To investigate the effect of intermittent cyclical etidronate treatment on radiographic progression, bone collagen markers, and clinical disease activity in patients with rheumatoid arthritis (RA).
Forty patients with RA of less than 5 years' duration were randomized to receive intermittent cyclical etidronate therapy in conjunction with antirheumatic therapy or antirheumatic therapy alone (without etidronate) in a 2 year open-label protocol. Radiographs of hands and feet and serum samples for determination of aminoterminal propeptide (PINP), crosslinked C-telopeptide (ICTP), and aminoterminal telopeptides (NTx) of type I collagen were obtained at baseline and at 24 months.
There was significant and similar worsening of the radiologic scores in both treatment groups. Both PINP, a marker of bone formation, and ICTP, an indicator of collagen degradation, declined in the etidronate group compared to the control group (p = 0.001 and p = 0.042, respectively). The groups did not differ for the change in serum NTx, a specific systemic marker of osteoclastic bone resorption. However, the change in serum NTx correlated significantly with the increase in erosion score in the total study population and in the control group (r = 0.41, p = 0.01 and r = 0.48, p = 0.034, respectively).
Etidronate therapy did not prevent radiologic progression in patients with RA, but the decline in serum PINP and ICTP concentrations suggests a favorable effect on general bone metabolism. Correlation between the change in serum NTx and worsening of the erosion score provides biochemical evidence that osteoclast is the principal cell type responsible for focal bone resorption in RA.