Baseline characteristics of patients with inflammatory polyarthritis included in the analysis, stratified by cohort
| Cohort 1 (1990–1994) | Cohort 2 (2000–2004) | Median difference/OR/ relative difference (95% CI)* | |||
| N | Median (IQR) | N | Median (IQR) | ||
| Age at symptom onset (years) | 1022 | 54 (41–67) | 631 | 58 (47–70) | 4.00 (2.00 to 6.00) |
| Gender (n (%) female) | 662 (64.8) | 408 (64.7) | OR 0.99 (0.81 to 1.22) | ||
| Smoking status | 1021 | 569 | |||
| Never, n (%) | 323 (31.6) | 181 (31.8) | |||
| Ex-smoker, n (%) | 424 (41.5) | 245 (43.1) | RRR 1.03 (0.81 to 1.31) | ||
| Current smoker, n (%) | 274 (26.8) | 143 (25.1) | RRR 0.93 (0.71 to 1.22)† | ||
| Symptom duration (months) | 1022 | 5.1 (2.7–9.4) | 631 | 6.6 (3.9–11.3) | 1.54 (0.89 to 2.18) |
| Swollen joint counts | |||||
| 28 | 1022 | 5 (1–11) | 631 | 2 (0–6) | − 39% (−45% to −31%) |
| 51 | 1022 | 6 (2–13) | 631 | 3 (1–8) | − 40% (−46% to −33%) |
| Tender joints counts | |||||
| 28 | 1022 | 5 (2–12) | 631 | 2 (0–8) | −29% (−37% to −20%) |
| 51 | 1022 | 7 (3–16) | 631 | 4 (1–12) | − 25% (−33% to −16%) |
| CRP (mg/L) | 817 | 5 (0–16) | 521 | 9.5 (3–22) | 4.50 (2.87 to 6.13) |
| DAS28-CRP | 817 | 3.95 (2.88–5.02) | 521 | 3.60 (2.65–4.53) | −0.35 (−0.56 to −0.15) |
| HAQ | 1010 | 0.75 (0.25–1.38) | 616 | 0.88 (0.38–1.63) | 0.13 (0.01 to 0.24) |
| RF status | 891 | 553 | |||
| Positive, n (%) | 252 (28.3) | 201 (36.4) | OR 1.45 (1.15 to 1.82) | ||
| Anti-CCP2 status | 759 | 511 | |||
| Positive, n (%) | 178 (23.5) | 161 (31.5) | OR 1.50 (1.17 to 1.93) | ||
| Met 2010 RA criteria, n (%) | 614 (60.1) | 347 (55.0) | OR 0.81 (0.66 to 0.99) | ||
| Current sDMARDs use, n (%) | 153 (15.0) | 278 (44.1) | OR 4.47 (3.54 to 5.65) | ||
| Treatment delay, months | 565 | 9 (4–22) | 471 | 6 (3–12) | −3.2 (−4.6 to –1.9) |
*Quantile/logistic/negative binomial regression was used to compare the two cohorts on each variable depending on the type of variable. Cohort 1 is the reference category.
†Multinomial logistic regression used to compare smoking status between cohorts. Never smoking is the base outcome and cohort 1 is the reference category.
anti-CCP2, anticyclic citrullinated protein antibodies; CRP, C reactive protein; DAS28, Disease Activity Score (28); HAQ, Health Assessment Questionnaire; n, number of patients with available data; RA, rheumatoid arthritis; RF, rheumatoid factor; RRR, relative risk ratio; sDMARD, synthetic disease-modifying antirheumatic drugs.