1 - Hospital Dona Estefânia – Centro Hospitalar e Universitário Lisboa Central, Department of Pediatrics
2 - Hospital Dona Estefânia – Centro Hospitalar e Universitário Lisboa Central, Adolescents Unit
3 - Hospital Dona Estefânia – Centro Hospitalar e Universitário Lisboa Central, Pediatric Nephrology Unit
- VII Congresso Hispano-Português de Nefrologia Pediátrica e XLVI Congreso Español de Nefrologia Pediátrica. 18 e 19 de Maio de 2023, NOVA Medical School, Lisboa. Poster.
Introduction: Tumor-induced osteomalacia (TIO) is a rare and frequently underdiagnosed paraneoplastic condition characterized by hypophosphatemia and inappropriately low or normal 1,25-dihydroxy vitamin D. It’s usually caused by elevated levels of fibroblast growth factor 23 (FGF23), secreted by mesenchymal tumors typically very small and difficult to locate. A high index of suspicion is required to prevent diagnostic and treatment delays.
Clinical Case: A previously healthy nine-year-old girl from São Tomé, presented with a one-year history of bilateral and symmetrical pain of the lower limbs with progressive gait impairment. She was transferred to Portugal for further investigation. She had normal stature (15th percentile) and there were no bone deformities. Lower limbs X-ray showed diffuse and symmetrical metaphyseal lucent areas and osteopenia. MRI revealed low-signal bands in all physeal plates. Laboratory workup revealed hypophosphatemia (1,7mg/dL), increased alkaline phosphate (1091U/L), with normal calcium (9,5mg/dL), PTH (72,1pg/mL) and 1,25-Vitamin D (30,50pg/mL), low tubular reabsorption of phosphate (TRP 46.9%), decreased TmP/GFR (0,94mmol/L) and increased FGF23 (284UA/mL, RR <230). Physical rehabilitation and supplementation with phosphorus and calcitriol were implemented, with progressive pain and gait improvement, but without an increase in phosphatemia. The diagnosis of TIO was considered and a PET(68Ga-DOTANOC) was performed, which didn’t identify the tumor. As TIO remained the most probable diagnosis, Burosumab was started empirically, with a progressive increase of serum phosphate (3,0mg/dL), normalization of TmP/GFR, and great improvement of physical capacity.
Conclusion: TIO is a debilitating disease characterized by a long diagnostic delay leading to metabolic disturbances and skeletal impairment. FGF23 production is usually associated with benign mesenchymal tumors however recent metanalysis revealed up to 10% of malignant histology. Although rare, TIO can occur at any age, so it should be suspected and looked at in cases where childhood inherited conditions cannot be demonstrated. Increasing awareness of TIO is crucial to decrease its diagnostic delay and clinical consequences.
Palavras Chave: Burosumab, fibroblast growth factor 23, hypophosphatemia, tumor-induced osteomalacia