Bone Abstracts

Background: Tumor Induced osteomalacia (TIO) is a rare acquired disorder in children characterized by hypophosphatemia, phosphaturia and rickets/osteomalacia. This condition is causes by mesenchymal tumor that produce phosphaturic factors resulting in decrease renal phosphate reabsorption. Here, we report a case of FGF-23 induced hypophosphatemic rickets due to a tumor of femoral bone in an adolescent girl.

Clinical case: The proposita is now 18 years old. She was first seen at age of 12 years with gradual onset of legs pain and muscle weakness for 2 years. Physical examination revealed short stature, rachitic rosary, bowed legs, epiphyseal enlargement of both wrists, knees and ankles. Radiography of wrists and knees showed fraying of metaphyseal region, physeal widening and generalize osteopenia. Investigations revealed BUN 8.1, Cr 0.3 mg/dl, Na 137, K 3.6, Cl 105, HCO3 25 mmol/l, Ca 9.4, P 1, Mg 1.8 mg/dl, ALP 1,704 U/L, iPTH 62 pg/ml, 25-OHD 29 ng/ml, 1,25 (OHD)2 12 pg/ml and tubular reabsorption of phosphate 79%. Because she had clinical features and laboratory findings consisted with hypophosphatemic rickets which occurred later in life, TIO was suspected. The plasma FGF-23 level was assessed and the result was high (690 RU/ml). The patients underwent various radiographic investigations, including TC99m MDP bone scan, octreotide bone scan and MRI whole body, but all fail to identify the location of tumor. She was treated with calcitriol and sodium phosphate supplement. However, she developed progressive muscle weakness, bowed legs, scoliosis and multiple fractures at lower extremities. At 6 years after initial presentation, whole body 68Ga-DOTATATE positron emission tomography (PET) with non-contrast CT demonstrated an ill-defined mixed osteolytic-sclerotic lesion, about 1 cm in diameter, at lateral part of left distal femoral shaft. Wide resection of the tumor was performed. After complete resection of tumor, her serum phosphate was normalized and radiographic signs of rickets were resolved.

Conclusion: TIO is an uncommon disorder in children but should be concern in case of hypophosphatemic rickets acquired beyond infancy period. The diagnosis is challenge because tumor is difficult to find by conventional radiological methods. Surgical removal of the tumor is the essential treatment.

Disclosure: The authors declared no competing interests.