Tumour-induced osteomalacia: A case report of craniofacial localization

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome. It is caused by a variety of small, slow-growing mesenchymal tumors (phosphaturic mesenchymal tumour, PMT) that can produce fibroblast growth factor 23 (FGF23). FGF23, through its effect on the renal reabsorption of phosphates, causes marked phosphaturia and hypophosphatemia which, if persistent, cause bone demineralization.The vague and non-specific symptomatology (diffuse musculoskeletal pains, asthenia and frequent fractures) often makes diagnosis difficult and therefore delays treatment.Typically TIO are single tumors of mesenchymal origins which behave benignly, while the malignant histological variants are very rare. Furthermore, they favour soft tissues, and cranio-facial localization occurs in only 10–15% of cases.We report a case of TIO located in the left pterygopalatine fossa. The patient was a 68-year-old man who had been suffering from diffuse osteomuscular pain and frequent bone fractures for about two years. Biochemical testing showed elevated levels of phosphates and of 1,25 dihydroxyvitamin D, an increase in alkaline phosphatase, and hyperphosphaturia.Gallio-DOTA-octreotate somatostatin receptor positron emission tomography/computed tomography (DOTATATE PET/TC) demonstrated uptake in the left nasal sinus area. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed a left pterygopalatine fossa mass. The patient underwent surgical resection of the mass, and the histology was consistent with a mesenchymal tumour. His serum phosphate levels normalized in about 3 months after surgery, and his hip pain had resolved completely in 6–8 months. Our case highlights the importance of recognizing this disease to avoid severe disability for patients. Keywords: Tumour-induced osteomalacia, Hypophosphatemia, Fibroblast growth factor 23, Paraneoplastic disorder, Alkaline phosphatas