← Home
Atlas Guide
What is ME/CFS?
Myalgic Encephalomyelitis / Chronic Fatigue Syndrome is a chronic, multi-system disease defined by its hallmark feature: post-exertional malaise.
Quick read · 30 sec
ME/CFS (Myalgic Encephalomyelitis/Chronic Fatigue Syndrome) is a chronic, multi-system disease. Its hallmark is post-exertional malaise (PEM) — a worsening of symptoms after physical, cognitive, or emotional exertion.
- Affects an estimated 15–30 million people worldwide
- Not explained by other medical conditions
- Not caused by deconditioning or lack of exercise
- Not a psychiatric condition
- Involves measurable biological abnormalities
- No approved cure currently exists
Standard · 3 min
Core Features
PEM is the hallmark of ME/CFS — a worsening of symptoms following physical, cognitive, or emotional exertion, often delayed by 12–72 hours and disproportionate to the effort involved. Rest does not reliably resolve it.
What ME/CFS is Not
State of the Evidence
What We Know
- Immune dysfunction is consistently documented
- Metabolic abnormalities found in multiple studies
- Reduced cerebral blood flow during tilt testing replicated
- Two-day CPET shows objective post-exertional malaise
- PEM distinguishes ME/CFS from other fatiguing conditions
What We Think
- Neuroinflammation may be a key mechanism
- A hypometabolic state may underlie the energy deficit
- Autoimmune processes may be involved in some patients
- Gut microbiome changes may contribute to symptoms
What We Don't Know
- What triggers the disease in each individual
- Whether it's one disease or several with similar presentations
- How to reliably cure or reverse it
- Why severity varies so much between patients
- The precise mechanism of post-exertional malaise
Diagnostic Criteria
Severity Spectrum
Deep dive · 10+ min