P004 Difficult to Treat axial Spondyloarthritis- insights from a tertiary rheumatology service

Abstract Background Therapy non-response (NR) can be seen in 30% of axial spondyloarthritis (axSpA) with some patients requiring multiple therapies. We wanted to assess in our axSpA population those with difficult to treat (D2T) disease as defined in two ways: (ever) failure of any 2 b/ts-DMARDs which we called “standard definition” or (ever) failure ≥2 b/ts-DMARDs with differing mechanisms of action (MoA), “strict definition”. Aims To describe the clinical, laboratory and imaging characteristics of axSpA patients meeting varying definitions of D2T disease and to compare differences between those responding to their current b/tsDMARD (BASDAI <4) and those who are not (BASDAI ≥4). Methods A cross-sectional analysis of b/ts-DMARD prescribing in the Leeds Specialist Spondyloarthritis Service identified patients with axSpA treated with a b/ts-DMARD between October 2023 and May 2024. Demographics and clinical characteristics including BASDAI, CRP and imaging were assessed. Patients were classified as NR at the time of assessment based if BASDAI ≥4, as a marker of ongoing disease activity. Results Overall, 680 patients on b/ts-DMARDs were identified, of which 109 (16.0%) had (ever) failed any 2 b/ts-DMARDs and 58 (8.5%) ≥2 b/ts-DMARDs with differing MoA. The demographics were similar between groups with mean age (49.2 [SD12.4] vs 49.5 [SD12.3]), predominant male sex (62% vs 65%), HLA-B27 (77% vs 81%), and prevalence of radiographic disease (59% vs 56%) in those meeting standard and strict definitions respectively. At last clinical review, 99 (91%) patients meeting standard definition and 51 (88%) meeting strict definition remained on a b/ts-DMARD. Of the patients reviewed during 2023/2024, 40/55 (73%) meeting the standard definition and 18/25 (72%) meeting the strict definition had NR. In patients experiencing NR, 17/35 (49%) had CRP >5 mg/L in the standard definition compared to 7/15 (47%) in the strict definition. Active inflammation on MRI was found on 1/4 patients meeting the standard criteria and 0/2 patients meeting the strict criteria. All patients had non-axSpA related pathology on MRI. Conclusions In this cross-sectional assessment a small proportion of axSpA patients appear to have D2T disease according to above definitions. Objective evidence of inflammation was seen in less than 50% either by CRP, MRI or both, suggesting a mix of non-inflammatory and true refractory disease. Further characterization of these populations in this and larger cohorts may identify predictors of non-response to b/tsDMARD therapy in axSpA.