Canadian Consensus Criteria (2003)
The Canadian Consensus Criteria (Carruthers et al. 2003) emerged from a panel of physicians, researchers, and teaching faculty to provide a clinically oriented case definition emphasizing characteristic features.
1 Required Criteria
Diagnosis requires ALL of the following:
1. Fatigue
- Clinically evaluated, unexplained persistent or relapsing chronic fatigue
- New or definite onset (not lifelong)
- Not result of ongoing exertion
- Not substantially alleviated by rest
- Substantial reduction in previous levels of occupational, educational, social, or personal activities
2. Post-Exertional Malaise and/or Fatigue (MANDATORY)
- Inappropriate loss of physical and mental stamina
- Rapid muscular and cognitive fatigability
- Post-exertional malaise and/or fatigue
- Tendency for other associated symptoms within the patient’s cluster to worsen
- Recovery period: Pathologically slow (24 hours or longer)
3. Sleep Dysfunction
- Unrefreshing sleep or sleep quantity or rhythm disturbances (hypersomnia, insomnia, reversed sleep-wake cycle)
4. Pain (significant degree in at least one location)
- Myalgia: muscle pain, aching, or stiffness
- Arthralgia: joint pain (migratory, without joint swelling or redness)
- Headaches of new type, pattern, or severity
5. Neurological/Cognitive Manifestations (\(\geq\) 2 required)
- Confusion, impaired concentration/short-term memory, disorientation
- Difficulty with information processing, categorizing, word retrieval
- Perceptual/sensory disturbances (spatial instability, disorientation, inability to focus vision)
- Ataxia, muscle weakness, fasciculations
6. At Least ONE Symptom from TWO of the Following Categories:
Autonomic Manifestations: Orthostatic intolerance (neurally mediated hypotension, POTS, delayed postural hypotension), lightheadedness, extreme pallor, nausea and irritable bowel syndrome, urinary frequency/bladder dysfunction, palpitations with or without cardiac arrhythmias, exertional dyspnea
Neuroendocrine Manifestations: Loss of thermostatic stability (subnormal body temperature, marked daily fluctuation), intolerance of extremes of heat and cold, marked weight change, loss of adaptability/worsening symptoms with stress
Immune Manifestations: Tender lymph nodes, recurrent sore throat, recurrent flu-like symptoms, general malaise, new sensitivities to food/medications/chemicals
7. Duration Illness persists \(\geq\) 6 months. May be preceded by various infections or other triggering events.
2 Exclusions
Exclude active disease processes that explain most major symptoms. Comorbid conditions do not exclude diagnosis if they do not explain the constellation of symptoms.
3 Strengths and Limitations
Strengths
- Emphasis on post-exertional malaise as mandatory criterion
- Comprehensive symptom coverage across multiple systems
- Widely adopted in clinical practice
- More specific than Fukuda criteria
Limitations
- Complex algorithm may be difficult to apply consistently
- Selects more severely affected patients (lower sensitivity for mild cases)
- Some symptom requirements (e.g., “significant degree”) lack operational definitions
- Not validated against objective biomarkers or treatment response