Investigating the Validity of the Minimal Disease Activity State for Patients with Rheumatoid Arthritis Treated with Abatacept

Objective. To validate the definitions of minimal disease activity (MDA) in patients with rheumatoid arthritis (RA) and to compare abatacept to control with respect to patients attaining a state of MDA. Methods. Two randomized controlled trials comparing abatacept to control in patients with RA were considered: ATTAIN and AIM. Core set measures, Disease Activity Score 28-joint count (DAS28), and, for AIM, radiographic scores were available. The core set and DAS-based definitions for MDA were calculated and the number of patients in the treatment groups meeting the definitions was compared to determine sensitivity of the criteria to treatment differences and patient severity. The number of times achieving MDA was compared to the change in Health Assessment Questionnaire (HAQ), and for the AIM study compared to change in radiographic scores. Results. For both definitions of MDA, the change in radiographic scores showed a continual decrease in progression the more often a patient was in MDA. The change in HAQ, for both studies, showed a similar consistent improvement - the longer a patient was in MDA, then the better the HAQ score. Significantly more patients in the abatacept group met the core set and DAS-based definition of MDA than in the control group. Conclusion. The presence and persistence of MDA was associated with slowing of radiographic progression and improvement in the HAQ, providing support for discriminative and predictive validity of the measure. The MDA results were consistent with other efficacy analyses indicating a treatment advantage for abatacept. (First Release Jan 15 2009; J Rheumatol 2009;36:260-5; doi: 10.3899/jrheum.080059)