Vitamin D metabolism and bone histomorphometry in a patient with antacid-induced osteomalacia.

A patient with hypophosphatemic osteomalacia secondary to ingestion of large amounts of phosphate-binding antacids is presented. Vitamin D metabolites were measured during the course of his illness and recovery and demonstrated an initially elevated concentration of 1,25-dihydroxyvitamin D, an undetectable level of 24,25-dihydroxyvitamin D, and a normal level of 25-hydroxyvitamin D. These metabolites returned to normal levels when the hypophosphatemia was corrected. Bone histomorphometry showed osteomalacia with increased resorption. The possible role of altered vitamin D metabolism in the pathogenesis of this disorder is discussed.