Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: It’s all in the Definition

Who has Chronic Fatigue Syndrome? The old school answer is that’s the $64,000 question.  Like many other diseases the cause of chronic fatigue syndrome, also known as myalgic encephalomyelitis, is unknown and there are no biomarkers.

There are however, many different definitions and research shows that they do not select the same set of patients.  Research definitions, by necessity, tend to be shorter because it is unwieldy to account for multiple variables. Clinicians on the other hand can take more factors into account when making a diagnosis.

The most common research definition used in research is a committee definition created under the auspices of the Centers for Disease Control.  Members of the committee included both psychiatrists and biomedical clinicians and researchers with very different viewpoints.  The result was a compromise.

After excluding other diseases/disorders with similar symptoms, the Fukuda research criteria for CFS requires:

A. Six or more months of chronic fatigue of a new or definite onset

B. Four or more of the following eight symptoms:

  • Impaired memory or concentration
  • Tender cervical or ancillary lymph nodes
  • Muscle pain
  • Multi-joint pain
  • New headaches
  • Unrefreshing sleep
  • Post-exertion malaise

According to Dr. Leonard Jason, who has been on several  CFS definition committees  and has published several studies comparing various definition including the Fukuda, one of the main problems with this definition is two patients under the same definition can have no symptoms in common  other than fatigue  lasting six months.  He also states that critical CFS symptoms such as post-exertional malaise, and memory and concentration problems are not required of all patients.

Dr. Vincent Racaniello, a microbiology professor at Columbia University and on the Scientific Advisory Board for the CFIDS Association says multiple definitions complicate things.  “It selects a really heterogeneous group because of the way it is diagnosed at the moment…,” said Dr. Racaniello, “making it hard to find biomarkers.”

Enter the 2003 Canadian Consensus clinical definition. This definition for ME/CFS was developed by a group of clinicians and researchers who collectively had diagnosed and/or treated more than twenty thousand ME/CFS patients. The definition has been used in conjunction with research definitions. Unlike the Fukuda research definition above, the authors of this definition were more specific about the criteria and required specific ME/CFS symptoms to occur.  In other words for example, post exertional fatigue/malaise is not the garden variety tiredness commonly reported in doctor’s offices.

In comparing the Fukuda definition with the Canadian Consensus definition Dr. Jason found that the Canadian ME/CFS criteria selected cases with less psychiatric comorbidity, more physical functional impairment, more fatigue/weakness and more neuropsychiatric and neurological symptoms.

In comparison to the Fukuda definition, the Canadian Consensus Definition has the following criteria for diagnosis:

A patient with ME/CFS will meet the criteria for fatigue, postexertional

Malaise and/or fatigue, sleep dysfunction, and pain; have two or more neurological/cognitive manifestations and one or more symptoms from two of the categories of autonomic, neuroendocrine, and immune manifestations; and adhere to item 7.

  1. Fatigue: The patient must have a significant degree of new onset, unexplained, persistent, or recurrent physical and mental fatigue that substantially reduces activity level.
  2. PostExertionalMalaise and/or Fatigue: There is an inappropriate loss of physical andmental stamina, rapid muscular and cognitive fatigability, post exertional malaise and/or fatigue and/or pain and a tendency for other associated symptoms within the patient’s cluster of symptoms to worsen. There is a pathologically slow recovery period usually 24 hours or longer.
  3. Sleep Dysfunction:* There is unrefreshed sleep or sleep quantity or rhythm disturbances such as reversed or chaotic diurnal sleep rhythms.
  4. Pain:* There is a significant degree of myalgia. Pain can be experienced in the muscles, and/or joints, and is often widespread and migratory in nature. Often there are significant headaches of new type, pattern or severity.
  5. Neurological/Cognitive Manifestations: Two or more of the following difficulties should be present: confusion, impairment of concentration and short-term memory consolidation, disorientation, difficulty with information processing, categorizing and word retrieval, and perceptual and sensory disturbances – e.g. spatial instability and disorientation and inability to focus vision. Ataxia, muscle weakness and fasciculations are common. There may be overload phenomena: cognitive, sensory – e.g. photophobia and hypersensitivity to noise and/ or emotional overload, which may lead to “crash” periods and/or anxiety.
  6. At Least one Symptom from two of the following categories:
    • a. Autonomic Manifestations: orthostatic intolerance neurally mediated hypotension (NMH), postural orthostatic tachycardia syndrome (POTS), delayed postural hypotension; lightheadedness; extreme pallor; nausea and irritable bowel syndrome; urinary frequency and bladder dysfunction; palpitations with or without cardiac arrhythmias; exertional dyspnea.
    • b. Neuroendocrine Manifestations: loss of thermostatic stability – subnormal bodytemperature and marked diurnal fluctuation, sweating episodes, recurrent feelings of feverishness and cold extremities; intolerance of extremes of heat and cold; marked weight change anorexia or abnormal appetite; loss of adaptability and worsening of symptoms with stress.
    • c. Immune Manifestations: tender lymph nodes, recurrent sore throat, recurrent flulike symptoms, general malaise, new sensitivities to food, medications and/or chemicals.

7. The illness persists for at least six months: It usually has a distinct onset, although it may be gradual. Preliminary diagnosis may be possible earlier. Three months is appropriate for children. To be included, the symptoms must have begun or have been significantly altered after the onset of this illness.

In 2011 an International group of ME/CFS researchers /clinicians worked to refine the 2003 Canadian definition and the results were published in the peer-reviewed Journal of Internal Medicine.  First they got rid of the term Chronic Fatigue Syndrome, which has been compared to calling emphysema “chronic cough,”  but retaining Myalgic Encephalomyelitis.  The six month waiting period followed the term CFS.

“No other disease criteria require that diagnoses be withheld until after the patient has suffered with the affliction for six months,” said the authors adding, “Early diagnoses may elicit new insights into the early stages of pathogenesis; prompt treatment may lessen the severity and impact” In a May 2011 interview, Dr. Elizabeth Unger of the Centers for Disease Control agreed the wait makes it more challenging to determine what may have been the trigger for the illness.  Unger also said, “In addition, the chronic nature of CFS makes it likely that additional secondary symptoms will develop. This makes it difficult to determine which features are most closely related to the illness and increases the differences between patients.”

And finally, according to the 2011 International Consensus Criteria primary psychiatric disorders, somatoform disorder and substance abuse are specifically excluded – exclusions that are specifically included in many of the other definitions.

The 2011 research-based criteria remains oriented toward clinical diagnosis with a research definition to follow.

Other definitions exist, but they are rarely or no longer used. Examples include the 1991 so-called Oxford definition which British psychiatrists prefer over any of the international definitions on which they have been authors and the 1988 Holmes criteria. There is a pediatric definition as well modeled on the Canadian Consensus definition.

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