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Toward a new definition of chronic fatigue syndrome.

To the editor, 
 
I agree with Lane when he writes that the operative criteria for diagnosing chronic fatigue syndrome (CFS) are unsatisfactory. Some patients who have been assigned this label may be better described as having depression or somatization, and this mislabeling prejudices the understanding of CFS in cross-sectional studies.1 Lane is presumably referring to the definition of the Centers for Disease Control and Prevention, with its concentration on physical symptoms.2 This definition also is not all that helpful in assigning a label to individuals for the purposes of estimating prognosis or deciding on treatment because the physical symptoms cited are nonspecific. 
 
Ideally, the definition of a particular disease should be founded on an understanding of the underlying pathologic mechanism of that disease. On the basis of the studies of Fulcher and White,3 Lane postulates a metabolic myopathy in some patients with CFS (to add to the many other pathologic mechanisms that have been postulated in the past),2 but acknowledges that for many patients with CFS, myopathy may not be an underlying causative factor. At present, the only abnormal physical signs that people with CFS commonly manifest are those related to deconditioning. Until or unless we identify some additional abnormal physical process that is shared by all people with CFS, we need to use a definition based on what else they have in common: their cognition and their behavior. Their cognition includes greater sensitivity to body sensations, an increased importance attributed to these symptoms, and a belief that exercise is harmful and rest is therapeutic. Their behavior reflects that belief. The successful response of most CFS people to cognitive behavior therapy2 supports my contention that this is a useful and adequately accurate definition.