burnaby, British Columbia, Canada

Rui Chen a board certified internist and is currently in the 5th year of her residency training in endocrinology at the University of Alberta. She obtained her medical degree and completed her residency training in internal medicine at the University of British Columbia.

Vlad Sandulache

Assistant Professor
Otolaryngology, Head & Neck Surgery, Baylor College of Medicine

Assistant professor of Otolaryngology, Head & Neck Surgery

Reina Villareal

Associate Professor
Division of Diabetes, Endocrinology and Metabolism, Baylor College of Medicine

Associate Professor of Endocrinology

Christie G. Turin More

Internal Medicine Resident
Baylor College of Medicine
Houston, Texas

Annie Garcia