Circadian variation in disease activity in rheumatoid arthritis.

Disease activity in rheumatoid arthritis as measured by repeated estimation of joint pain, stiffness, articular index, and grip strength was shown to have a circadian rythm, maximal activity being seen between 0200 and 0400 and minimal activity in the early afternoon. This variation in disease activity may be related to circadian alterations in immune and inflammatory responses (such as immune complexes and neutrophil function) dependent on alterations in circulating concentrations of steroids. The circadian variation in disease activity has important implications in assessment of patients, prescription of drugs, and performance of drug trials.