Testing thresholds in cases of axial spondyloarthritis: Is the ASDAS appropriate for everyday clinical practice?

In patients with axial spondyloarthritis (axSpA) and persistent disease activity for which adapting treatment is recommended, treatment intensification should be considered for patients with persistently high disease activity. EULAR—The European Alliance of Associations for Rheumatology—in collaboration with the Assessment of SpondyloArthritis international Society (ASAS), states that high disease activity should be based on a composite score, the Ankylosing Spondylitis Disease Activity Score (ASDAS) with a cutoff ≥2.1.

However, this recommendation is not always followed in practice. This could be because the ASDAS was developed for research, and it is not known how well it performs in daily practice. Possibly, the cutoff of 2.1 as currently endorsed may be too strict in an everyday setting. To address this, researcher Casper Webers and colleagues set out to investigate which ASDAS cutoff values correspond best with treatment intensification in practice.

Data were taken from a prospective multi-center registry for SpA, and treatment intensification was defined as either higher dose or frequency of the same drug, switch to another drug, or addition of a new drug to the regimen—all due to inefficacy. Analyses were conducted both with all observations, and again with only the first observation per patient per calendar year, in order to achieve a balanced number of observations per patient by follow-up duration. Overall, 350 patients with 2,265 ASDAS measurements were included—and approximately two-thirds received a biologic or targeted synthetic disease-modifying antirheumatic drug (b/tsDMARD) at some point during follow-up.

The results, presented at the 2024 EULAR congress in Vienna, show that treatment intensification was applied after 10.4% of ASDAS measurements—and at the time of intensification, patients were often already on anti-inflammatory treatment. Treatment intensification often involved switching to another drug—typically within the same drug class—or adding a drug, and the use of conventional synthetic DMARD and corticosteroids was limited.

The mean ASDAS and proportion with ASDAS ≥2.1 was higher at intensification timepoints than at non-intensification timepoints. When all ASDAS measurements were included for analysis, the optimal ASDAS cutoff related to treatment intensification was 2.7, and results were similar when only one measurement was used per patient and calendar year. Of note, over the years, the optimal ASDAS cutoff varied substantially—from 2.3 to 2.8—but was consistently higher than 2.1.

The researchers conclude that in daily practice, treatment intensification is associated with a higher ASDAS cutoff value than the recommended one of 2.1. This could be because rheumatologists believe the recommended cutoff is too stringent, or consider factors other than disease activity when making treatment decisions. EULAR and ASAS recommend that treatment of axSpA should be individualized according to the current signs and symptoms of the disease, including axial, peripheral, and extramusculoskeletal manifestations—as well as each person's characteristics, such as comorbidities and psychosocial factors.