ORAL COMMUNICATION | A rare case of intracranial meningioma and tumour-induced osteomalacia

Introduction. Tumour-induced osteomalacia (TIO) is due to an overproduction of fibroblast growth factor 23 (FGF23) by mesenchymal tumours, causing hypophosphatemia, osteomalacia, and muscle weakness. TIO is cured by tumour resection, but neoplasms may be unidentifiable/ unresectable or the patient may refuse surgery.

Description. We reported the case of a 64-year-old female with multiple non-traumatic fractures, low bone mineral density, pain, and reduced independence in activities of daily living. Biochemical evaluation showed hypophosphatemia, high alkaline phosphatase/C-terminal telopeptide, slightly high parathyroid hormone and normal albumin-corrected total calcium/vitamin D. Tubular phosphate reabsorption was slow (80%), whereas FGF23 was elevated. A ⁶⁸Ga-DOTATOC PET identified a lesion in the skull, compatible with a 27×18×28 mm meningioma. Total body computed tomography and cerebral magnetic resonance confirmed the meningioma. The neurosurgeon excluded intracranial surgery/biopsy, so medical treatment with oral phosphate and calcitriol was started, resulting in improvement in pain severity/fatigue and phosphate normalization. Neither adverse events nor tumour progression occurred during follow-up.

Conclusions. Meningioma was identified as the cause of TIO, although there is limited knowledge about meningiomas causing TIO. This is the third case reported of TIO induced by an intracranial meningioma. However, an intracranial mass may hide a low-grade phosphaturic mesenchymal tumor, mixed connective tissue variant (PMTMCT).