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ME/CFS and overlapping illnesses

Dr. Klimas outlined the progress that has been made in properly classifying ME/CFS patients under the very broad 1994 case definition. Researchers have found that there are a variety of illness subgroups under the defini­tion's large umbrella that probably include many patients who do not have ME/CFS.

Dr. Klimas said that the two symptom criteria that are most characteristic of ME/CFS are post­-exertional malaise and unrefreshed sleep. Thus she questions whether a person really has ME/CFS in the absence of these symptoms.

Dr. Klimas next compared ME/CFS and fibromyalgia (FM). While many ME/CFS patients have FM and many FM patients have ME/CFS, there are a "vast majority" of FM patients who do not have ME/CFS. Therefore, while ME/CFS and FM are somewhat overlapping illnesses, they are not the same illness.