Compared with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Ankylosing Spondylitis Disease Activity Score (ASDAS) definition for high disease activity is more inclusive in selecting patients with axial spondyloarthritis (axSpA) for treatment with biologic disease-modifying antirheumatic drugs (bDMARDs), according to research results published in RMD Open.

Researchers conducted a prospective multicenter cohort study of patients with axSpA to compare the BASDAI and ASDAS definitions of high disease activity when selecting patients for treatment with bDMARDs. Adults aged ≥18 years who registered with the Rheumatic Diseases Portuguese Register between June 2008 and May 2018 were eligible for inclusion in the study.

A total of 594 patients fulfilled the inclusion criteria (eligible population) with complete ASDAS and BASDAI data at baseline and 6 months of follow-up. Among these patients, 529 were starting treatment with their first bDMARD and 359 had complete data for all response outcomes at every timepoint (efficacy population).

Based on baseline characteristics, the investigators found that the probability of meeting the ASDAS definition of high disease activity (cutoff, ≥2.1) was higher than the probability of meeting the BASDAI definition of high disease activity (cutoff, ≥4; 93% vs 83%) among the eligible population. While most patients met the criteria for both definitions, some patients did not meet the criteria for either definition (82% vs 7%). Compared with patients who fulfilled both definitions, patients who fulfilled only the ASDAS definition were more likely to be men, who tested positive for HLA-B27, had higher levels of C-reactive protein, and lower Bath Ankylosing Spondylitis Functional Index.

Investigators assessed the adjusted response to bDMARDs at 3 and 6 months across 4 disease activity subgroups. Overall, they observed that patients responded well to bDMARDs, with outcomes largely overlapping between patients with high disease activity according to the ASDAS definition, irrespective of BASDAI. The likelihood of response for the most “difficult” to achieve outcomes, including Assessment of SpondyloArthritis international Society partial remission and ASDAS inactive disease, was significantly higher in a subgroup of patients who fulfilled the ASDAS definition alone compared with those who fulfilled both the ASDAS and BASDAI definitions.

Among the eligible population, 463 patients fulfilled the ASAS classification criteria for axSpA, of whom 286 were starting their first bDMARD therapy and had complete data for all outcomes. Patients in these populations demonstrated similar baseline characteristics and similar sensitivity analysis results.

Study limitations included the small number of eligible patients because of missing data, the researchers’ inability to meaningfully assess the efficacy of bDMARDs in patients who did not meet either criteria, and to the lack of investigating potential differences between patients with radiographic and nonradiographic axSpA.

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“[B]oth BASDAI and ASDAS perform well in selecting patients with axSpA for treatment with bDMARDs in daily clinical practice,” the researchers concluded. “Ignoring ASDAS as a selection criterion yields an unacceptable number of patients being excluded from an intervention from which they would most likely benefit…ASDAS should be at least used in addition to BASDAI, and most likely exclusively, when selecting patients for treatment with bDMARDs.”

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Marona J, Sepriano A, Rodrigues-Manica S, et al. Eligibility criteria for biologic-disease modifying antirheumatic drugs in axial spondyloarthritis: Going beyond BASDAI. RMD Open. 2020;6(1).