Background The ASAS classification criteria for axial spondyloarthritis (axSpA) allow two possible entrances: the imaging arm (presence of sacroiliitis) and the clinical arm (presence of HLA B27). Additionally, patients from the imaging arm can be classified as non-radiolographic axial spondyloarthritis (nr-axSpA) and ankylosing spondylitis (AS). The concept of nr-axSpA as well as the use of the clinical arm to calssify patients with SpA are currently under discussion. Therefore, it is necesary to investigate whether or not these patients have similar characteristics compared to the classical AS.
Objectives To describe and compare the characteristics of patients fulfilling the ASAS criteria for nr-axSpA versus patients with AS in an early disease cohort. Secondly, the characteristics of patients in the two axSpA arms (clinical and imaging) were compared too.
Methods Baseline dataset from the EsPeranza cohort was used. This cohort included patients from 25 Spanish centers with the following referral criteria: age <45 years, symptoms duration 3-24 months and with inflammatory back pain (IBP) or asymmetrical arthritis or spinal/joint pain plus ≥1 SpA features. Patients meeting ASAS axSpA criteria were included for this study. Demographic and clinical characteristics, activity indices (BASDAI and CRP), mobility (BASMI) and physical function (BASFI) were compared between groups.
Results A total of 291 axSpA patients were included. From these, 194 (67%) fulfilled the imaging arm (44% axSpA-nr and 56% EA), and 97 (33%) the clinical arm. Significant differences between AS and nr-axSpA patients were just observed for the following variables: gender (higher frequency of males in AS), diarrhea/genitourinary symptoms (more frequent in nr-axSpA), physician's VAS (higher in AS) and BASMI (lower in AS) (Table). No significant differences between both groups were found for the rest of variables. Moreover, patients in the clinical arm had significantly more diarrhea/genitourinary symptoms, peripheral arthritis, enthesitis, uveitis and family history of SpA compared with patients in the imaging arm. Physical function was more impaired in patients on imaging arm.
Conclusions Overall, patients with nr-axSpA have similar clinical features than those observed in AS patients in the early stages of the disease. However, the mobility in AS patients is more restricted. Furthermore, patients with axSpA in the clinical arm present more often peripheral involvement, uveitis and family SpA history as well as better function than patients in the imaging arm.
Acknowledgements The EsPeranza Program has been supported by Spanish Rheumatology Foundation and an unrestricted grant from Pfizer.
Disclosure of Interest : None declared