by Sasha Nimmo

Norwegian researchers asked ‘What exactly is myalgic encephalomyelitis?’ and found it is not the same as chronic fatigue syndrome. Broad criteria results in misdiagnosis and incorrect treatment. Researchers need narrower criteria to develop effective treatments.

Myalgic encephalomyelitis is a “reasonably well-defined disorder with distinct clinical characteristics”, according to research published in October 2015, which reviewed the major clinical definitions.

“Patients with myalgic encephalomyelitis have more severe symptomatology than those with chronic fatigue syndrome, but better mental health…we believe that it is important to distinguish between myalgic encephalomyelitis and chronic fatigue syndrome.  Many studies have included very heterogeneous patient populations, where perhaps only a minority of individuals had what we would define as myalgic encephalomyelitis.”

The authors recommend a “more deliberate use of the diagnostic criteria” to improve understanding of the disease, treatment and patients’ lives. They also believe it will lay foundations for ramping up biomedical research.

They warn that “use of broad inclusion criteria has created a heterogeneous patient population… This has increased the risk of erroneous conclusions, misdiagnosis and incorrect treatment”.   Stating the lack of success of the PACE trial, “it is unfortunate that psychosomatic therapy continues to be recommended by the health authorities”.

Better defining patient cohorts will lead to more useful research they say, but point out Norway’s Directorate of Health confusingly recommend either the Fukuda or Canadian criteria, which have many differences between them.

Agreeing with other recent research, they state ME “may consist of several subtypes, which cannot at present be distinguished using existing diagnostic criteria. Such subtypes may have distinct aetiologies and pathogenic mechanisms, which could require different therapeutic approaches.” The paper mentioned Rituximab, “the antibody treatment against B lymphocytes had beneficial effects in a majority of patients”.

They point out a recent USA NIH report “concludes that continued use of the Oxford criteria (the broadest) may impair progress and cause harm, and recommends that these criteria should no longer be used.”

Not in this paper, but it is interesting to note agreement with other scientists: At the 2015 Sweden Seminar on Essential Features of ME and CFS, Dr Leonard Jason of DePaul University (Chicago, USA) was asked about the SEID criteria (40 minutes into the video). Dr Jason said only 20 per cent of those meeting SEID criteria would meet Fukuda, due to medical and psychiatric exclusions, and that there are many different types on illness within that criteria. Comparing patients who meet the SEID criteria to those who meet the Canadian Consensus Criteria, the Canadian is the more impaired group. For researchers, the aim is to have patients as comparable as possible, however for clinical purposes, the IOM are easier to use but Dr Jason expresses concern it should not be used as research criteria.

The Norwegian paper (in English) is well worth reading for the summary of criteria alone:

Oxford criteria for chronic fatigue syndrome (1991)

Drafted by an English group consisting largely of psychiatrists (27). The main criterion is severe fatigue for at least six months. Other diseases must be excluded. The Oxford criteria are very broad, but are still used to some degree in research. Neither the Norwegian Directorate of Health nor the US health authorities recommend use of these criteria today.

Fukuda criteria for chronic fatigue syndrome (1994)

Drafted by the Centers for Disease Control and Prevention (CDC) on the basis of Fukuda et al. (28). In addition to severe fatigue for at least six months, and the exclusion of other diseases, at least four of eight defined symptoms must be present: impaired short-term memory and/or concentration, sore throat, tender lymph nodes, muscle pain, joint pain, new-onset headache, unrefreshing sleep, and post-exertional malaise. These criteria have been central to research.

Canadian criteria for myalgic encephalomyelitis/chronic fatigue syndrome (2003)

Drafted by doctors and researchers and represent a refinement and narrowing of the Fukuda criteria (6). The Canadian criteria require the patient to have six different symptoms: severe physical and mental fatigue, post-exertional malaise or fatigue, sleep dysfunction, pain in muscles, joints and the head, neurological/cognitive features (minimum of two symptoms, e.g. confusion, impaired concentration, ataxia), and autonomic, e.g. nausea and irritable bowel, neuroendocrine, e.g. loss of thermostatic stability, or immune disorders.

International consensus criteria for myalgic encephalomyelitis (2011)

Drafted by an international panel of experts from 13 countries (4) and a refinement of the Canadian criteria. A diagnosis of myalgic encephalomyelitis requires the patient to fulfil criteria within four categories: (a) post-exertional neuroimmune exhaustion, often with significantly prolonged recovery period, (b) neurological impairments, i.e. symptoms from three of four categories: cognitive abilities, pain, sleep disturbances and/or neurosensory, perceptual or motor disturbances, (c) immune, gastrointestinal and genitourinary impairments from three of five categories, including flu-like symptoms, nausea and hypersensitivity, and (d) impairments of energy production and energy transport within one of four categories: cardiovascular, respiratory, thermoregulatory and/or intolerance of extreme temperatures. The criteria have also been adapted for paediatric populations.

Paediatric criteria for myalgic encephalomyelitis and chronic fatigue syndrome (2006)

Various paediatric diagnostic criteria have been used. The Norwegian Directorate of Health recommends the criteria presented by Jason et al. (29), which require chronic fatigue for at least three months and exclusion of other diseases. Additional requirements include post-exertional malaise/fatigue, unrefreshing sleep or other sleep disturbances, pain in muscles, joints, stomach or head, neurocognitive features, at least 2 of 12, and at least one symptom within the three groups autonomic, neuroendocrine and immune. Severe psychiatric disorders that could explain the chronic fatigue, such as anorexia and bulimia, are exclusionary.

Systemic Exertion Intolerance Disease (SEID) criteria (2015)

Proposed by the Institute of Medicine in the United States (5). The diagnosis requires a significant loss of functional capacity, post-exertional malaise (PEM) and sleep disturbances (unrefreshing sleep). Additional criteria are also proposed, including cognitive impairment and/or orthostatic intolerance. The proposers suggest that the term myalgic encephalomyelitis should be replaced with «Systemic Exertion Intolerance Disease» (SEID).

The full paper in English.