Phosphaturic mesenchymal tumour in the temporal bone - A rare presentation

Background: Tumour-induced osteomalacia (TIO) is a rare clinical entity in which secondary osteomalacia is induced by tumour-related products. There is impaired reabsorption of phosphorus in the renal tubules and hypophosphatemia as a result of over expression of FGF-23 mRNA. Treatment of choice is considered to be total or near total resection of the tumour. Methods and results: A 49-year-old man had experienced systemic bone pain and bilateral limb weakness for several months. He had refractory hypophosphatemia and marked elevation of serum FGF-23 level. Magnetic resonance imaging (MRI) of the lumbar spine showed a focal lesion in the left temporal bone which was hyper metabolic on positron emission tomography (PET) scan, leading to a diagnosis of TIO. He underwent lateral skull-base surgery after thorough evaluation of the tumour. After the en bloc resection, FGF-23 became gradually undetectable, phosphate reabsorption normalised, and all symptoms were resolved. Conclusions: We present the clinical features and treatment options for this most unusual manifestation of phosphaturic mesenchymal tumour in the temporal bone.