Background/Purpose: Pain remains a common and debilitating symptom in arthritis, despite good options to treat inflammation. In axial spondyloarthritis (axSpA), data on chronic pain remain scarce. 

Objective: To assess self-reported and observed aspects of pain in subgroups of axial spondyloarthritis (axSpA), and to investigate associations between these pain aspects and different health outcome measures. 

Methods: A cross-sectional study of patients with axSpA (ankylosing spondylitis (AS) and undifferentiated spondyloarthritis (USpA, based on ICD10 codes)), consecutively enrolled in the SPARTAKUS cohort (n=226). Of 197 patients, for whom all relevant information was available, 173 patients fulfilled the ASAS axSpA criteria, and 115 the modified New York criteria. We investigated self-reported pain (intensity, duration, and distribution) and categorized patients into chronic widespread pain, chronic regional pain and no chronic pain. In addition, pain sensitivity (pain threshold, pain tolerance and temporal summation of pain), was assessed by computerized cuff pressure algometry (CPA). Comparisons between AS and USpA and between women and men were performed using Student`s t-test or Chi-squared test. Associations of pain sensitivity measures and different health outcome measures, adjusted for age and sex, were analyzed by multivariate linear regression. 

Results: All assessed pain measures, except for number of pain regions, were similar in AS and USpA. Almost 50% of the axSpA patients, reported chronic widespread pain (AS 42%, USpA 53%), which was more pronounced in women (60% vs. 34% for men, p<0.001). For pain sensitivity measures, women had lower pain tolerance as compared to men (AS (p=0.03), USpA (p=0.01)), while pain threshold was lower only for women with USpA (p<0.01) (Table). Furthermore, irrespective of diagnosis subgroup, lower pain tolerance was associated with higher disease activity, more fatigue and less spinal mobility. 

Conclusion: In this population-based, cross-sectional study of established axial spondyloarthritis, chronic widespread pain was common, affecting 50% of the patients. A clear sex difference was found, with women reporting worse measures for both self-reported pain and pain sensitivity. Overall, lower pain tolerance was associated with worse disease activity, fatigue and spinal mobility. CPA shows promising results regarding assessment of pain sensitivity and provides additional information in pain evaluation in AxSpA. © 2018 American College of Rheumatology