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The lack of clarity and accuracy of the dominant, but somewhat amorphous 1994 Centers for Disease Control & Prevention (CDC) definition for the Chronic Fatigue Syndrome (CFS) led a number of the leading researchers and clinicians from the U.S. and other nations to develop and publish in 2003 a new and much more accurate case definition/diagnostic criteria for the illness:

"Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Definition, Diagnostic and Treatment Protocols"

As this definition was published partially under the auspices of the Canadian Ministry of Health, it is informally called the Canadian Definition. The Canadian government assisted in organizing a committee following "input from invited world leaders in the research and clinical management of ME/CFS patients." (The combined experience of the committee was with over 20,000 patients.)

The Canadian Definition and Diagnostic protocols draw together the most rigorous findings both from the CFS-CDC sponsored research and the ME European research. Authors include CFS/ME experts Dr. Kenny De Meirleir of Belgium and Drs. Martin Lerner, Daniel Peterson, and Nancy Klimas of the U.S., among others.

To date, in our opinion the Canadian Definition is the most medically accurate and detailed case definition for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) available to physicians and patients. A patient and his/her physician will best determine presence of the illness using the Canadian Diagnostic Criteria.

If necessary, a patient can print out the Canadian Definition and take it to his or her physician.