ODP125 Soft Bones in Crohn's: Tumor-induced osteomalacia and inflammatory bowel disease

INTRODUCTION: Bone loss is common in patients with inflammatory bowel disease (IBD) and is usually attributed to Vitamin D malabsorption, treatment with glucocorticoids or chronic inflammation. We report a case of bone loss, hypophosphatemia, and atypical fractures in a patient with IBD who was ultimately diagnosed with tumor-induced osteomalacia (TIO), a rare paraneoplastic syndrome of chronic hypophosphatemia and impaired vitamin D metabolism. CLINICAL CASE: A 39-year-old male presented for evaluation of low bone density, hypophosphatemia, and multiple stress fractures. His medical history includes Crohn's disease in biochemical remission on adalimumab and bilateral hip avascular necrosis. There was no history of significant steroid use or known family history of metabolic bone disease. He was previously highly active as a modern dancer. Over the course of 3 years, he developed progressive diffuse bony pain and he became wheelchair-bound. A whole body bone scan visualized multiple age-indeterminate atraumatic fractures, including bilateral metatarsal fractures and numerous rib fractures. Dual energy x-ray absorptiometry showed significantly low bone mass for age (Z-scores –3.4, -3.1, -3.7 at the L1-L4 spine, total right femur and right femoral neck, respectively). Physical exam was notable for a soft, subcutaneous 8 cm mass posterior to the left paraspinal muscle at the level of T12, which had previously been diagnosed as a lipoma. Laboratory evaluation revealed phosphorus 1 mg/dL (2.5-4.5 mg/dL), calcium 9.1 mg/dL (8.6-10.2 mg/dL), PTH 35 pg/mL (15-65 pg/mL), c-telopeptide 592 pg/mL (38-724 pg/mL), bone specific alkaline phosphatase 114.5 mcg/L (4-27 mcg/L), vitamin D-1,25 8.9 pg/mL (19.9-79.3 pg/mL), and vitamin D-25 34 ng/mL (normal >30 ng/mL). Fibroblast growth factor-23 (FGF-23) level was 1200 RU/mL (44-215 RU/mL), consistent with TIO. Thyroid function, dexamethasone suppression test, testosterone and IGF-1 were normal. Ga-DOTATATE PET scan demonstrated that the paraspinal soft tissue mass was strongly somatostatin avid. The patient was treated with oral calcitriol and phosphate replacement. He underwent a biopsy of the left paraspinal mass, which was consistent with a bland epithelioid and spindle cell neoplasm, most suggestive of a phosphaturic mesenchymal tumor. He is scheduled for a radical resection of the soft tissue mass. CONCLUSION: To date, there are no published case reports of TIO with coexisting IBD. Inflammatory cytokines, such as tumor necrosis factor alpha, have been shown to positively correlate with FGF-23 levels, and FGF-23 has been documented to be elevated during IBD flares. Given this, the presence of IBD may portend a worsened metabolic bone prognosis in patients who simultaneously develop FGF-23 secreting tumors. Presentation: No date and time listed