Oncogenic Osteomalacia Caused by a Phosphaturic Mesenchymal Tumor of the Oral Cavity: A Case Report

We report a case of oncogenic osteomalacia associated with a phosphaturic mesenchymal tumor in a 31-year-old woman. She was presented with severe generalized bone and muscle pain and was restricted to bed. She lost 20cm in height over the 8 years since she had first noticed a pain in her thigh. A walnut-sized, hard, soft tissue tumor was found very easily beside her lower molar teeth. Radiologic examination revealed a remarkable decrease in bone density and multiple pathologic fractures of spine, femur and phalangeal bones. Severe hypophosphatemia, hyperphosphaturia, low plasma 1,25-dihydroxyvitamin D(3) level and high plasma PTH level were disclosed at presentation. Histomorphometric examination revealed an extensive area of unmineralized osteoid and little mineralizing activity. A pharmacologic dose of 1α-hydroxyvitamin D(3) or 1,25-dihydroxyvitamin D(3) slightly increased the serum phosphate level and renal tubular reabsorption of phosphate, and slightly decreased plasma PTH level without any symptomatic improvement. Histologic examination of the tumor revealed a mixed connective tissue tumor that consisted of central woveh bones and surrounding primitive spindle cells with prominent vascularities. After removal of the tumor, all biochemical, hormonal and radiologic abnormalities disappeared with remarkable symptomatic improvement.