Patients and physicians often differ in their perceptions of rheumatoid arthritis (RA) disease activity, as quantified by the patient's global assessment (PGA) and by the evaluator's global assessment (EGA). The purpose of this study was to explore the extent and reasons for this discordance.
We identified variance components for the PGA and EGA in RA patients who were starting therapy with methotrexate in an academic outpatient setting. We analyzed predictors of the observed discrepancy in these measures (calculated as the PGA minus the EGA) and in their changes (calculated as the PGA(change)  minus the EGA(change) ).
We identified 646 RA patients, and among them, 77.4% of the variability in the PGA and 66.7% of the variability in the EGA were explainable. The main determinants for the PGA were pain (75.6%), function (1.3%, by Health Assessment Questionnaire), and number of swollen joints (0.5%); those for the EGA were the number of swollen joints (60.9%), pain (4.5%), function (0.6%), C-reactive protein (0.4%), and the number of tender joints (0.3%). Increased pain led to a discrepancy toward worse patient perception, while increased numbers of swollen joints led to a discrepancy toward worse evaluator perception, both explaining 65% of the discordance between the PGA and the EGA. Likewise, changes in pain scores and numbers of swollen joints proved to be the main determinants for discrepant perceptions of changes in RA disease activity, explaining 34.6% and 12.5% of the discordance, respectively.
The most significant determinants for the cross-sectional and longitudinal discrepancy between the PGA and the EGA are pain and joint swelling, respectively. Understanding the reasons for a discordant view of disease activity will help to facilitate the sharing of decision-making in the management of RA.