0569: ASAS Recommendations on Reporting Outcomes of Core Outcome Set Instruments in Axial Spondyloarthritis Clinical Trials

Background/Purpose: The recently updated Assessment of SpondyloArthritis international Society (ASAS) core outcome set (COS)
includes an agreed minimum set of instruments that should be used in all axial spondyloarthritis (axSpA) trials.
However, recommendations on how to report outcomes of the 16 COS instruments is lacking.
Aim of the project is to develop expert endorsed recommendations on how outcomes of COS instruments should be reported.

Methods: A steering group (SG) (FvG, VNC, DvH) convened a workgroup (WG) consisting of thirteen ASAS members
including rheumatologists, methodologists, epidemiologists, and two Young ASAS (Y-ASAS) members (all other
co-authors). Recommendations on reporting instrument outcomes were developed in three steps: the SG
formulated a proposal on how outcomes related to the instruments should be presented. ii) the proposal was
presented, discussed and modified in a WG meeting. iii) the WG proposal was discussed and voted on by ASAS
members.

Results: Reporting 20 trial outcomes at baseline and follow-up timepoints are recommended: 10 for all clinical trials and
10 for DMARD trials only (Table). The most common format is to report the mean plus the standard deviation
(SD) at all timepoints while adding the mean change (SD) from baseline for each timepoint. For ASDAS it is
recommended to also report the number and percentage of patient with decrease of ≥1.1 and ≥2.0 units, an
increase of 0.9 for flares, and ASDAS status at all timepoints (inactive (< 1.3), low (≥1.3 and < 2.1), high (≥2.1 and
≤3.5), and very high ( >3.5) plus the number and percentage of patients with scores < 2.1 and ≥2.1). For ASAS
health index it is recommended to also report the number and percentage of patients with decrease in the
score of ≥3 and status (good (≤ 5), moderate (< 5 to < 12), and poor (≥12)) at all timepoints.
It is recommended for psoriasis, uveitis, and IBD to be reported as the number and percentage of patients with
flare or (re)occurrence since baseline plus the rate per 100 patient-years while also splitting the results by
patients with and without a history of that particular extra-musculoskeletal manifestations. For spinal
syndesmophytes it is recommended to report the number and percentage of patients with at least one at
baseline and outcomes plus the number and percentage of patients with a newly developed syndesmophyte
which, if not scored separately, can be derived from the mSASSS scoring with a vertebral unit over time
developing an mSASSS score of 2 or 3 from a score less than 2 counting as the development of a
syndesmophyte. At the 2024 annual ASAS workshop recommendations were voted in by 81 full ASAS members
with 85% in favour, 9% against, and 6% abstaining.

Conclusion: These ASAS endorsed recommendations provide a consensual approach to reporting outcomes of axSpA
clinical trials. Adherence to these recommendations will standardize presentation of results and thereby
provides better insight into trial outcomes and facilitate the comparison of outcomes across studies.