Multivariate relationships between pain intensity and other aspects of health in rheumatoid arthritis--cross sectional and five year longitudinal analyses (the Swedish TIRA project).

OBJECTIVES

This study analyses the relationships between pain intensity and other aspects of health commonly used to assess disease activity and disability in early rheumatoid arthritis and examines whether such relationships were different between women and men.

SUBJECTS AND METHODS

This study included the 189 patients (69% women) with early RA (symptoms <12 months at diagnosis) still remaining in the Swedish TIRA cohort 5 years after inclusion. Disease activity and disability was assessed 3, 6, 12, 18, 24, 36, 48, and 60 months (M0-M60) after inclusion by erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), number of swollen and tender joints, physicians global assessment of disease activity (PGA), grip force average over 10 seconds (Grippit), Grip Ability Test (GAT), Signals of Functional Impairment (SOFI) in hand, lower limb and upper limb, Health Assessment Questionnaire (HAQ), and pain intensity measured with a visual analogue scale (VAS). The variables were divided into meaningful blocks according to the correlation structure in a principal component analysis (PCA) at M60. Using hierarchical partial least squares (PLS) analyses, this study investigated the blocks cross-sectionally to test for correlations with pain intensity at M0 and M60. The blocks at M0 were also used as predictors of pain intensity at M60 in a hierarchical PLS.

RESULTS

The strongest relationship was found between pain intensity and the second block, consisting of HAQ and SOFI-lower limb at the cross-sectional analyses in both women and men. The block representing disease activity (i.e., ESR, CRP, PGA, and swollen and tender joints) had the weakest relation to pain intensity. According to the longitudinal analyses, the disease activity variables (block 1) at M0 had the strongest relationship to pain intensity at M60 in men. In contrast, HAQ and SOFI-lower limb (block 2) at M0 had a strong relation to pain intensity in women.