Background/Purpose: Disease activity (DA) can change markedly over a short period, for a variety of reasons. The changes influence clinical practice and affect the willingness of patients to change their current treatment (WCT). However, impact cannot be examined in a cross-sectional study and is difficult to explore when DA is measured at only two points. This study measured DA at multiple points, distinguished observation-level DA from its patient-level trajectory, and examined the influence of both on WCT.

Methods: RA patients who were taking at least one DMARD and currently experiencing at least moderate pain were recruited from community-based rheumatology practices. They participated in four interviews over a six month period. DA was measured at each interview, using the Rapid-4. Scores were rounded up to single points. Patient-level trajectories were created, consistent with the rules described in Table 1, and each trajectory was coded as a nominal category. WCT was measured at each interview on a 10-point scale. Patient-level trajectory and observation-level Rapid-4 were examined by linear mixed models and were compared using AIC, a lower-is-better goodness of fit test.

Results: N=142 patients participated. Their mean age was 59, mean duration of RA was 12.8 years; 86% were female and were 81% were Caucasian. As the table indicates, 46% of patients were stable, 20% were getting better, 17% were getting worse, and 18% were fluctuating. Observation-level Rapid-4 was significantly associated with WCT (F=5.42, df= 3/433, p=.001). Its interaction with the patient-level trajectory was also significant (F=2.55, df=15/354, p=.001) and offered the best fit (AIC is about 2% lower). Trajectory alone was non-significant and provided the worst fit of the 3 models. The figure shows estimated WCT at each Rapid-4 category for the stable and fluctuating trajectories. One exhibits a small variation from mild to moderate; the other increases markedly at mild, then levels out.

Conclusion: Patient- and observation-level DA have a combined influence on WCT. Despite marked differences, stable and fluctuating trajectories would not be distinguished if DA were assessed at only two points.