CALCIUM TRACER KINETICS SHOW DECREASED IRREVERSIBLE FLOW TO BONE IN GLUCOCORTICOID-TREATED PATIENTS

Osteopenia resulting from pharmacologic doses of glucocorticoids is we ll known. Previously, there has been no satisfactory quantitative mode l describing the kinetics of calcium flow in subjects on chronic stero id use. A mathematical model of calcium isotope interaction with bone is described and applied to determine an estimate of kinetic parameter s characterizing these changes. Calcium tracer dilution kinetics after a bolus injection of Ca-42 were measured in 14 subjects with juvenile dermatomyositis, 6 on prednisone regimens and 8 on treatment regimens without prednisone. Irreversible tracer loss from plasma bone is foun d to be significantly reduced (P = 0.043) in the glucocorticoid-treate d patients compared with patients on nonsteroid regimens. Reversible f low to bone is noted to be similar in the two groups. These results su ggest a direct effect of glucocorticoids on osteoblast function.