Objective To assess the discriminative ability and correlation of the Ankylosing Spondylitis Disease Activity Score (ASDAS) and Bath Ankylosing Spondylitis Activity Disease Activity Index (BASDAI) with disease activity in axial psoriatic arthritis (AxPsA).
Methods Patients with AxPsA were selected from a large prospective cohort study of psoriatic arthritis. Patient and physician global scores were used as constructs of disease activity. Patients were categorised into high and low disease activity states based on patient and physician global assessment scores and physician's decision to change treatment. Statistical analysis included descriptive statistics, linear and logistic regression.
Results 201 patients with AxPsA were included in the study. ASDAS and BASDAI showed good correlation with disease activity as reflected by the patient global score (correlation coefficients (r) for BASDAI 0.84, ASDAS-B 0.77, ASDAS-C 0.81, p<0.001) and the physician global score (r=0.53 for BASDAI, r=0.50 for ASDAS-B, r=0.55 for ASDAS-C, p<0.001). Both scores showed good discriminative ability between high and low disease activity states. However, there were no significant differences between areas under the curve for the models that compared ASDAS with BASDAI for each definition of disease activity state.
Conclusions In patients with AxPsA, ASDAS and BASDAI scores show similar good to moderate discriminative ability and correlation with different constructs of disease activity. ASDAS was not superior to BASDAI in its ability to discriminate between high and low disease activity states in AxPsA.
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Funding The University of Toronto PsA program is supported by a grant from the Krembil Foundation as well as by The Arthritis Society SPARCC National Research Initiative. LE is supported by a Fellowship grant from the Canadian Arthritis Network and an Abbott PsA Fellowship. VC is supported by a Canadian Institutes of Health Research – Clinical Research Initiative Fellowship and the Krembil Foundation. RJC holds a Canada Research Chair in Statistical Methods for Health Research.
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the University Health Network Research Ethics Board.
Provenance and peer review Not commissioned; externally peer reviewed.