Diurnal courses of cortisol, pain, fatigue, negative mood, and stiffness in patients with recently diagnosed rheumatoid arthritis

To investigate the diurnal courses of cortisol and the daytime states: pain, fatigue, negative mood, and stiffness of patients with rheumatoid arthritis, as well as the association between the cortisol and state courses, 9 repeated measurementson 2consecutive days were taken in the real-life environment of 25 recently diagnosed patients (19 women, 6 men; mean age 55.2 years) and 28 healthy controls (20 women, 8 men; mean age 55.8 years). Patients showed a highly characteristic diurnal course of cortisol (F_{8, 15} = 7.4, p < .001) and a significant diurnal fatigue (F_{7, 18} = 2.6, p < .05) and early morning stiffness course (F3, 22 = 6.2, p < .01), but the temporal association between these courses was low. Daytime states, notably fatigue (r = 0.40, p < .05), were positively correlated with the early morning rise of cortisol and nighttime pain (r ≥ 0.53, p < .01) but not with cortisol level or inflammatory activity. Cortisol level and inflammatory activity were positively correlated (r = 0.47, p < .05). These results suggest that in patients with rheumatoid arthritis, cortisol has a strong endogenous rhythm that is not disturbed by inflammatory activity. It appears that diurnal fluctuations in fatigue and stiffness are independent of the circadian rhythm of cortisol or inflammatory activity, but rather reflect temporal changes as a consequence of sleep, rest, and physical activity throughout the day.