Aspects of diurnal rhythmicity in pain, stiffness, and fatigue in patients with fibromyalgia

Objective. To determine diurnal rhythm characteristics of pain, stiffness, and fatigue in self-ratings performed by patients with fibromyalgia (FM). Methods. Twenty-one women with FM made self-measurements of pain, stiffness, and fatigue on 100 nun horizontal visual analog scales at 6 prespecified timepoints at home for 10 consecutive days. Linear and multiple regressions were performed on the original data and the 24-hour means vs FM classifiers (age, disease duration, tender points, dolorimetry score, Fibromyalgia Impact Questionnaire score), respectively. Data were analyzed for 24-hour and 7-day time-effects by ANOVA and for diurnal and weekly rhythms by the cosinor technique. Results. Individual ratings for pain, stiffness, and fatigue correlated highly with each other throughout the day and over the days of the week. Of the FM classifiers, dolorimetry score was found to be inversely related to the pain, stiffness, and fatigue scores. For the group of subjects with a low dolorimetry score (< 2.25 kg), a significant diurnal rhythm was found in each self-rated variable, with greater pain, stiffness, and fatigue observed in the morning and least in the late afternoon. No rhythm in pain or stiffness was observed in those subjects with a higher threshold for pain (dolorimetry score > 2.25 kg), while fatigue showed the same significant diurnal pattern as in the first group. For the group as a whole, the possible presence of a weekly variation was found with ratings for pain, stiffness, and fatigue higher on Sunday and Monday and lower on Friday. Conclusion. Ratings of pain, stiffness, and fatigue in FM are significantly correlated, and show diurnal and possibly weekly rhythmicity, especially when pain threshold is low (dolorimetry score < 2.25 kg), and are thus predictive of each other over these time spans. This has important implications for scheduling activities of daily living, for measurement in clinical trials, and possibly for timing the administration of medications.