Canadian ME/CFS Clinical Case Definition -
An important medical milestone
Published in 2003, this clinical diagnostic criteria for myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) was developed by an expert medical consensus panel of working physicians, teaching faculty and world leaders in the research of ME/CFS.
The expert panel of 11 physicians-who have diagnosed and/or treated more than 20,000 ME/CFS patients between them-has developed a clinical case definition that provides a flexible conceptual framework based on the characteristic patterns of symptom clusters, which reflect specific areas of pathogenesis. The definition reflects the complexity of symptoms of a given patient's pathogenesis and should establish ME/CFS as a distinct medical entity and help distinguish it from overlapping medical conditions in the absence of a definitive laboratory test.
"The clinical definition will enable clinicians to make an early diagnosis which may assist in lessening the impact of ME/CFS in some patients," said Dr. Bruce M. Carruthers, lead author of the definition. "It will reduce the expensive problem of patients being sent to many specialists before being diagnosed and will allow patients to receive appropriate treatments in a timely fashion."
The panel's clinical case definition determines that more of the prominent symptoms are compulsory for the diagnosis and symptoms that share a common region of pathogenesis are grouped together for clarity.
The clinical working case definition states that a patient with ME/CFS will meet the criteria for fatigue, post-exertional 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.
- Severe prolonged fatigue
The patient must have a significant degree of new onset, unexplained, persistent, or recurrent physical and mental fatigue that substantially reduces activity level.
- Post-exertional malaise and/or fatigue
There is an inappropriate loss of physical and mental 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.
- Sleep dysfunction
There is unrefreshed sleep or sleep quantity or rhythm disturbances such as reversed or chaotic diurnal sleep rhythms.
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.
- 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.
- 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; light-headedness; 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 body temperature 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 flu-like symptoms, general malaise, new sensitivities to food, medications and/or chemicals.
- 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. It is unlikely that a patient will suffer from all symptoms in criteria 5 and 6. The disturbances tend to form symptom clusters that may fluctuate and change over time. Children often have numerous prominent symptoms but their order of severity tends to vary from day to day.
There is a small number of patients who have no pain or sleep dysfunction, but in whom no other diagnosis fits except ME/CFS. A diagnosis of ME/CFS can be entertained when this group has an infectious illness type onset.
Some patients have been unhealthy for other reasons prior to the onset of ME/CFS and lack detectable triggers at onset and/or have more gradual or insidious onset.
Exclusions: Exclude active disease processes that explain most of the major symptoms of fatigue, sleep disturbance, pain, and cognitive dysfunction. It is essential to exclude certain diseases, which would be tragic to miss: Addison's disease, Cushing's Syndrome, hypothyroidism, hyperthyroidism, iron deficiency, other treatable forms of anaemia, iron overload syndrome, diabetes mellitus, and cancer. It is also essential to exclude treatable sleep disorders such as upper airway resistance syndrome and obstructive or central sleep apnoea; rheumatological disorders such as rheumatoid arthritis, lupus, polymyositis and polymyalgia rheumatica; immune disorders such as AIDS; neurological disorders such as multiple sclerosis (MS), Parkinsonism, myasthenia gravis and B12 deficiency; infectious diseases such as tuberculosis, chronic hepatitis, Lyme disease, etc.; primary psychiatric disorders and substance abuse. Exclusion of other diagnoses, which cannot be reasonably excluded by the patient's history and physical examination, is achieved by laboratory testing and imaging. If a potentially confounding medical condition is under control, then the diagnosis of ME/CFS can be entertained if patients meet the criteria otherwise.