Burosumab, a Transformational Treatment in a Pediatric Patient With Cutaneous-Skeletal Hypophosphatemia Syndrome

Cutaneous-skeletal hypophosphatemia syndrome (CSHS) is a rare disorder characterized by the presence of melanocytic nevi, dysplastic cortical bony lesions, and fibroblast growth factor 23 (FGF23)-mediated hypophosphatemic rickets. Herein, we describe the diagnosis of an 8-year-old girl presenting with short stature, reduced lower limb mobility, and abnormal gait due to muscle weakness and constant pain in the legs. Biochemical parameters demonstrated hypophosphatemia, hyperphosphaturia, slight increase in parathyroid hormone (PTH), high levels of alkaline phosphatase, and elevated FGF23. Burosumab improved phosphate-wasting, serum phosphorus, alkaline phosphatase, and PTH, followed by a significant mineralization in vertebral bodies evidenced by radiographic assessment. Our report shows a long-term follow-up of CSHS with a notable improvement promoted by an anti-FGF23 therapy.