Abstract
Casestudy: Phosphaturic mesenchymal tumor (PMT) is a rare, benign neoplasm. It is associated with oncogenic osteomalacia, a paraneoplastic condition caused by secretion of a peptide hormone-like substance, fibroblast growth factor 23, which increases renal clearance of phosphate and increased mobilization of calcium and phosphate from bone. PMT is difficult to diagnose as a primary etiology because patients usually experience non- specific symptoms associated with hypophosphatemia like bone pain, muscular weakness, and pathologic fractures. Because PMT is a benign neoplasm, surgical excision is curative and rapid resolution of symptoms typically ensues. Discussed here is a case of PMT arising in the soft tissue of the medial thigh of a 65 year old man with a five year history of osteomalacia with pathologic fractures and complicated healing. Lab studies revealed hypophosphatemia, hyperphosphaturia, hypercalcemia, and elevated serum fibroblast growth factor 23 during workup for fracture. A small superficial soft tissue mass was discovered in the proximal thigh via octreotide scan which was subsequently excised. On histologic examination it was composed of an encapsulated proliferation of spindle cells in a chondromyxoid background with distinctive areas of flocculent calcification and osteoclast-like giant cells. A diagnosis of PMT was rendered. The patient’s symptoms resolved rapidly after surgery. Despite the benign characteristics and behavior of this rare neoplasm; delayed or mis-diagnosis can have severe implications for patient’s health. Interdisciplinary communication, shrewd clinical index of suspicion, and awareness of the causes of, and the tests available to diagnose oncogenic osteomalacia can speed accurate diagnosis leading to better outcomes for patients.
