[Definition of "chronic fatigue syndrome" (CFS)].

The definition of "Chronic Fatigue Syndrome" (CFS) in 1988 was an attempt to establish a uniform basis for the previously heterogeneous approaches to research of this severe and inexplicable state of fatigue. At the same time, researchers wished to narrow down a pathogenetically founded disease entity a priori by specifying precise disease criteria. The empirical data gathered in accordance with the CFS definition, however, have failed to confirm the assumption that the disease entity is pathogenetically uniform. Furthermore, the originally selected criteria have proven to be impracticable ore theoretically questionable. In the period that followed, modifications that permitted a more comprehensive and yet more differentiated classification of fatigue states of unclear etiology were proposed. The new research approach avoids postulation of causal entities and puts CFS back in a category with other descriptive states of fatigue.