Abstract
BackgroundThe relationship between non-radiographic axial spondyloarthritis (nr-axSpA) and ankylosing spondylitis (AS) is currently debated. Using observational data from the South Swedish Arthritis Treatment Group register, we thus aimed to compare clinical development and treatment adherence between nr-axSpA and AS patients during three years of anti-TNF (tumor necrosis factor) therapy in clinical practice, and to explore the impact of inflammatory activity measured by CRP (C-reactive protein) at treatment initiation.MethodsNr-axSpA and AS patients (n = 86/238) in southern Sweden, commencing anti-TNF therapy 1999-2011, were followed during three years. Anti-TNF cessation was defined as stopping therapy, without restarting another anti-TNF agent within three months. Differences in the three year developments of patient’s visual analogue scale (VAS) scores for global health and pain, EuroQol 5-Dimensions utility, evaluator’s global disease activity assessment, CRP, and ESR (erythrocyte sedimentation rate) were assessed by repeated ANOVA. Anti-TNF adherence was compared by Log rank test and Cox regression. In a subanalysis, the same outcomes were studied after splitting both groups into patients with/without baseline CRP elevation.ResultsNr-axSpA patients were more often female and had lower acute phase reactants at baseline. Apart from CRP, which remained lower in the nr-axSpA group throughout follow-up (p = 0.004), no between-group differences were detected regarding clinical developments (p >0.1 for all comparisons) or anti-TNF adherence (hazard ratio: 1.1 (95 % CI 0.7 to 1.8) for the nr-axSpA vs. AS group) during three years. Elevated baseline CRP was similarly associated with superior clinical outcomes and treatment adherence in both groups.ConclusionsWith the exception of constantly lower CRP levels in the nr-axSpA group, three years anti-TNF therapy resulted in similar clinical outcomes and treatment adherence in nr-axSpA and AS patients, thus strengthening the hypothesis that these diagnoses represent different aspects/phases of the same disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-015-0897-6) contains supplementary material, which is available to authorized users.
Highlights
The relationship between non-radiographic axial spondyloarthritis and ankylosing spondylitis (AS) is currently debated
The included nr-axSpA patients were all followed at the central South Swedish Arthritis Treatment Group (SSATG) university clinic in Lund/Malmö, did not have a clinical diagnosis of psoriatic arthritis, and based on data collected on initiation of anti-tumor necrosis factor (TNF) therapy - fulfilled the Assessment of SpondyloArthritis International Society (ASAS) classification criteria for axial spondyloarthritis, without having skin psoriasis or radiographic sacroiliitis on conventional radiographs (48 and 38 patients, respectively, according to the imaging and clinical arms) [3]
Treatment decisions were taken by the responsible rheumatologists, and no formal disease activity level was required for initiation of anti-TNF therapy
Summary
The relationship between non-radiographic axial spondyloarthritis (nr-axSpA) and ankylosing spondylitis (AS) is currently debated. Using observational data from the South Swedish Arthritis Treatment Group register, we aimed to compare clinical development and treatment adherence between nr-axSpA and AS patients during three years of anti-TNF (tumor necrosis factor) therapy in clinical practice, and to explore the impact of inflammatory activity measured by CRP (C-reactive protein) at treatment initiation. Spondyloarthritis (SpA) comprises a range of rheumatic disorders - ankylosing spondylitis (AS), undifferentiated SpA, psoriatic arthritis, arthritis related to inflammatory bowel disease, reactive arthritis, and a juvenile form sharing common clinical features, extraarticular manifestations, and a genetic association with the type 1 major histocompatibility complex HLA-B27. Display similar axial symptoms and signs of active sacroiliitis on magnetic resonance imaging (MRI) in the absence of such radiographic changes [2], entailing a risk of delayed or missed diagnosis. The observation that 10–12 % of nraxSpA patients progress to develop AS within 2 years, strengthens the hypothesis that the two entities represent different aspects/phases of a common pathology [9, 11]
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