Pain, sleep disturbance, and fatigue in patients with cancer: using a mediation model to test a symptom cluster.

PURPOSE/OBJECTIVES To test whether sleep disturbance mediates the effect of pain on fatigue. DESIGN Cross-sectional. SETTING Radiation therapy clinic, oncology ambulatory clinic, and inpatient oncology unit in an urban teaching hospital. SAMPLE 84 patients with cancer with multiple primary diagnoses who were experiencing pain. Fifty-three percent were female and 92% were Caucasian, with a mean age of 54 years. METHODS All participants completed a symptom questionnaire that included the Brief Pain Inventory-Short Form, the Pittsburgh Sleep Quality Index, and the fatigue subscale of the Profile of Mood States questionnaire. Multistage linear regression was used to test a mediation model. MAIN RESEARCH VARIABLES Fatigue, pain, and sleep disturbance. FINDINGS Mediation analyses indicate that pain influences fatigue directly as well as indirectly by its effect on sleep. About 20% (adjusted R2 = 0.20) of the variation in fatigue is explained by pain. Thirty-five percent of the variance in fatigue explained by pain was accounted for by the mediation pathway. CONCLUSIONS Some of the effect of pain on fatigue is mediated by sleep disturbance, but pain has a direct effect on fatigue as well. IMPLICATIONS FOR NURSING Although the relationship can be explained only partially by the commonsense point of view that people who are in pain lose sleep and naturally report more fatigue, this finding is important and leads to a potential intervention opportunity. Strategies to improve sleep by better pain management may contribute to decreased fatigue.