Phosphaturic Mesenchymal Tumor-Induced Rickets

We describe two prepubertal girls with oncogenic rickets. The first patient, 9 years of age, presented with recent-onset lower-extremity pain. The second girl, presented at 4 years of age following a 9-month period of muscle weakness, bone pain, and poor linear growth. Laboratory analyses in both patients revealed hypophosphatemia and hyperphosphaturia; elevated circulating alkaline phosphatase activity was present in one of them. Radiographic evidence of a generalized rachitic process was evident in both cases. Computerized tomography of the paranasal sinuses and facial bones in patient 1 revealed a small lesion eroding through the inner table of the left mandibular ramus. Microscopic examination of this mass revealed a spindle cell neoplasm with chondroid material, dystrophic calcification, and both osteoclast-like and fibroblast-like cells. Prominent vascularity and marked atypia were present. These features are consistent with a phosphaturic mesenchymal tumor of the mixed connective tissue variant. In the second patient, computerized tomography revealed a lytic lesion located in the right proximal tibia, with histologic features consistent with a phosphaturic mesenchymal tumor of the nonossifying fibroma-like variant. Resection of each tumor resulted in rapid correction of the phosphaturia and healing of the rachitic abnormalities. A careful search for small or occult tumors should be carried out in cases of acquired phosphaturic rickets.