Circadian rhythm in pain, stiffness, and manual dexterity in rheumatoid arthritis: relation between discomfort and disability.

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Abstract
Fourteen patients with rheumatoid arthritis (RA) self rated their pain and stiffness on separate 10 cm visual analogue scales and performed bead intubation coordinometry (BIC) on six occasions each day for seven consecutive days. In addition, 14 healthy controls matched for age and sex also performed BIC measurements according to the same schedule. Data were analysed using least squares and cosine vector techniques. Significant circadian rhythms in patients with RA were detected in pain, stiffness, and BIC, and in controls in BIC. Pain was least in patients with RA at 1700 and stiffness at 1724. Peak BIC performance occurred almost simultaneously in RA (1544) and control (1528) subjects and for subjects with RA occurred within the 95% confidence interval of least pain and stiffness. These data suggest that the inferior performance of subjects with RA may be an accentuation of the normal physiological variation seen in healthy controls, but may be modulated by the patient's level of pain or stiffness, or both.