Background Several outcome measures in trials with juvenile-onset spondyloarthritis (Jo-SpA) have been borrowed from trials in juvenile idiopathic arthritis and from adult spondyloarthritis, but a proper psychometric analysis has never been conducted in patients with Jo-SpA.
Objectives To assess discriminatory aspects of several disease activity outcome measures and response criteria for Jo-SpA.
Methods Data from a previously reported 12-week RCT comparing infliximab (IFX) and placebo (PBO) in patients <18 years with Jo-SpA and onset <16 years of age were analyzed. The primary endpoint of the trial was the number of active joints (both swollen and tender). Several other disease activity measures and response criteria were also tested (Table). Statistics to determine how well disease activity measures could discriminate between IFX and PBO included “standardized mean difference” (SMD) and “Guyatt's effect size”. Both statistics are standardized measures to compare change from baseline per group. For categorical response criteria, the chi-square test (χ2) was used. Higher numbers indicate better discriminatory capacity.
Results Patients were randomised to IFX (n=12) and PBO (n=14). Of the continuous measures, the ASDAS showed the best and very good discrimination between IFX and PBO (SMD:1.98; Guyatt: 4.28) (Table). The physician's global, CRP, JADAS and JSpADA also discriminated well. The BASDAI (or its separate items), BASFI and spinal mobility measures performed worse. Of the response criteria ASAS40 and ACR Pedi 90 discriminated best between IFX and PBO (Table). ASDAS response criteria and ACR Pedi 30–70 also performed well.
Conclusions Of all continuous measures tested in adult axial SpA the ASDAS discriminates best between active treatment and PBO in patients with Jo-SpA. But the child specific JSpADA also performs well.
Of all response criteria tested the child-specific ACR Pedi 30 to 90, as well as the adult ASAS40 and ASDAS response criteria work well. One of these measures should be used as primary endpoint in trials with Jo-SpA.
Acknowledgement Schering-Plough Mexico funded this trial as an investigator-initiated study
Disclosure of Interest None declared