Distinguishing fatigue and depression in patients with cancer.

In seeking to learn more about the etiology and treatment of fatigue in patients with cancer, clinicians and researchers have been challenged to understand how fatigue can be distinguished from depression. Approaches currently used to study fatigue and depression in patients with cancer appear to be of limited usefulness in distinguishing these phenomena. This conclusion is supported by a review of studies in which the single-symptom and symptom-cluster approaches were used to measure fatigue and depression concurrently in patients with cancer. The review yielded consistent evidence of high positive correlations between fatigue and depression, even when attempts were made to eliminate overlapping item content. A consideration of causal mechanisms suggests why it remains difficult to distinguish between fatigue and depression. In addition to fatigue being a possible cause of depression and depression being a possible cause of fatigue, both fatigue and depression can share a common cause. That is, certain forms of cancer and cancer treatment can cause both fatigue and depression. These different mechanisms have implications for efforts to distinguish fatigue and depression and to identify appropriate treatments. For example, recently developed diagnostic criteria for a clinical syndrome of cancer-related fatigue might be useful in identifying fatigue that is caused by a major depressive disorder for which antidepressant therapy is generally indicated.