A NEW DISEASE ACTIVITY INDEX BASED ON THE AMERICAN COLLEGE OF RHEUMATOLOGY CORE SET OF DISEASE ACTIVITY MEASURES FOR RHEUMATOID ARTHRITIS: MEAN OUTCOME INDEX FOR RHEUMATOID ARTHRITIS (MOI-RA)

Background: American College of Rheumatology (ACR) definition of improvement is a valid tool to assess treatment response in rheumatoid arthritis (RA) trials. However, various rates of ACR responses are difficult to calculate. Further, the level of current disease activity can not be defined using the ACR response criteriaObjectives: The objective of this study was to develop a continuous composite index of disease activity for RA (Mean Outcome Index for Rheumatoid Arthritis; MOI-RA) based on the seven components of ACR core set.Methods: The MOI-RA is the mean of standardized values of tender and swollen joint counts (28, 42 or 66/68); patient's self report of global disease activity, pain (visual analog scale; VAS 0-100); Health Assessment Questionnaire (HAQ), erythrocyte sedimentation rate (ESR 1-100) and doctor's global assessment of disease activity (VAS 0-100). The range of MOI-RA is 0-100, higher values mean worse outcomes. Validity of MOI-RA was evaluated in the169 early RA patients of the FIN-RACo trial. Mean change in MOI-RA from baseline to six months in patients not achieving the ACR20 response, achieving ACR20 but not ACR50, achieving ACR50 but not remission and in patients achieving remission were calculated. We also made a model where 15% of the values of the individual components of MOI-RA were missing.Results: The changes in MOI-RA are comparable and independent on the joint counts used in all ACR response classes (Fig1). The mean MOI-RA28 decreased from 38.5 to 13.3 (SRM= 1.8, ES=1.9) from baseline to 6 months, while DAS28 decreased from 5.55 to 2.77 (SRM=2.0, ES=2.8). The correlation between MOI-RA28 and DAS28 was 0.90. Minimum clinically important difference is in MOI-RA28 ≥13. Baseline MOI-RA values adjusted to sex, age, duration of symptoms and Larsen score predicted future working ability in the FIN-RACo trial patients. Despite 15% missing values of the individual components of MOI-RA, the values of MOI-RA correlated with the values calculated using complete data.Conclusion: MOI-RA is a valid index to measure disease activity and treatment response in RA.Citation: Ann Rheum Dis, volume 66, supplement II, year 2007, page 359Session: RA – other clinical aspects and comorbidity