Published in 2003, the Canadian Consensus Criteria (CCC) is a set of diagnostic criteria used for identifying cases of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) for research and clinical purposes. It is also known as the clinical working case definition. In 2010, the CCC was revised to help clinicians and researchers better use the criteria and improve diagnostic reliability, although the core categories remained unchanged.
Summary of the Revised CCC
To be diagnosed with ME/CFS, a patient must meet the criteria for fatigue, post-exertional malaise/fatigue, sleep dysfunction and pain; have 2 or more neurological/cognitive manifestations; and at least 1 symptom from 2 categories of autonomic, neuroendocrine and immune manifestations.
The illness must persist for 6 or more months (3 months is appropriate in children). Thorough history-taking, physical examination and tests are needed to exclude other illnesses.
All of the following must be present:
- Fatigue – Significant physical and mental fatigue that is new onset, unexplained, persistent or recurrent, and substantially reduces activity level;
- Post-exertional malaise and/or post-exertional fatigue – General feeling of discomfort, weakness and/or fatigue, and potentially worsening associated symptoms, following physical or mental exertion; slow recovery which is usually longer than 24 hours;
- Sleep dysfunction* – Unrefreshing sleep or disturbances in sleep quantity or rhythm;
- Pain* – Significant degree of muscle and/or joint pain, and/or significant headaches of new type, pattern or severity.
2 or more of the following neurological/cognitive manifestations must be present:
- Impairment of concentration and short-term memory consolidation;
- Perceptual and sensory disturbances; e.g. spatial instability and disorientation, and inability to focus vision;
- Difficulty with information processing, categorising and word retrieval;
- Motor disturbances: ataxia, muscle weakness and fasciculations, loss of balance and clumsiness commonly occur;
- Overload phenomena: cognitive, sensory (e.g. hypersensitivity to noise and light), emotional overload which may lead to crash (temporary immobilising physical and/or mental fatigue) and/or anxiety.
At least 1 symptom from 2 of the following categories must be present:
- Autonomic manifestations
- Orthostatic intolerance (neurally mediated hypotension (NMH), postural orthostatic intolerance (POTS), delayed postural hypotension);
- Palpitations (with or without cardiac arrythmias);
- Extreme pallor;
- Shortness of breath on exercise;
- Nausea and irritable bowel syndrome;
- Urinary frequency and bladder dysfunction.
- Neuroendocrine manifestations
- Loss of thermostatic stability (temperature does not remain stable);
- Intolerances of extremes of heat and cold;
- Recurrent feelings of feverishness and cold extremities;
- Marked weight change (anorexia or abnormal appetite);
- Loss of adaptability and worsening symptoms with stress.
- Immune manifestations
- Tender lymph nodes;
- Recurrent sore throat;
- Recurrent flu-like symptoms;
- General malaise (flu-like feelings of being ill and feverish);
- New sensitivities to food, medications and/or chemicals.
*There is a small number of patients without pain or sleep dysfunction, but no other diagnosis fits except ME/CFS. A diagnosis of ME/CFS can be considered in these cases if the illness has an infectious onset.
Unlike previously published criteria, the CCC and revised CCC require the presence of post-exertional malaise (PEM), which is now considered a cardinal feature of ME/CFS. Nevertheless, as with other criteria, there are certain factors to consider:
- Evaluation of extensive symptoms: Clinicians may need to evaluate a significant number of symptoms, prior to diagnosing ME/CFS, which could be challenging from a practical standpoint.
- Exclusion from diagnosis: Likely due to the greater symptom requirements, the CCC and revised CCC exclude more people from a diagnosis than the Fukuda criteria. On one hand, the increased specificity (ability to accurately identify individuals with a condition) enhances the homogeneity (alikeness) of study populations and potentially increases the accuracy of results. On the other hand, the broader inclusivity of the Fukuda criteria could capture a wider spectrum of the condition. Note: Due to their differences, it is difficult to compare the findings of a study utilising the CCC and revised CCC to a study utilising Fukuda criteria.
- Palpitations and cardiac arrythmias: The presence of palpitations with a cardiac arrythmia (abnormal heart rhythm) could contribute to a diagnosis of ME/CFS, rather than pointing to a comorbid condition. Whilst the criteria mention a 24-hour Holter (used for monitoring heart activity) may be indicated, it is crucial to emphasise the importance of excluding other causes of cardiac arrythmias.
- Carruthers BM, et al. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Journal of Chronic Fatigue Syndrome, 2003; 11(1):7–115. Available at: doi.org/10.1300/j092v11n01_02
- Jason. The Development of a Revised Canadian Myalgic Encephalomyelitis Chronic Fatigue Syndrome Case Definition” American Journal of Biochemistry and Biotechnology, 2010; 6(2):120–35. Available at: doi.org/10.3844/ajbbsp.2010.120.135
- Committee on the Diagnostic Criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome; Board on the Health of Select Populations; Institute of Medicine. Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. Washington (DC): National Academies Press (US); 2015 Feb 10. 3, Current Case Definitions and Diagnostic Criteria, Terminology, and Symptom Constructs and Clusters. Available from: ncbi.nlm.nih.gov/books/NBK284898/#