An unusual cause of osteomalacia – A case report of phosphaturic mesenchymal tumor of the right hip bone

Abstract

Phosphaturic mesenchymal tumor(PMT), while a rare entity, is nevertheless an important cause of oncogenic
malacia/tumor‐induced osteomalacia (TIO). We present a case of PMT. Our 47‐year‐old patient presented
with unexplained osteomalacia refractory to medical therapy, associated with left subtrochanteric stress
fracture. Further workup revealed the presence of a tumor in the left anterior inferior iliac spine, which was
subsequently excised. Histopathology of the tumor showed the characteristic features of PMT, including
grungy calcifications, osteoclast‐type multinucleated giant cells, and bland round‐to‐spindled tumor cells.
Following excision of the PMT, the patient’s osteomalacia swiftly resolved. PMT is an important differential
diagnosis in the context of oncogenic osteomalacia/TIO. As highlighted by our case report, PMT has fairly
characteristic clinical and histopathologic features. However, given its rarity, an awareness of this entity is
required for correct diagnosis and treatment.