Objective: To analyze the minimum clinically important improvement (MCII) of disease activity measures in rheumatoid arthritis (RA) using patient-derived anchors, and to assess whether criteria for improvement differ with baseline disease activity.
Methods: We used data from a Norwegian observational database comprising 1,050 patients (73% women, 65% rheumatoid factor-positive, mean duration of RA 7.7 years). At 3 months after initiation of therapy, patients indicated whether their condition had improved, had considerably improved, was unchanged, had worsened, or had considerably worsened. We used receiver operating characteristic curve analysis to determine the MCII for the Disease Activity Score based on the assessment of 28 joints (DAS28), the Simplified Disease Activity Index (SDAI), and the Clinical Disease Activity Index (CDAI), and analyzed the effects of different levels of baseline disease activity on the MCII.
Results: On average, patients started with high disease activity and improved significantly during treatment (American College of Rheumatology 20%, 50%, and 70% improvement criteria responses were 37%, 17%, and 5%, respectively). The overall mean (95% confidence interval [95% CI]) thresholds for MCII after 3 months for the DAS28, SDAI, and CDAI were 1.20 (95% CI 1.18-1.22), 10.95 (95% CI 10.69-11.20), and 10.76 (95% CI 10.49-11.04), respectively, and the mean (95% CI) thresholds for major responses were 1.82 (95% CI 1.80-1.83), 15.82 (95% CI 15.65-16.00), and 15.00 (95% CI 14.82-15.18), respectively. With increasing disease activity, much higher changes in disease activity were needed to achieve MCII according to patient judgment.
Conclusion: The perception of improvement of disease activity of patients with RA is considerably different depending on the disease activity level at which they start.