Is swollen to tender joint count ratio a new and useful clinical marker for biologic drug response in rheumatoid arthritis? Results from a Swedish cohort.

OBJECTIVE To study the impact of swollen to tender joint count ratio (STR) and other baseline characteristics on treatment response to a first course of anti-tumor necrosis factor (anti-TNF) therapy in rheumatoid arthritis (RA) patients. METHODS Patients with RA initiating their first course of anti-TNF treatment were included in a structured clinical followup protocol. Based on pragmatic thresholds and plausibility, patients were categorized as having low (STR <0.5), moderate (0.5 ≤ STR ≤ 1.0), or high (STR >1.0) joint count ratios. The data were collected and followed during the period of March 1999 through December 2010. RESULTS A total of 2,507 patients were included in the study (median age 56 years, 78% women). Of these patients, 344 (14%) had a low STR, 1,180 (47%) had a moderate STR, and 983 (39%) had a high STR. According to these STR thresholds, 23% of patients (95% confidence interval [95% CI] 18-29%) with low, 39% (95% CI 35-43%) with moderate, and 40% (95% CI 36-44%) with high STR achieved the American College of Rheumatology criteria for 50% improvement (ACR50) response at 6 months after initiation. Correlation tests showed that STR was associated with ACR50 response independent of both swollen and tender joint counts. Logistic regression analysis consistently showed that moderate STR, high STR, not using prednisolone, high baseline Disease Activity Score in 28 joints, and low baseline Health Assessment Questionnaire scores were significantly associated with favorable ACR50 response with odds ratios of 1.93 (P < 0.01), 2.82 (P < 0.01), 0.65 (P < 0.01), 1.49 (P < 0.01), and 0.47 (P < 0.01), respectively. CONCLUSION STR is a new and feasible predictor of treatment response in RA. RA patients with a moderate to high STR have a 2- to 3-fold increased likelihood of responding according to ACR50 criteria.