Tumor-induced osteomalacia is a rare syndrome characterized by urinary phosphate loss with hypophosphatemic osteomalacia. The proposed pathogenetic mechanism is paraneoplastic secretion of phosphaturic factors (so-called phosphatonins).
We describe a 34-year-old male patient who presented with severe pain of the spine and ribs for at least 2 years. Bone scintigraphy using 99mTechnetium hydroxymethylene diphosphonate (99mTc HDP) showed multiple lesions suggesting metastatic disease. Bone biopsy however revealed osteomalacia. The patient had subnormal plasma phosphate levels (0.42 mmol/L; normal range, 0.87–1.45) and markedly increased phosphate clearance (82.8 mL/min; normal range, 5.4–16.2). The patient was treated with phosphate supplementation (up to 5 g daily) along with calcium (1000 mg daily) and calcitriol (1.5 μg daily). Although this therapy did not correct hypophosphatemia, it resulted in complete relief of pain within several months.
111In pentetreotide scintigraphy showed a tiny lesion of 1-cm diameter, which could be localized to the left femoral neck in close vicinity to the greater trochanter by MRI and image fusion analysis. This lesion had not been visualized by Tc-99m HDP bone scintigraphy. Intraoperatively, use of a hand-held gamma probe after administration of 111Indium pentetreotide (111In pentetreotide) clearly identified the tumor, which was completely removed and was shown to be a hemangiopericytoma. After removal of the tumor, phosphate metabolism normalized within 1 week without requirement of phosphate supplementation.
Hypophosphatemic osteomalacia, although rare, raises an important differential diagnosis. An underlying tumor may be detected only by 111In pentetreotide scintigraphy. Preoperative labeling with 111In pentetreotide is a useful tool in detecting these tumors during surgery.
This 34 year old man with osteomalacia had a small causative hemangiopericytoma detected in the 111indium pentetreotide scintography.