The Canadian Consensus Criteria (2003)
Developed by an international panel of clinicians and researchers, the Canadian Consensus Criteria established ME/CFS as a distinct clinical entity with specific symptom requirements. This was a pivotal shift from earlier definitions that relied heavily on unexplained fatigue.
Core Requirements:
- Post-exertional malaise (mandatory)
- Sleep dysfunction
- Pain (muscle, joint, or headaches)
- Neurological/cognitive manifestations
- Autonomic, neuroendocrine, or immune symptoms
IOM Criteria (2015)
The Institute of Medicine report, now sponsored by the National Academy of Medicine, reviewed over 9,000 studies to establish new diagnostic criteria that simplified recognition while maintaining specificity.
Three Core Symptoms Required:
- Substantial reduction in activity level (6+ months)
- Post-exertional malaise
- Unrefreshing sleep
Plus one of: cognitive impairment or orthostatic intolerance
NICE Guidelines NG206 (2021)
The UK's National Institute for Health and Care Excellence updated guidelines that explicitly removed graded exercise therapy (GET) as a recommended treatment, reflecting growing evidence that activity management must respect post-exertional symptom exacerbation.