Effect of using the Simple Erosion Narrowing Score or Sharp/van der Heijde score on power of rheumatoid arthritis clinical trials to detect differences in radiographic progression.

Objectives: The Simple Erosion Narrowing Score (SENS) is a simplification of the Sharp/van der Heijde score (SHS). Previous studies found SENS and SHS to have very similar measurement properties, but suggest that SENS has a lower discriminative ability that may result in reduced power. Therefore, we aimed to quantify the effect of using SENS rather than SHS on the power to show between-group differences in radiographic progression.

Methods: Using data from two clinical trials in rheumatoid arthritis (DRESS and BeSt), SENS was derived from the SHS. Criterion validity of the SENS in relation to the SHS was assessed by calculating the Spearman correlation. The power of both scores to show a difference between groups was compared using bootstrapping to generate 10.000 replications of each study. Then, the number of replications with a significant difference in progression (using ANCOVA adjusted for baseline scores) were compared.

Results: Correlations between SENS and SHS were all >0.9, indicating high criterion validity of SENS compared with SHS as a reference standard. There was one exception, the DRESS study showed a somewhat lower correlation for the change score at 18 months (0.787). The loss in power of SENS over SHS was limited to at most 19% (BeSt year 5). In addition, the difference in power between SENS and SHS is smaller at higher levels of power.

Conclusion: SENS appears to be a reasonable alternative to SHS, with only a limited loss of power to show between-group differences in radiographic progression.