Morning stiffness (MS) is a common problem for patients with rheumatoid arthritis (RA). However the clinical evaluation of the symptom has proved to be difficult. The aim of the study was to determine the responsiveness of two methods for measuring MS.
Data from an uncontrolled (n = 63) and a controlled study (n = 80) of inpatient multidisciplinary team care for RA were analyzed. MS was measured by its duration to maximum improvement and by its severity on a visual analog scale (VAS). The responsiveness of both assessment methods was computed by calculating effect sizes and t-statistics, and by receiver operating characteristic (ROC) curves with clinical improvement according to the definition of the American College of Rheumatology as an external criterion.
With respect to the ability to detect a clinical improvement between admission and discharge in the uncontrolled study, and a difference in improvement between the treatment and the control group in the controlled study, the effect sizes and t-values of the VAS for severity of MS were consistently higher than those of the duration of MS. In contrast to the duration, the responsiveness of the VAS for MS compared favorably with the responsiveness of other endpoint measures. The ROC surface area of the VAS was higher than that of the duration.
For the evaluation of MS in RA clinical trials, the assessment of MS by a severity score is more responsive than one based on duration and compares favorably with the performance of other endpoint measures.