Assessment of pain in rheumatoid arthritis: Minimal clinically significant difference, predictors, and the effect of anti-tumor necrosis factor therapy

Objective. To compare a visual analog pain scale (VAS) with the Medical Outcomes Study Short Form36 Health Survey (SF-36) bodily pain; to define the minimal clinically important change (MCIC) for pain in observational studies; to define clinically useful cutpoints for pain; to quantify the predictors of pain; and to estimate the effect of anti-tumor necrosis factor (TNF) therapy on pain. Methods. Over 6 years we studied 12,090 patients with rheumatoid arthritis (RA). Pain was assessed by VAS and SF-36 pain scales. Results. Compared with the SF-36 scale, the 0-10 VAS pain scale was better correlated with all clinical variables. The mean VAS score was 3.4 (standard deviation 2.8), and the best cutpoint for an "acceptable" level of pain was <= 2.0. The MCIC for pain was approximately 0.5 units by one measure and 1.1 by another. Pain increased slightly with the duration of RA, 0.03 (95% confidence interval 0.02-0.03) and decreased with age, 0.01 (95% Cl 0.01-1.02) units per year. Pain was greater in ethnic minorities [0.78 (95% Cl 0.63-0.93)] and women [0.31 (95% Cl 0.23-0.39)] and was lower in college graduates [-0.88 (95% Cl -1.00 to -0.76)]. Self-reported joint and nonarticular pain at 16 bilateral sites explained 44% of VAS pain scores. Anti-TNF therapy reduced pain by 0.59 to 0.53 units and EuroQol utility by 0.02 (95% Cl 0.02-0.02) units. Conclusion. Anti-TNF therapy improved pain by 0.53 to 0.70 units. The MCIC for improvement and worsening of pain is about 0.5 to 1.1 units. Pain levels are almost constant over RA duration, and are increased in women, ethnic minorities, smokers, and those with less education.