Successful Treatment of Tumor-Induced Osteomalacia due to an Intracranial Tumor by Fractionated Stereotactic Radiation Therapy

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 199-237-Disorders of Parathyroid Hormone & Calcium Homeostasis
Translational
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-208
Valentina D. Tarasova*1, Alejandro Trepp2, Robert Thompson3, Robert R Recker4, William Chong5, Michael T Collins6 and Laura A Armas4
1Creighton University, Omaha, NE, 2Creighton University, 3University of Nebraska Medical Center, 4Creighton Univ, Omaha, NE, 5Food and Drug Administration, Silver Spring, MD, 6National Institute of Health, Bethesda, MD
Introduction: Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome,  characterized by tumor secretion of fibroblast growth factor-23 (FGF23) causing hypophosphatemia due to renal phosphate wasting and inappropriately normal or low 1,25-(OH)2vitamin D. It is treated with phosphorus and calcitriol supplementation, and definitively by surgery.

Clinical Case: A 67-year-old female presented with multiple non-traumatic fractures, as well as progressive bone pain and muscle weakness over 4 years. She had bilateral femoral neck, pubic rami, clavicle, multiple rib and sacral insufficiency fractures, as well as marked thoracic kyphosis due to vertebral compression fractures. She had a history of what was thought to be severe osteoporosis, HTN and anxiety. Laboratory workup included serum levels of phosphorus 1.8 mg/dL (2.5-4.9), calcium 8.7 mg/dL (8.5-10.5), 1, 25-(OH)2vitamin D 36 pg/mL (15-60), 25-OH vitamin D 30 ng/dL (20-100) and PTH 87 pg/mL (11-67). Renal phosphate wasting was confirmed by high fractional excretion of phosphorus of 28% (<5%). The plasma FGF23 level of 132 pg/ml (10-50) established FGF23-dependent phosphate wasting disorder consistent with TIO, since there was no family history of hypophosphatemic disorders, rickets or short stature, and there was no history of exposure to tubulotoxic agents.

The tumor localization assessment included CT scans, MRIs, octreoscan, fluorodeoxyglucose PET/CT scan and tumor sestamibi scan. A known 1.6 cm left frontal mass, previously presumed to be a meningioma was thought to be the cause of TIO. She had a selective venous sampling at NIH that revealed a clear step up in the FGF23 level as the meningioma was approached anatomically. The patient was offered a surgical removal of the mass via craniotomy; however, she declined because of the potential risks of complications. Instead she underwent fractionated stereotactic radiotherapy for 6 weeks in 2009.

She was treated with oral phosphate (initially 2g or 8 tabs/day of K-Phos Neutral), calcitriol (1 mcg/day), calcium (1600 mg/day) and vitamin D (800 IU/day). By 3.5 years after radiation therapy she had a slow decrease in oral phosphorus and calcitriol requirements, to 1 pill of phosphorus/day and 0.5 mcg of calcitriol/day. Tumor size remained stable. Further, she has not had any fractures and her bone density has increased by nearly 50%.

Conclusions: TIO is usually caused by very small benign mesenchymal tumors that at times are hard to localize, and surgery with wide excision of the tumor borders can be associated with considerable morbidity, depending on the location. Fractionated stereotactic radiotherapy was an effective treatment modality for TIO in our patient. We propose considering fractionated stereotactic radiation therapy in addition to medical treatment, as an alternative to surgery for patients with TIO who are not surgical candidates or who refuse surgery.

Nothing to Disclose: VDT, AT, RT, RRR, WC, MTC, LAA

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm