The Little-Big Troublemaker - A Case of Oncogenic Hypophosphatemic Osteomalacia leading to irreversible renal failure and fragility bone fractures

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 199-233-Bone Biology
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-226
Gaja Andzel*1, Toni L Terry1, Shabeena Shaik1, Mahnaz Mellati1 and Elena Valerie Plummer2
1Banner Good Samaritan, Phoenix, AZ, 2Carl T Hayden VA Medical Center, Phoenix, AZ
Background: Oncogenic hypophosphatemic osteomalacia (OHO), is associated with benign, small tumors of mesenchymal origin. These tumors produce high level of fibroblast growth factor 23 (FGF –23) resulting in increased renal phosphate clearance. Timely diagnosis is critical as surgical resection is curative in most of the cases, and postponing treatment may lead to debilitating consequences including nephrocalcinosis with renal failure and severe osteomalacia with fragility bone fractures.

Clinical case: A 43 year old male was evaluated for ill-defined, painful and disabling bone disorder. Laboratory findings included serum phosphate 1.2 mg/dl (2.7-4.5), 1,25-dihydroxy vitamin D 20 pq/ml (15-60), alkaline phosphatase in high 400’s ,  normal eGFR and calcium levels. DXA scan revealed Z scores as low as -3.8 and vertebral compression fractures. Patient was diagnosed with hypophophatemic osteomalacia and supplementation with high dose phosphate and calcitriol was initiated which resulted in tremendous clinical improvement. Oncogenic osteomalacia was suspected. Diagnostic imaging failed to reveal a focal lesion.  Over following six years renal function deteriorated (eGFR 37ml/min) and patient was diagnosed with hypercalcemic nephropathy with calciphylaxis.  He eventually developed PTH-mediated hypercalcemia and had three hyperplastic parathyroid gland resected, resulting in postsurgical hypoparathyroidism with undetectable PTH.  At this time, further evaluation of his continued hypophosphatemia was pursued and FGF-23 level was found to be increased at 2115 RU/ml (ref <180 RU/ml). Octreotide scan revealed an area of increased uptake in the right toe. X-ray of the right foot revealed a nonspecific 2 x 1.1 cm structure in the region of 1st and 2nd metatarsal heads. An excision of the tumor was performed, with histological diagnosis of mesenchymal vascular neoplasm.  FGF-23 level 5 days after surgery decreased to 361 RU/ml. Shortly after tumor resection, phosphate supplementation was discontinued and phosphate levels increased above the normal range, likely reflecting hyperphosphatemia from chronic kidney disease and postsurgical hypoparathyroidism. Renal function has not improved.

Conclusion: Clinicians should have a working knowledge of OHO diagnosis and treatment options. Timely diagnosis is critical to avoid serious complications and may result in curative treatment.

Nothing to Disclose: GA, TLT, SS, MM, EVP

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