Occult nasal sinus tumours causing oncogenic osteomalacia.

Oncogenic osteomalacia (OOM) is a rare but curable cause of metabolic bone disease. We report 9 patients with OOM, including 2 patients with occult nasal sinus tumours and 1 in whom a progressive increase in the post-operative FGF23 level heralded the development of metastatic pulmonary disease. The median duration of symptoms before definitive surgical treatment was 6 years, and in one patient was more than 10 years. This series demonstrates that careful imaging of the nasal sinuses should be part of the work-up of cases of oncogenic osteomalacia, that serum FGF23 can be helpful in both diagnosis and monitoring treatment outcomes, and emphasizes that serum phosphate should be measured in patients with metabolic bone disease and/or unexplained musculoskeletal symptoms.