The development of a practical case definition for the chronic fatigue syndrome has been extremely difficult because of the protean symptoms of the disorder and the lack of a specific diagnostic test or pathognomonic sign. In the absence of such a gold standard for defining the disorder, Fukuda and the International Chronic Fatigue Study Group (at the Centers for Disease Control and Prevention) [1] have proposed a case definition for the syndrome. The authors state, however, that this definition is specifically designed for research purposes only, leaving practitioners and others without a satisfactory diagnostic tool.

We present in Table 1 a case definition for practitioners that is modeled after the CDC case definition and that is so similar that the reader is referred to Fukuda and colleagues' paper [1] for details and an excellent discussion. The case definition for practitioners entails a step-by-step approach to exclude other causes of fatigue and defines the case in terms of two cardinal symptoms (severe fatigue and neurocognitive dysfunction) and at least four of eight minor signs and symptoms. Unlike the research criteria, therefore, neurocognitive dysfunction has been elevated to the major criteria, and minor criteria are more descriptive. We have also included special characteristics (type of onset and severity of illness) that we believe may subcategorize the patient population.

The practicing physician may use this case definition as a "bedside guide" by simply checking off each step as the requirements have been met. If all the steps have been met, then the practitioner may select "patient meets criteria for chronic fatigue syndrome" under the final clinical impression.

We hope that practitioners will find this case definition both fitting and easy to use, thereby providing a suitable tool for diagnostic as well as medical-legal and insurance purposes.