Abstract
Objective
To compare the clinical utility of anti–cyclic citrullinated peptide (anti‐CCP) antibodies and rheumatoid factor (RF) testing in predicting both functional outcome and response to treatment in early inflammatory polyarthritis (IP) patients.
Methods
A total of 916 IP subjects from a primary care incidence registry (1990–1994) had anti‐CCP antibody and RF status determined at baseline. Mean change in Health Assessment Questionnaire (HAQ) score between baseline and 5 years was compared by antibody status. The effect of treatment with disease‐modifying antirheumatic drugs and/or steroids over 5 years, early (<6 months of symptom onset) versus late initiation, and duration of treatment were also compared by anti‐CCP antibody status. The analysis was adjusted for treatment decisions and censoring over the followup, using marginal structural models.
Results
Anti‐CCP antibody–positive patients (n = 268) had more severe disease both at presentation and 5 years of followup, and this was independent of RF. On adjustment, anti‐CCP antibody–negative patients treated early experienced a significant improvement in functional disability compared with anti‐CCP antibody–negative patients who were never treated (−0.31; 95% confidence interval [95% CI] −0.53, −0.08), and experienced additional benefit for each additional month of early treatment. Anti‐CCP antibody–positive patients treated early did not have a significant improvement in HAQ score compared with those not treated (−0.14; 95% CI −0.52, 0.24).
Conclusion
In this first observational study to examine the influence of anti‐CCP antibody status on treatment response, anti‐CCP antibody–positive IP patients showed less benefit from treatment, particularly early treatment, than anti‐CCP antibody–negative patients. This provides support for the inclusion of anti‐CCP antibodies as well as RF in the classification criteria for rheumatoid arthritis and for stratification by anti‐CCP antibody status in clinical trials.