Limited availability of nutritional vitamin D causing inappropriate treatment of vitamin D deficiency rickets with a response resembling pseudohypoparathyroidism Type II in a Japanese patient

Abstract

Vitamin D deficiency rickets occasionally resembles pseudohypoparathyroidism type II (PHP type II) with respect to the response to exogenous PTH in the presence of hypocalcemia. We encountered a Japanese patient with stage 2 vitamin D deficiency rickets, who had increased urinary cAMP excretion and no response of urinary phosphate or N-acetyl-β-D-glucosaminidase excretion to exogenous PTH under normocalcemic and normophosphatemic conditions, after treatment with 1,25(OH)₂ vitamin D₃. This case shows that it is possible for a response mimicking that of PHP type II to occur when the serum calcidiol level is low due to causes other than hypocalcemia and secondary hyperparathyroidism. When the serum calcidiol level is low, the appropriate treatment should be cholecalciferol or ergocalciferol. However, because neither is commercially available as a useful formulation in Japan, physicians are forced to inappropriately use calcitriol or analogs.