Comparative study of indices of activity evaluation in rheumatoid arthritis

Choosing between the different indices of activity evaluation in RA is often difficult considering the very heterogeneous clinical expression of the disease. The objective of our study was to evaluate the level of similarity between SDAI, CDAI, DAS28-(ESR) and DAS28-(CRP) indices in the evaluation of RA activity.

In this transversal study, a total of 100 patients with RA responding to the ACR 87 criteria were followed up for a period of 20 months. The correlations between the four indices were studied through the Pearson's correlation coefficient (r). The similarity between these tools was evaluated through Kendall's (K) "tau" similarity coefficient.

The 87 female and 13 male patients (sex ratio: 6.7F/1M) were of a mean age of 52.9±11.6 years (17-77) and have been living with RA for a mean of 8.3±9 years (2 months-41 years). The DAS28-(ESR) mean score was 5.53±1.46 [1.25-8.05]. The DAS28-(CRP) mean score was 5.01±1.44 [1.68-7.81]. The CDAI mean score was 30.72±15.04 [2-62] and that of SDAI was 28.86±15.86 [2.3-71.3]. A positive, statistically significant correlation was noted between the four indices of RA activity. The level of similarity between the different indices was good (K variation between 0.758 and 0.943). DAS28-(ESR) allowed classifying the patients in the same category of disease activity than DAS28-(CRP) in a proportion of 85%. This proportion was 88% when comparing DAS28-(ESR) to CDAI and SDAI, respectively. Regarding DAS28-(CRP) and CDAI, these two indices classified the patients in the same category in a proportion of 80%, compared to 87% regarding DAS28-(CRP) and SDAI. Finally, CDAI and SDAI classified the patients in the same category in a proportion of 92% with an excellent level of similarity.

Different evaluation indices of RA activity are currently available. DAS28 is the most used. CDAI and especially SDAI have a good level of similarity with DAS28. Their advantage is to be simple and quick, and seem therefore well adapted to the follow-up of outpatients.