What's in a Name? Word descriptors of cancer-related fatigue

Many different words are used to describe fatigue. It is unclear whether these word descriptors represent the same cancer symptom or dimension. The objective of this study was to identify clinical associations of three fatigue word descriptors (FWDs): 'easy fatigue', 'weakness', and 'lack of energy' (LOE). One thousand consecutive palliative medicine patients completed a 38-item symptom checklist. The prevalence of the three FWDs alone and in combination was calculated. Spearman correlations assessed associations between FWDs. Logistic regression analysis identified univariable and multivariable predictors for each FWD. Survival was estimated using the Kaplan-Meier method, individually and for 0-1 versus 2-3 FWDs, and compared using log-rank tests. The prevalence of easy fatigue was 69%, weakness 66%, and LOE 61%. Correlations between the FWDs were high (0.65-0.79). In multivariable models, clinical associations (particularly neuro-psychiatric symptoms and performance status) of the FWDs were variable. Weakness was associated with performance status, but not anxiety or depression. LOE was associated with anxiety and depression, but not performance status. Fatigue was associated with depression, but not anxiety or performance status. All FWDs were associated with dry mouth, early satiety, sleep problems, and weight loss. The worst survival was associated with two or three reported FWDs compared with none or one (P < 0.001). Weakness and LOE had distinct clinical associations that differed from fatigue. Evaluation of fatigue should use multiple descriptors (particularly weakness), as they are not synonymous. Further research is necessary to identify biological associations for discrete FWDs.