Contribution of progression of erosive damage in previously eroded joints in early rheumatoid arthritis trials: COBRA trial as an example

Objective. In rheumatoid arthritis (RA) in the context of a drug trial, prevention of erosions in undamaged joints is often considered more important than prevention of progression in already damaged joints, although a clear rationale is lacking. The aim of this study is to evaluate the relative contribution of separate components of the erosion score of the modified Sharp/van der Heijde method in early RA. Methods. Different aspects of erosive damage were evaluated by their ability to discriminate between the 2 treatments in an early RA trial (the COBRA trial). Results. The contribution of progression of already eroded joints to the total erosion score clearly increased during the 1.5 years of the trial. When the periods 0-28, 28-56, and 56-80 weeks were analyzed separately, the erosion score showed a significant difference between the groups in the first 2 periods (P < 0.0001, P < 0.03, and P < 0.64, respectively). Similar differences were seen in rates of progression in previously eroded joints (P = 0.005, P = 0.003, P = 0.35). On the other hand, rates of progression in newly eroded joints showed no significant difference between the 2 treatment groups in the second and third period (P < 0.0001, P < 0.16, P < 0.87). Analyses on joint and patient level showed analogous results. Conclusion. Subanalyses on progression rates in noneroded joints and already eroded joints can provide additional information. However, important information and discriminative strength may be lost when assessment is limited to the development of erosions in undamaged joints.