Required Canadian Diagnostic Criteria for ME/CFS (in summary)

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

1. "the criteria for fatigue, post-exertional malaise and/or fatigue, sleep dysfunction, and pain" explained below
2. "have two or more neurological/cognitive manifestations"
3. "one or more symptoms from the categories of autonomic, neuroendocrine and immune manifestations"
4. "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."

The definition also makes clear that the symptom criteria cannot be used as a mere template for diagnosis, but must be applied according to stated guidelines (to be summarized shortly.)

Thus, to be diagnosed the person must qualify under each and all of the following symptom categories (as qualified in the further application categories):

1. "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."
2. "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."
3. Sleep dysfunction: There is non-restorative sleep or decline in sleep quantity or dysregulation of normal sleep rhythms.
4. 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".
5. "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; and b) more classical neurological symptoms, including difficulty walking and muscle weakness; sensory hypersensitivity, including lower threshold for emotional overload.
6. 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."