Background Chronic back pain is a prominent symptom in Spondyloarthritis (SpA), and an important contributor to diminished quality of life (1,2). Chronic pain can develop in intensity, become more spread, and progress to chronic widespread pain (2). Mechanisms for this are yet inconsistent (3), and in SpA, knowledge of progression to chronic widespread pain (CWP) is lacking.

Objectives To study the development of CWP in patients with SpA, and to identify risk factors for development and persistence of CWP.

Methods A cohort study with baseline and 2.5-year follow-up postal surveys. 644 patients (47% women) with ankylosing spondylitis (AS) and undifferentiated spondyloarthritis (SpA) answered both surveys, and were categorized as no chronic pain (NCP), chronic regional pain (CRP), and CWP. Logistic regression analyses, with CWP as the main outcome were performed. Due to multicollinearity, each risk factor candidate (disease duration, BMI, smoking, and different patient-reported outcome measures; PROMs) were analysed in separate logistic regression models together with a base model (age, sex, and SpA-subgroup).

Results At follow-up, prevalence estimates for NCP, CRP and CWP were similar to those at baseline, but 38% of the patients had transitioned between the groups. A large group, 72% of the patients with initial CWP, also reported persistent CWP at follow-up (Figure). Risk factors (OR and 95% CI) for development of CWP from initial NCP/CRP were more pain regions (1.36; 1.20–1.53), pain intensity (1.35; 1.20–1.52), fatigue (1.25; 1.13–1.38), global health (1.35; 1.19–1.54), EQ-5D (0.05; 0.01 – 0.19), BASDAI (1.25; 1.07 – 1.45), BASFI (1.32; 1.16 – 1.50), ASES pain (0.97; 0.96 – 0.99), ASES symtom (0.98; 0.97 – 0.99), and HADb (1.10; 1.02 – 1.19). The risk factors for persistent CWP, compared to patients transitioning to NCP or CRP, were similar to those predicting development of CWP, but in addition, also higher age (1.02; 1.00–1.04), and female sex (1.82; 1.06–3.10), predicted the outcome. © 2017 BMJ Publishing Group Limited.