Phosphaturic Mesenchymal Tumor Originating in the Orbit.

Phosphaturic mesenchymal tumors (PMTs) are rare benign neoplasms that are often associated with tumor-induced osteomalacia. We present a rare case of a PMT with primary origin in the orbit. A 53-year-old female presented with diffuse bone pain and deficiency fractures throughout the body on x-ray imaging. Antinuclear antibody, immunoglobulin G4, and parathyroid hormone were elevated at that time. An incidental apical orbital mass with medial rectus and superior oblique involvement was found on MRI of the brain. Histologic examination confirmed fibroblast growth factor 23 positivity following biopsy. At postoperative week 6, bone pain and double vision resolved. Patient chose to undergo curative treatment with external beam radiation treatment with close follow up by oculoplastic surgery, endocrinology, and radiation oncology. At postoperative month 6, the ophthalmologic examination was within normal limits and repeat MRI demonstrated significant reduction in tumor size relative to post biopsy scans. PET scan did not demonstrate further lesions systemically. The prognosis for PMTs is favorable with adequate treatment. For patients with diffuse nonspecific skeletal pain and concurrent ocular symptomatology, this rare condition should remain on the differential diagnosis.