Applying the ASAS definition of difficult-to-manage and treatment-refractory axial spondyloarthritis: an exploratory single centre cross-sectional study

The Assessment of SpondyloArthritis International Society (ASAS) has recently proposed a consensus-based expert definition for difficult-to-manage (D2M) axial spondyloarthritis (axSpA) and treatment-refractory (TR) axSpA. Our aim is to determine the proportion of D2M and TR axSpA according to the ASAS definition and describe the characteristics of these patients. We conducted an observational cross-sectional single-centre study that included all adult patients with axSpA, meeting the ASAS classification criteria, exposed to biologic or targeted synthetic disease-modifying anti-rheumatic drugs (b/tsDMARDs). D2M axSpA was defined according to the ASAS criteria as 1) treatment according to the ASAS-European alliance of associations for rheumatology recommendations and failure of ≥2 b/tsDMARDs with different mechanisms of action (MoA), 2) insufficient control of signs/symptoms of axSpA (axial spondyloarthritis disease activity score (ASDAS)≥2.1 or C-reactive protein (CRP)>5.0mg/L or active inflammation on magnetic resonance imaging (MRI) or radiographic progression) and 3) the signs/symptoms are perceived as problematic by the patient/physician (patient/physician global assessment ≥4/10). TR axSpA was a subset of D2M axSpA in which 1) the use of ≥2 b/tsDMARDs was due to treatment failure, 2) with high or very high disease activity (ASDAS≥2.1) plus evidence of inflammatory activity (CRP>5.0mg/L or MRI showing active inflammation) and 3) other causes of signs and symptoms excluded. The proportion of D2M and TR axSpA was estimated. Descriptive analysis of axSpA, D2M, and TR was performed, and an exploratory analysis to compare D2M vs non-D2M axSpA. We included 207 patients, of whom 2.9% (n=6) met the criteria for D2M axSpA and 1.4% (n=3) for TR axSpA. Among axSpA patients, 52 (25.1%) had prior treatment with ≥2 b/tsDMARD, but only 12 (5.8%) had different MoA. Additionally, 42.8% (n=86) and 38.3% (n=77) fulfilled the second and third criterion for D2M axSpA, respectively, but only 13.2% (n=26) met the second criterion for TR axSpA. D2M axSpA was associated with a younger age at symptom onset and diagnosis. Applying the ASAS definition, we found a low proportion of D2M and TR axSpA. The first criterion (≥2 b/tsDMARDs with different MoA) limited the classification of patients as D2M or TR. This is among the first studies applying the ASAS definition.