To evaluate the utility of the duration of morning stiffness (MS), as a patient-reported outcome (PRO), in assessing rheumatoid arthritis (RA) disease activity.
We acquired information on 5439 patients in QUEST-RA, an international database of patients with RA evaluated by a standard protocol. MS duration was assessed from time of waking to time of maximal improvement. Ability of MS duration to differentiate RA activity states, based on Disease Activity Score (DAS)28, was assessed by analysis of variance; and a receiver-operating characteristic (ROC) curve was plotted for discriminating clinically active (DAS28 > 3.2) from less active (DAS28 <or= 3.2) RA. Mixed-effect analysis of covariance (ANCOVA) models were used to assess the utility of adding MS duration to Routine Assessment of Patient Index Data (RAPID)3, a PRO index based on physical function, pain, and general health (GH), in predicting the 3-variable DAS28 (DAS28v3).
MS duration had moderate correlation (r = 0.41-0.48) with pain, Health Assessment Questionnaire, and GH; and weak correlation (r = 0.23-0.39) with joint counts and erythrocyte sedimentation rate. MS duration differed significantly among patients with different RA activity (p < 0.001). The area under the ROC curve of 0.74 (95% CI 0.72-0.75) showed moderate ability of MS duration to differentiate clinically active from less active RA. ANCOVA showed significant interactive effects between RAPID3 and the MS duration categories (p = 0.0005) in predicting DAS28v3. The effect of MS was found to be clinically important in patients with the low RAPID3 scores (< 6) in whom the presence of MS may indicate clinically active disease (DAS28v3 > 3.2).
MS duration has a moderate correlation with RA disease activity. Assessment of MS duration may be clinically helpful in patients with low RAPID3 scores.