This case definition was authored by a group of international CFS experts, convened by the U.S. Centers for Disease Control & Prevention (CDC) in 1994, to update and refine an earlier (1988) case definition. Its purpose was to provide standard criteria for researchers who were investigating the illness.

Even though the criteria were developed for use in research, medical practitioners use it as a diagnostic guideline in their clinical practice. In 2003, the CDC revised the criteria in an attempt to clarify ambiguities in the 1994 definition. A clinical case definition has not yet been developed in the U.S.

The Chronic Fatigue Syndrome:
A Comprehensive Approach to its Definition and Study

Keiji Fukuda, M.D., M.P.H., Stephen E. Straus, M.D., Ian Hickie, M.D., F.R.A.N.Z.C.P., Michael C. Sharpe, M.R.C.P., M.R.C. Psych., James G. Dobbins, Ph.D., Anthony L. Komaroff, M.D., F.A.C.P. and the International Chronic Fatigue Syndrome Study Group 

From the Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia; Laboratory of Clinical Investigation and Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland; School of Psychiatry, Prince Henry Hospital, University of New South Wales, Sydney, Australia; University of Oxford Department of Psychiatry, Warneford Hospital, Oxford, United Kingdom; and Division of General Medicine, Brigham and Women's Hospital, Harvard University, Boston, Massachusetts.

Abstract

The complexities of the chronic fatigue syndrome and the methodologic problems associated with its study indicate the need for a comprehensive, systematic, and integrated approach to the evaluation, classification, and study of persons with this condition and other fatiguing illnesses. We propose a conceptual framework and a set of guidelines that provide such an approach. Our guidelines include recommendations for the clinical evaluation of fatigued persons, a revised case definition of the chronic fatigue syndrome, and a strategy for subgrouping fatigued persons in formal investigations. We have developed a conceptual framework and a set of research guidelines to use in studies of the chronic fatigue syndrome. The guidelines cover the clinical and laboratory evaluation of persons with unexplained fatigue; the identification of underlying conditions that may explain the presence of chronic fatigue; revised criteria for defining cases of the chronic fatigue syndrome; and a strategy for subdividing the chronic fatigue syndrome and other unexplained cases of chronic fatigue into subgroups.

Complete text of the Revised Case Definition is available through the Annals of Internal Medicine

Fukuda et al, Annals of Internal Medicine, Vol. 121, December 15, 1994, pp. 953-959.