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Diagnostic criteria for ME/CFS

What is Necessary to Receive a Correct and Accurate Diagnosis of An Illness?

Before any illness can be diagnosed, medical science must provide an accurate "case definition" for the illness—a definition that correctly describes the signs, symptoms, illness progression, pathophysiology (deleterious effects of the illness on the body), laboratory abnormalities, and known causal agents. Second, this "case definition" must distinguish the specific illness from other known illnesses—otherwise a specific illness would not be distinguishable from other illnesses, and a diagnosis of it would be impossible.

The preceding discussion is necessary because there has been much confusion and disagreement as to what the illness ME/CFS actually is. Not only is the illness known by various names, but there are several different case definitions that describe the illness somewhat differently and provide different diagnostic criteria. Because the illness first became widely identified in the mid-1980s, a number of case definitions and diagnostic criteria were developed as physicians and researchers learned more about the illness.

Because it is a syndrome and thus only diagnosed by a collection of signs and symptoms in a case definition, receiving an accurate diagnosis of ME/CFS can be difficult. A diagnosis must be obtained from a physician who is knowledgeable about the illness, knows how to rule out other illnesses that can cause similar symptoms, and can apply a case definition accurately.

In early 2015, the United States Institute of Medicine proposed another new diagnostic criteria for ME/CFS. As yet this criteria is a proposal and has not been adopted by the Federal Health Agencies, clinical physicians, and researchers. They also proposed a new name, Systemic Exertional Intolerance Disease (SEID). So far this name has not been adopted by anyone else.

As of late 2015, there are two principal diagnostic criteria used to diagnosis ME/CFS: the 2003 Canadian Definition and the 1994 Centers for Disease Control definition. In our view and that of many ME/CFS experts, the Canadian Definition is superior in accurately diagnosing the illness.

Unfortunately, the 2003 Canadian definition of ME/CFS is complex. We will give a summary below. For more detail, see the article 2003 Canadian definition and pp. 43-44 of the ME/CFS: A Primer for Clinical Practitioners. All quotations below are from the original medical paper.1


2003 Canadian case definition of ME/CFS

The definition first requires that other illnesses which could explain a patient's symptoms be ruled out.

To have ME/CFS, a patient must meet all four of these criteria:

  • "the criteria for fatigue, post-exertional malaise and/or fatigue, sleep dysfunction, and pain" explained below
  • "have two or more neurological/cognitive manifestations"
  • "one or more symptoms from the categories of autonomic, neuroendocrine and immune manifestations"
  • "the illness persists for at least six months usually having a distinct onset, although it may be gradual." A "preliminary diagnosis may be possible earlier."

Thus, to be diagnosed the person must qualify under each and all of the following symptom categories:

  • "Fatigue: The patient must have a significant degree of new onset, unexplained, persistent, or recurrent physical and mental fatigue that reduces activity level. Three months is appropriate for children."
  • "Post-exertional malaise...There is an inappropriate loss of physical and mental stamina, rapid muscular and cognitive fatigability, post-exertional malaise...and/or pain and a tendency of other associated symptoms within the patient's cluster of symptoms to worsen. There is a pathologically slow recovery period—usually 24 hours or longer."
  • Sleep dysfunction: There is non-restorative sleep or decline in sleep quantity or dysregulation of normal sleep rhythms.
  • Pain. "There is a significant degree of myalgia." The word means muscle pain, and is often the type of deep muscle pain experienced during the flu. "Pain can be experienced in the muscles/joints, and is often widespread and migratory in nature." There are often headaches of a "new type, pattern or severity."
  • "Neurological/Cognitive Manifestations"—To qualify in this category two or more of the listed symptoms must be present. Please see the specific list of symptoms in the actual document. They are grouped into:

    a) cognitive deficits including problems with memory, information processing, difficulties with thinking, and perceptual disturbances

    b) more classical neurological symptoms, including difficulty walking and muscle weakness; sensory hypersensitivity, including lower threshold for emotional overload.

  • "Autonomic, Neuroendocrine and Immune Manifestations"—To qualify under this category the patient must have at least one symptom from two of the following three subcategories. Often a patient will have multiple symptoms:

    a) "Autonomic Manifestations: orthostatic intolerance, neurally-mediated hypotension; postural orthostatic tachycardia; light-headedness; extreme pallor; nausea and irritable bowel syndrome; urinary frequency and bladder dysfunction; difficulty breathing upon exertion; palpitations with or without cardiac arrhythmias."

    b) "Neuroendocrine Manifestations: loss of thermostatic stability—subnormal body temperature...sweating episodes, recurrent feelings of feverishness and cold extremities; intolerance of heat and cold, marked weight change—anorexia or abnormal appetite; loss of adaptability and worsening symptoms with stress."

    c) "Immune Manifestations: tender lymph nodes, recurrent sore throats, recurrent flu-like symptoms, general malaise, new sensitivities to food, medications and or chemicals


1. Carruthers et al. "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Definition, Diagnostic and Treatment Protocols," Journal of Chronic Fatigue Syndrome 11, No. 1 (2003): 18-126.