Background/Purpose: Assessment of SpondyloArthritis international Society (ASAS) recommendations for use of TNF inhibitors (TNFi) in axial SpA include active disease and a positive expert opinion, which includes consideration of serum acute phase reactant and/or imaging results that indicate active inflammation and/or risk of radiographic progression. Little is known about the characteristics of patients (pts) with non-radiographic axial SpA (nr-axSpA) who fulfill criteria for TNFi use. Here we characterize the clinical phenotype of nr-axSpA pts enrolled in the ABILITY-3 adalimumab study in terms of ASAS classification criteria and parameters of objective inflammation at baseline.

Methods: ABILITY-3 enrolled adult pts with nr-axSpA defined as fulfilling ASAS classification criteria but not modified New York radiologic criteria for ankylosing spondylitis (AS). Pts were required to have a minimum baseline disease activity (defined as Ankylosing Spondylitis Disease Activity Score ≥2.1, BASDAI ≥4, and total back pain score ≥4), objective evidence of inflammation (in ≥1 of the following: MRI of the SI joints, MRI of spine, and/or elevated high-sensitivity CRP [each centrally evaluated]), and an inadequate response to ≥2 NSAIDs. Pts received open-label adalimumab 40 mg every other wk for 28 wks during period 1. Pts achieving sustained remission (wks 16–28) were randomized into the double-blind period 2. Here, we analyzed whether enrolled patients fulfilled the imaging arm of the ASAS classification criteria (sacroiliitis on imaging plus ≥1 SpA feature), the clinical arm (presence of HLA-B27 plus ≥2 SpA features), or both arms, and which objective parameters of inflammation were present.

Results: 673 of 1506 screened pts were enrolled; screen failures were commonly due to pelvic x-ray consistent with AS (24.7%), not fulfilling ASAS classification criteria (29.3%), or lack of objective evidence of inflammation (22.1%). Overall, 664 pts (98.7%) fulfilled the ASAS criteria, of which 447 (67.6%) fulfilled the imaging arm, 513 (77.4%) the clinical arm, and 296 (44.0%) both arms. At baseline, 662 (98.4%) pts had objective evidence of active inflammation. Most pts (74.0%) had evidence of MRI inflammation, 31.4% had MRI inflammation only, 42.6% were MRI positive and had elevated hsCRP, and 24.1% had elevated hsCRP only (Table).

Conclusion: An important proportion of screened nr-axSpA pts with clinically active disease did not present with objective measures of inflammation, and would not be candidates for biologics per ASAS recommendation. Many pts fulfilled both imaging and clinical arms of the ASAS criteria with more fulfilling the clinical vs imaging arm. Nearly 60% of pts who presented with MRI inflammation also had elevated hsCRP, suggesting hsCRP assessment as the first step in evaluating pts for objective inflammation due to low cost and ease of obtainment, unless MRI is required for diagnosis.