The Canadian Early Arthritis Cohort (CATCH): patients with new-onset synovitis meeting the 2010 ACR/EULAR classification criteria but not the 1987 ACR classification criteria present with less severe disease activity.

OBJECTIVE: Our objective was to describe characteristics of Canadian patients with early arthritis and examine differences between those fulfilling 1987 and 2010 rheumatoid arthritis (RA) classification criteria.
METHODS: The Canadian Early Arthritis Cohort (CATCH) is a national, multicenter, observational, prospective cohort of patients with early inflammatory arthritis, receiving usual care, recruited since 2007. Inclusion criteria include age > 16 years; symptom duration 6-52 weeks; swelling of ≥ 2 joints or ≥ 1 metacarpophalangeal/proximal interphalangeal joint; and 1 of rheumatoid factor ≥ 20 IU, positive anticitrullinated protein antibodies (ACPA), morning stiffness ≥ 45 min, response to nonsteroidal antiinflammatory drug, or positive metatarsophalangeal joint squeeze test. Data from patients enrolled to March 15, 2011, were analyzed.
RESULTS: In total, 1450 patients met the eligibility criteria (1187 were followed). At baseline, mean age was 53 ± 15 years, symptom duration was 6.1 ± 3.2 months, Disease Activity Score (DAS28) was 4.9 ± 1.6, Health Assessment Questionnaire-Disability Index was 1.0 ± 0.7. Forty-one percent (n = 450) of patients had moderate (3.2 < DAS28 ≤ 5.1) and 46% (n = 505) had high (DAS28 > 5.1) disease activity; 28% of those with baseline radiographs (n = 250/908) had radiographic evidence of erosions. ACPA status was available for 70% (n = 831) of patients; 55% (n = 453) tested positive. Sixty percent (n = 718) of patients were treated with methotrexate (MTX) initially. Of 612 patients without erosions, 63% and 83% fulfilled 1987 and 2010 RA classification criteria, respectively. Seventy-three percent (n = 166) of those who did not fulfill 1987 criteria were newly identified by the 2010 criteria. These patients had less severe disease and more were MTX-naive compared to those satisfying the 1987 criteria. Forty-seven percent of all patients achieved remission at 1 year.
CONCLUSION: Patients with early RA present with moderate high disease activity; < 50% achieve remission at 1 year, despite MTX treatment in the majority. The 2010 RA classification criteria identify more patients with RA who would previously have been designated as having undifferentiated disease. However, these patients have lower disease activity at the time of identification.