Background: Non-radiographic axial spondyloarthritis (SpA) is emerging as a treatable disease comparable to ankylosing spondylitis (AS), but less well studied. Previous studies have described a reversed gender distribution, with AS being more prevalent in the male population and non-radiographic axial SpA more prevalent in the female population. Recent studies have also indicated a similar benefit from treatment with TNF-inhibitors.

Objectives: The aim of this study was to estimate the prevalence of non-radiographic axial SpA and compare the patient reported outcome measures (PROMS) to that of AS, in Southern Sweden.

Methods: All health care seeking individuals, ≥18 years, given a SpA-diagnosis, according to the ICD-10 (M45.9, M072, M460, M461, M468, M469, M074, M705 and L405 or M071 or M073), either in primary or specialized care, (N = 5771), during 2003 - 2007, were identified through the regional health care register in Skåne, a county in Southern Sweden with 1.2 million inhabitants (SpAScania cohort). In 2009 they were all sent a questionnaire (response rate; 48%), including questions concerning inflammatory back pain (IBP), the SpA-associated comorbidities constituting the ASAS-criteria (IBD, Ps, Uveitis/tendinitis, heredity), PROMS (BAS-indices, VAS-pain/fatigue/global, EQ5D) and previous/current medication.Non-AS axial SpA was defined as having an ICD10 code supporting a diagnosis of SpA without having one of AS (M45.9), in combination with > 3 months of back pain the last year and the presence of ≥2 of the SpA associated comorbidities. Record review support the notion of using AS as a substitute for radiographic changes. For the “non imaging arm” of the ASAS criteria for axial disease, we used the ICD10 codes above as a substitute for HLA-B27 status. Assuming similar answers from the questionnaire non-responders, prevalence rates were estimated for non-AS axial SpA and AS.

Results: Among responders 742 had an AS-diagnosis and 640 fulfilled the study criteria for non-AS axial SpA. The frequency of men was 60.5% in the AS group and 29.5% in the non-AS axial SpA group. The prevalence of AS was 0.13% (95% CI; 0.115-0.148) and for non-AS axial SpA 0.11 % (95% CI; 0.096-0.130), with a reverse gender distribution. The means of the PROMs and frequency of comorbidities were higher in the non-AS axial SpA vs both the AS, and the subgroup of AS individuals reporting back pain (BP) > 3months during the last year. Self-reported present use of TNF-inhibitors were similar between the groups (Image 1).

Conclusions: Prevalence rates for AS and non-AS axial SpA were similar, with a reverse gender distribution. The results suggest that at a population level the proportion with non-AS axial SpA is at least as large as that of AS and report lower levels of perceived health status and similar frequencies of SpA-related comorbidities (except psoriasis) and treatment with TNF-inhibitors, supporting the validity for the used definition in future research.

Disclosure of Interest: None Declared