Could the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) be a valid measure of disease activity in patients with psoriatic arthritis?

Objective To determine whether the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) could be a valid indicator of disease activity in psoriatic arthritis (PsA). Methods Patients with PsA identified from a disease‐register and case‐note review answered a questionnaire by mail (n = 133); some patients (n = 86) consented to examination. In a second sample of 47 consecutive clinic attendees with PsA, logistic regression examined the independent contribution of BASDAI to disease activity, as judged by treatment decisions at that time. Results BASDAI correlated highly with patient perception of disease activity (r = 0.739) and there was no significant effect of the pattern of disease (axial or peripheral) on this relationship. However, only physician perception of disease activity was significantly associated with high or low disease activity (odds ratio 18.4, 95% confidence interval 2.9–118.3). BASDAI, patient perception, and erythrocyte sedimentation rate failed to contribute significantly to the model. Conclusion BASDAI performs similarly for axial and peripheral PsA but does not correlate well with external indicators of disease activity, such as treatment decisions.