Phosphorus-Calcium and Bone Metabolism in Children with Dystrophic Epidermolysis Bullosa: Cross-Sectional Study

Background. Dystrophic epidermolysis bullosa (EB) is a rare skin disease, and secondary osteoporosis is one of its complications. The bone remodeling condition in this pathology has not been studied enough. Objective. The aim of the study is to study the characteristics of phosphorus-calcium and bone metabolism in children with dystrophic EB.

Methods. The study included children with dystrophic EB aged from 3 to 18 years undergoing inpatient treatment. The ratio of children with phosphorus-calcium metabolism disorders was determined: reduced concentration of total calcium < 2.2 mmol/l, and phosphorus < 1.25 mmol/l. Additionally, deviations from reference values for 25(OH)D, parathormone, osteocalcin, C-terminal telopeptide of type 1 collagen (CTX-I) concentrations and alkaline phosphatase activity were established.

Results. Hypocalcemia was revealed in 16 patients (41%) and hypophosphatemia — in 3 (8%) patients out of 39 children with EB (22 girls, median age 77 (46; 136) months). Vitamin D level was lower than optimal (< 30 ng/ml) in 20 (77%) children with EB, while lower osteocalcin concentration — in 26 (67%), and lower CTX-I concentration — in all patients. At the same time, the median CTX-I concentration (1.32 ng/ml) more than doubled the upper values of the reference range for this indicator (< 0.573 and < 0.584 ng/ml for girls and boys, respectively). The low parathormone concentration was revealed in 1 (3%) patient. The alkaline phosphatase activity was within the reference range in all cases.

Conclusion. Disorders of phosphoruscalcium (mainly calcium) metabolism are present in large number of children with dystrophic EB. Therewith, most patients have shown vitamin D deficiency, as well as signs of bone resorption dominance (high CTX-I concentration) over bone development (low osteocalcin concentration). In general, all revealed changes in the biochemical indicators of bone remodeling indicate the development of secondary osteoporosis in most children with EB.

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