ME/CFS
Myalgic encephalomyelitis / chronic fatigue syndrome. A long-term, multi-system illness. See What is ME/CFS?
PEM: post-exertional malaise
The delayed crash after doing more than your body can manage. The hallmark of ME/CFS. See Symptoms.
Pacing
Managing activity to stay inside your energy limits and avoid PEM. See Pacing.
Energy envelope
The amount of activity you can do without triggering PEM. It changes over time.
Boom-bust
Overdoing it on good days, then crashing. The most common path to getting worse.
Long COVID
Ongoing symptoms after COVID-19. Many people with Long COVID meet ME/CFS criteria.
OI: orthostatic intolerance
Symptoms that worsen when upright and improve lying down.
POTS
Postural orthostatic tachycardia syndrome. Heart rate rises by 30+ beats per minute on standing. See POTS.
Hypocapnic cerebral hypoperfusion
Reduced blood flow to the brain when upright, caused by breathing out too much carbon dioxide. It can happen without a racing heart.
Autonomic nervous system
The automatic part of the nervous system that controls heart rate, blood pressure, digestion and temperature.
Dysautonomia
Any malfunction of the autonomic nervous system. POTS is one type.
Neuroinflammation
Inflammation in the brain or nervous system.
Glymphatic system
The brain’s waste-clearance system, which works mostly during sleep. Found to be impaired in ME/CFS in 2026.
Mitochondria
The “energy factories” inside cells that make ATP using oxygen.
ATP
The cell’s energy currency.
Anaerobic metabolism
The inefficient backup way cells make energy without enough oxygen, producing lactate. Tips in too early in ME/CFS.
NAD⁺ / NADH
Electron carriers needed for energy production. NADH is also a supplement.
NMN / NR
Nicotinamide mononucleotide / nicotinamide riboside. Supplements the body converts into NAD⁺.
CoQ10 / ubiquinol
Coenzyme Q10, part of the energy-production chain. Ubiquinol is its active form.
ALC
Acetyl-L-carnitine. Helps carry fuel into mitochondria.
DMG
Dimethylglycine. An ingredient in some supplement blends.
TRPM3
A calcium ion channel that Griffith University found doesn’t work properly on immune cells in ME/CFS.
NK cells
Natural killer cells, immune cells that fight viruses.
Autoantibodies
Antibodies that target the body’s own tissues. Found in some people with ME/CFS.
Immunoadsorption
A blood-filtering procedure that removes antibodies.
TSPO
A protein targeted in PET scans to show immune activity or energy changes.
BBB: blood-brain barrier
The protective lining that controls what passes from blood into the brain.
EBV: Epstein-Barr virus
The virus that causes glandular fever. A common ME/CFS trigger. It stays in the body and can reactivate.
CMV: cytomegalovirus
A related herpes-family virus that can also reactivate.
VCA IgM / IgG
EBV antibody tests. IgM suggests recent or active infection; IgG shows past exposure.
EBNA
EBV nuclear antigen antibody. Appears months after infection and helps date it.
EA
EBV early antigen antibody. Rises when EBV reactivates.
LD / LDH
Lactate dehydrogenase, an enzyme that leaks from stressed cells. See Tests.
LD isoenzymes
The five forms of LD (LD1–LD5). The mix shows which tissue it came from.
CK
Creatine kinase, a marker of muscle damage.
CRP / ESR
Blood markers of general inflammation. Usually very low in ME/CFS.
Ferritin
A measure of your iron stores.
Homocysteine
A blood marker that rises if you’re functionally short of B12 or folate.
Tryptase
A blood marker of mast cell activity (allergic-type reactions).
HRV: heart rate variability
The variation between heartbeats. A drop can warn of a crash 1–2 days ahead.
AHI
Apnoea-hypopnoea index. Breathing events per hour in a sleep study.
OSA
Obstructive sleep apnoea.
CPAP
Continuous positive airway pressure. A machine that keeps the airway open during sleep.
LDN
Low-dose naltrexone. See Medications.
HBOT
Hyperbaric oxygen therapy. Breathing oxygen in a pressurised chamber.
IHHT
Intermittent hypoxia-hyperoxia therapy. Breathing air that alternates between low and high oxygen.
GET
Graded exercise therapy. Increasing exercise on a schedule. Now recognised as harmful in ME/CFS.
CBT
Cognitive behavioural therapy. Can support coping, but isn’t a cure for ME/CFS.
CCC
Canadian Consensus Criteria, a diagnostic definition often used in trials.
ICC
International Consensus Criteria, a stricter diagnostic definition.
IOM / NAM criteria
The 2015 US Institute of Medicine (now National Academy of Medicine) diagnostic criteria.
Fukuda criteria
An older, broad definition of CFS that doesn’t require PEM.
Bell score
A 0–100 disability scale used in ME/CFS. Lower means more disabled.
RCT
Randomised controlled trial. The strongest kind of evidence.
Placebo
A dummy treatment used for comparison. In ME/CFS, 20–40%+ of people feel better on placebo.
Open-label
A study where everyone knows what treatment they’re getting. There’s no placebo, so results are less reliable.
Off-label
Using an approved drug for a condition it isn’t officially approved for.
Biomarker
A measurable sign of disease, like a blood test result.
Polygenic
Influenced by many genes, each with a small effect.
ANZCTR
Australian New Zealand Clinical Trials Registry.
NCNED
National Centre for Neuroimmunology and Emerging Diseases, Griffith University.
TGA
Therapeutic Goods Administration, Australia’s medicines regulator.
NHMRC
National Health and Medical Research Council, Australia’s main medical research funder.
NICE
National Institute for Health and Care Excellence (UK). Its 2021 ME/CFS guideline rejected GET.
OT
Occupational therapist. Helps with pacing, energy management and daily living.
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