Prevalence of chronic widespread pain in a population-based cohort of patients with spondyloarthritis – a cross-sectional study

BACKGROUND: Chronic pain, regional or widespread, is a frequent and multidimensional symptom in arthritis. There is still limited information on chronic pain in spondyloarthritis, which is important to recognize for adequate diagnosis and treatment. Our objective was to study differences in prevalence of chronic widespread pain in two spondyloarthritis subgroups: ankylosing spondylitis (AS) and undifferentiated spondyloarthritis (USpA). METHODS: A population-based postal survey involving questions on the duration, distribution, and intensity of pain was answered by 940 patients with AS (ICD-10 M45.9) or USpA (ICD-10 M46.1-0, M46.8-9). The patients were categorized as having chronic widespread pain, chronic regional pain, or no chronic pain, and prevalence estimates for the pain groups were calculated, including age- and sex-adjusted prevalence. RESULTS: The prevalence of chronic widespread pain was 45.3% in AS vs. 49.3% in USpA, and that of chronic regional pain was 17.7% vs. 21.9% (p = 0.033). More women than men reported having chronic widespread pain (54.1% vs. 41.2%, p ≤ 0.001), while the sex distribution for chronic regional pain was equal. Reports of pain intensity were equal in AS and USpA, with no significant difference in pain intensity between women and men who had chronic regional pain or chronic widespread pain. In the multiple logistic regression analysis, chronic widespread pain was associated to female sex, being an ever-smoker, and having a higher body mass index, controlled for SpA subgroup and disease duration. CONCLUSIONS: The prevalence of chronic widespread pain in patients with AS and USpA is high, and with a female predominance, but with no difference in pain intensity between women and men. Chronic pain can complicate the clinical evaluation in patients with SpA, and highlights the need for a thorough clinical examination, including evaluation of inflammation and an accurate pain analysis, to individualize non-pharmacological and pharmacological treatment decisions.