Sensitivity and discriminatory ability of the Ankylosing Spondylitis Disease Activity Score in patients treated with etanercept or sulphasalazine in the ASCEND trial

Objectives. The Ankylosing Spondylitis Disease Activity Score (ASDAS) is a new composite clinical tool combining subjective and objective measures. Using data from the randomized double-blind Ankylosing Spondylitis Study Comparing Enbrel with Sulfasalazine Dosed Weekly (ASCEND) trial, we tested ASDAS validity and assessed its capacity to discriminate between treatment effects and change-from-baseline improvements. Methods. These post hoc analyses were conducted in patients who received etanercept (50 mg/week) or SSZ (3 g/day) for 16 weeks. The ASDAS was tested for its capacity to discriminate between those who achieved and did not achieve Assessment of Spondyloarthritis International Society (ASAS) partial remission and ASAS20. Week 16 adjusted treatment differences and effect sizes of improvement from baseline of 42 outcomes were calculated. Results. Means for ASDAS were less than half in patients with ASAS partial remission compared with patients without partial remission across the entire study population (1.2 vs 2.6; P < 0.0001). Patients who achieved ASAS20 had greater mean changes from baseline in ASDAS than those who did not (-1.8 vs -0.3; P < 0.0001). ASDAS was consistently shown to have one of the highest discriminatory capacities compared with other measurements (including subjective measurements) regardless of normal vs high CRP, presence or absence of peripheral arthritis and high vs very high ASDAS at baseline. As a dichotomous variable using different thresholds for improvement and disease severity, ASDAS had slightly better discriminatory capacity than all corresponding ASAS measures. Conclusion. ASDAS is a validated and highly discriminatory tool for the detection of significant differences between treatments for AS as well as for detecting a significant improvement from baseline with etanercept and SSZ.