Defining the chronic fatigue syndrome.

The recently published working definition of the chronic fatigue syndrome (CFS) is a necessary first step toward a consistent effort to research this controversial illness. Before this definition was developed, cases often were defined vaguely, according to the perceptions and biases of the individual researchers, so that the results of some studies were unclear. However, few specific diagnostic parameters for CFS exist, and the new definition may not delineate a single clinicopathologic entity. Future efforts at researching this illness should be aimed at identifying parameters that differentiate CFS from psychiatric conditions such as major depression and from other defined chronic diseases. Because CFS may be the result of multiple disease processes, the separate study of well-defined subgroups of patients with CFS is appropriate. Such subgroups of patients are probably more likely to have common pathogenetic features than are patients with CFS as a whole group.