Focal mineralization defect during disodium etidronate treatment of calcinosis

The use of disodium etidronate (EHDP) for the treatment of calcinosis is complicated by the threat of drug-induced inhibition of skeletal mineralization. Adults with Paget's disease of bone treated for 6 months with 10-20 mg/kg/day of EHDP have been reported to show both a marked delay in mineralization and a diffuse excess of unmineralized bone matrix. Drug-induced bone disease is, however, a function of growth as well as of the dose and duration of therapy. Therefore, children treated with EHDP may respond differently to the drug-induced mineralization defect. A 10-year-old girl with dermatomyositis developed incapacitating ectopic calcification. After 9 months of therapy with 12 mg/kg/Day of EHDP, a small decrease in the calcinosis was accompanied by a dramatic increase in joint mobility. Bone mineral content of the radial diaphysis showed a failure to gain mineral density as expected with prepubertal growth (8 cm/year). Bone biopsy revealed a patchy excess of osteoid. Although the percentage of osteoid surface labeled by tetracycline was reduced, normal mineralization was evident in the double-labeled areas. In children, the mineralization defect occurring with EHDP treatment may be focal.