The Fukuda et al. (1994) case definition for chronic fatigue syndrome (CFS) requires an individual to experience six or more months of chronic fatigue of a new or definite onset that is not substantially alleviated by rest, not the result of ongoing exertion, and results in substantial reductions in occupational, social, and personal activities. The Fukuda et al. case definition uses a polythetic approach for assessing symptomatology. This type of approach means that not all definitional symptoms need to be present for a diagnosis to be made. Because the Fukuda et al. criteria only require four symptoms out of a possible eight, critical CFS symptoms such as post-exertional malaise, and memory and concentration problems are not required of all patients. The Fukuda criteria, with updates made by Reeves et al. (2003), remain the most universally utilized criteria to date for research and clinical purposes.
The term Myalgic Encephalomyelitis (ME) was used prior to the term CFS (Acheson, 1959). ME was first described in literature of the 1930s, where an outbreak of Epidemic Neuromysthenia in L.A. County was called "atypical poliomyelitis" because of its resemblance to polio (Gilliam, 1938; Hyde, 2007). In 1956, an anonymous editorial in an issue of the Lancet coined the term benign Myalgic Encephalomyelitis (Anonymous Editorial, 1956). It was called 'benign' because the illness did not lead to patient death. Later, Ramsay (1988) published a case definition for this disease using the term Myalgic Encephalomyelitis (ME) and the term benign was dropped due to the seriousness of the disability created by the illness (Hyde, Goldstein, & Levine, 1992). Jason, Damrongvachiraphan et al. (2012) recently developed a consensus ME case definition influenced by some of the key ME theorists over the past few decades (Dowsett et al., 1990; Goudsmit et al., 2009; Hyde, 2007; Ramsay, 1988). The resulting case definition requires an individual to experience post-exertional malaise, at least one neurological symptom, and at least one autonomic symptom. Furthermore, the onset of the condition had to have been sudden (developing over one week or less). Jason, Brown, et al. (2012) found that a sample of individuals meeting these ME criteria and the Fukuda et al. criteria were more impaired and symptomatic than a sample of individuals who only met the Fukuda et al. criteria.
In 2003, a clinical case definition was developed using the term ME/CFS (Carruthers et al.). These criteria became known as the 2003 Clinical Canadian ME/CFS case definition (CCC), and unlike the polythetic approach of the Fukuda et al. (1994) criteria, they required the occurrence of specific ME/CFS symptoms. For example, these criteria specified that post-exertional malaise must occur with a loss of physical or mental stamina, rapid muscle or cognitive fatigability, usually taking 24 hours or longer to recover. These criteria also required the presence of neurocognitive dysfunction. To meet the criteria, a person must also experience at least one symptom indicating sleep dysfunction, at least one symptom indicating significant bodily pain, and at least one symptom from two of the following categories: autonomic manifestations, neuroendocrine manifestations, and immune manifestations. Additionally, this symptom complex must result in substantial reduction of an individual's functioning. As these criteria require specific symptoms, they may select for a more homogenous group of individuals than the polythetic approach of the Fukuda et al. (1994) case definitions. However, the CCC lack operationalization, with no guidelines provided regarding frequency or severity of required symptoms (Jason, Evans, Porter et al., 2010). Therefore, although the CCC may identify a more homogenous sample with regards to what symptoms are occurring, the intensity of these symptoms could range significantly.
Jason and colleagues (2004) compared persons meeting the 2003 Clinical Canadian case definition (Carruthers et al. …