The Effect of Treatment on Growth and Deformity in Hypophosphatemia Vitamin D-Resistant Rickets

Abstract

Vitamin D-resistant rickets is characterized by short stature, lower extremity deformities, and defective mineralization of bone. While basic biochemical defects vary among involved individuals, all patients show a failure of the proximal tubule of the kidney to resorb inorganic phosphate. Laboratory findings consist of low serum phosphorus, elevated alkaline phosphatase, and abnormal serum calcium. Previously recommended treatment programs of high doses of vitamin D have effected some roentgenographic improvement in the rachitic lesions, but no related increase in height or severity of deformities has been associated with significant complications resulting from vitamin D toxicity. Daily administration of low doses of vitamin D and oral phosphates has more recently been suggested to be beneficial in promoting growth and preventing deformities. Thirteen children with documented vitamin D-resistant rickets were treated with oral phosphate and low doses of vitamin D for a mean of five years, and followed for a mean of ten years. Partial roentgenographic resolution of rachitic lesions was similar to those who received vitamin D alone. While the majority had consistently lowered alkaline phosphatases, no patient had consistently normal phosphate levels. No patient exceeded the third percentile in height. One half required osteotomies of the lower extremities. All osteotomies (eight) performed before maturity required revision, whereas those done after maturity (12) did not. Since no apparent clinical roentgenographic benefit can be documented by the addition of oral phosphate to low doses of vitamin D, we would not recommend continually doing so at this time.