Oncogenic osteomalacia from nasal cavity giant cell tumor

Oncogenic osteomalacia is a rare paraneoplastic syndrome characterized by osteomalacia, which occurs as a result of excess renal phosphate excretion caused by fibroblast growth factor-23 secreted by mesenchymal tumors. This entity is rare in head and neck cancers. We report a rare case of oncogenic osteomalacia in a patient with an anterior skull base giant cell tumor.

A 34-year-old woman presented with a 5-year history of progressive weakness in both lower limbs and the trunk. Hypophosphatemia and hypocalcemia had been noted by a local physician, but her symptoms persisted despite receiving calcium and vitamin D supplements. A recent onset of epistaxis and nasal blockage led to referral to the head and neck services. Nasal endoscopy revealed a left nasal cavity mass. Further evaluation with imaging studies revealed a mass in the nasal cavity with intracranial extension. Biopsy of the lesion suggested a neurogenic tumor. A putative diagnosis of anterior skull base neurogenic tumor with paraneoplastic hypophosphatemia was made. After the biochemical parameters were corrected, the patient underwent craniofacial resection. The final histopathologic study suggested the lesion as a "giant cell tumor." During the postoperative period the patient's biochemical and clinical symptoms improved dramatically, allowing her to regain normal mobility.

Clinicians and pathologists must be aware of the clinical symptoms, laboratory abnormalities, and pathologic features of oncogenic osteomalacia, which may be caused by tumors in the head and neck and thus make an exhaustive effort to diagnose the same.