Severe low back pain in patients with rheumatoid arthritis is associated with Disease Activity Score but not with radiological findings on plain X-rays

Objective. To investigate the prevalence and associated factors of severe low back pain (LBP) among patients with rheumatoid arthritis (RA). Methods. This cross-sectional study included 201 patients with RA without prior spinal surgery. Severe LBP was defined as that with a visual analog scale (VAS) score of >= 50 mm within the previous 4 weeks. Lumbar lesions, sagittal alignment, and disc degeneration were evaluated by plain standing X-rays and magnetic resonance imaging. Associated factors of severe LBP were evaluated using multiple logistic regression analysis. Results. Forty-eight patients (23.8%) had LBP with a VAS score of >= 50 mm. Multivariate analysis indicated that the associated factors for severe LBP were female, smoking, and moderate and high disease activity on the Disease Activity Score in 28 joints-erythrocyte sedimentation rate (DAS28-ESR). There was no relationship between severe LBP and any radiological findings. Among DAS28-ESR subscores, patients with severe LBP had significantly higher tender joint counts and VAS scores for general health. Conclusions. The prevalence of severe LBP was relatively high in patients with RA. The factor most closely associated with severe LBP was Disease Activity Score, but not radiological findings. Severe LBP was related to the tender joint count or subjective complaints of RA.