To determine whether the Patient Activity Scale-II (PAS-II) is a generic measure of disease activity by assessing whether the relationship of PAS-II with treatment decision (indicating disease activity) is invariant across disease.
The Health Assessment Questionnaire-II (HAQ-II), a 10 cm visual analog scale for "pain," and another for "patient global assessment" were recorded from 1000 consecutive patients attending rheumatology outpatient clinics. Active disease was defined as treatment intensity increased and inactive disease was defined as treatment intensity unchanged or decreased. A logistic regression analysis was conducted with active disease as the dependent variable and the predictor variables were PAS-II, diagnostic category, and the interaction between diagnostic category and PAS-II.
PAS-II had a weak but statistically significant association with active disease that was independent of diagnosis. An increase of 1 point in PAS-II increased the odds of being in the active disease state by 1.19 (95% CI 1.10 to 1.37). The relationship between active disease state and PAS was not affected by diagnostic category.
PAS-II can be used as a generic self-report indicator of active disease across different rheumatic disorders, and not just in rheumatoid arthritis. The strength of the relationship with disease activity is weak and physician-derived indicators remain very important.