Consistency of morning stiffness: an analysis of diary data

This study aimed to determine the within-individual daily variation in morning stiffness (MS) of RA patients, and to validate the routine clinically derived duration of MS against that recorded prospectively by patients. Forty-nine RA patients, who during a detailed clinical interview reported experiencing MS that week were studied. They were asked to prospectively record, using a diary, daily information on the duration of their MS. The times both of waking and of getting up were noted, as well as the times to first improvement, maximum improvement and complete disappearance of MS, providing six possible estimates of MS duration, three of which, using waking as starting points, could be compared with the interview. The daily variation of MS was assessed by the within-patient range. The median duration of the diary scores was then compared with the MS estimates recorded at the interview. There was a large intra-individual variation in duration of MS, whichever of the six definitions were used. Half of the patients recorded ranges of MS scores of 3 h or more within the same week. There was also marked variation between the median diary derived duration and that ascertained by interview. This variation was at its smallest when the duration of MS was calculated as time until maximum improvement. The routine recording of the 'typical' duration of MS seems to have little clinical value in the face of the large within-patient variation. Of the possible choices for estimating duration, the time from waking to maximum improvement appeared to be the best indicator of the average duration of MS in RA patients.