Objective: This study aimed to investigate the independent correlations of subjective sleep disturbances (insomnia and daytime sleepiness) with the severity of fatigue in patients with major depression.
Methods: Eighty-one currently depressed patients (70 females and 11 males), aged between 23 and 65 years, with a DSM-IV diagnosis of major depressive disorder were studied. Patients with physical diseases or other conditions associated with prominent fatigue were excluded. The 17-item Hamilton Depression Rating Scale (HDRS), the Athens Insomnia Scale (AIS), and the Epworth Sleepiness Scale (ESS) were used for the cross-sectional assessment of the severity of depression, insomnia, and sleepiness, respectively. Severity of fatigue was measured with the Fatigue Severity Scale (FSS). Pearson's and Spearman's coefficients were used in bivariate correlations between FSS score and the independent variables (age, gender, inpatient/outpatient status, HDRS score, AIS total score, AIS individual item scores, and ESS score). A stepwise multiple regression analysis was then performed, with FSS score as the dependent variable.
Results: The severity of fatigue was significantly correlated with female sex, HDRS score, AIS total score, awakenings during the night (AIS item 2), compromised sleep quality (AIS item 5), and ESS score. Sleep quality (AIS item 5) and daytime sleepiness (ESS) were the only significant predictors of the severity of fatigue in the multiple regression analysis.
Conclusions: Both sleep quality and daytime sleepiness correlate independently with fatigue severity, as measured with the FSS, in patients with major depression. The FSS does not appear to be a 'pure' measure of fatigue in depressed patients, a finding with potential implications for the choice of appropriate fatigue measures in this population.