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A glossary of key ME/CFS-related terms.




B cell - B lymphocyte, or a type of white blood cell, which is involved in the immune response by secreting antibodies to ward off infections. In mammals, they are mostly matured in the bone marrow.

biopsychosocial model (BPS model) - a school of thought, usually based in psychology, which claims illness and disease to be the result of the intermingling of biological, psychological and social causes.


Canadian Consensus Criteria (CCC) - a criteria used to diagnose ME/CFS (sic), developed by a group of clinicians in 2003. Often considered the most complex criteria, with the lowest number of patients meeting the criteria. Led to the development of the International Consensus Criteria in 2011.

Chronic Fatigue Syndrome (CFS) - may be more likely to refer to those diagnosed using the Fukuda Criteria or the Oxford definition. Commonly used in the United States as the name of the disease. Viewed by some patients as dismissive and derogatory.

Chronic Fatigue Syndrome Advisory Committee (CFSAC) - (sometimes pronounced SIF-SACK) met twice per year, covering current topics related to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Meetings usually lasted for two days and the results were presented to the Secretary of Health and Human Services (HHS). After 15 years, on September 5, 2018, CFSAC's charter was not renewed by the Department of HHS, effectively dissolving the committee without notice or warning.

cognitive behavioral therapy (CBT) - A type of psychotherapy geared toward modifying alleged unhealthy thinking, behaviors or illness beliefs. One of the treatment arms used in the controversial PACE Trial.

conversion disorder - formerly known as "hysteria". A mental condition in which neurologic symptoms can not be explained by a medical condition and are believed by some to develop unconsciously. Although symptoms are considered real, conversion disorder is usually thought to be triggered by stress or trauma.

crash - see post-exertional malaise



energy envelope theory - the theory that a person with ME has a limited amount of energy to use each day without causing an exacerbation of symptoms or inducing PEM. This "energy envelope" will vary from day to day and from person to person. See also pacing with a heart rate monitor

enterovirus - a genus of RNA viruses which typically enter the body through the gastrointestinal tract and can sometimes spread to the central nervous system or other parts of the body. Enteroviruses include those which cause polio and coxsackievirus.


Fukuda criteria


graded exercise therapy (GET) - exercise therapy which gradually increases the patient's activity levels. Focuses on overcoming the patient's alleged unhelpful illness beliefs that exertion can exacerbate symptoms, rather than on reversing physical deconditioning. Considered controversial, and possibly harmful, in the treatment or management of ME. One of the treatment arms of the controversial PACE trial.


HLA complex (human leukocyte antigen) - a gene complex responsible for encoding certain proteins which help the immune system to distinguish the body's own proteins from proteins which are made by foreign invaders like bacteria and viruses. See also "Dr Ron Davis’s big immune study is looking at HLA genes"

heart rate monitor (HRM) - a device that measures your heart rate / pulse. Typically a chest strap, wrist strap, or mobile phone app. See also pacing with a heart rate monitor.

heart rate variability (HRV) - a measurement of the specific changes in time (or variability) between successive heart beats. This is related to autonomic and cardiovascular function. See also pacing with a heart rate monitor.


ICD - International Classification of Diseases. A system of medical codes created by the World Health Organization (WHO) for diseases and other health related conditions for the purpose of international consistency. The 11th revision, or ICD-11, is due in 2018.

IOM - Institute of Medicine, (National Academy of Medicine (NAM) as of June 2015) is an American non-profit, non-governmental organization which provides expert advice on issues relating to biomedical science, medicine and health.

Institute of Medicine report - or IOM Report, was published by the Institute of Medicine on February 10 2015. The report Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness proposed the name Systemic Exertion Intolerance Disease (SEID). Among its key findings were that "This disease is characterized by profound fatigue, cognitive dysfunction, sleep abnormalities, autonomic manifestations, pain, and other symptoms that are made worse by exertion of any sort." — "Between 836,000 and 2.5 million Americans suffer from myalgic encephalomyelitis/chronic fatigue syndrome."

International Consensus Criteria

invisible illness - a chronic condition or illness, such as ME/CFS, which may not be apparent to others. Sufferers may look healthy, yet be in poor health. Symptoms of the illness may not be visible and can be misunderstood or go unnoticed by others. Also, patients may wind up secluded or homebound due to the illness and become "invisible".





magnetic levitation device - uses ferrofluid (a liquid which can become magnetized) in a glass capillary tube surrounded by magnets. This creates a density gradient and cells move to their respective densities within the tube. White blood cells in CFS patients have been discovered to be less dense than those of healthy controls, indicating the possible use of the device as an inexpensive diagnostic test. This technology is being developed by Ron Davis' team at Stanford University. See also OMF Funded Diagnostic Technology Development

mass spectrometer - a device which converts molecules to ions, or charged particles. It then uses magnetic and electric fields to sort the ions according to their mass (similar to weight) and charge, and measure their characteristics.

ME - abbreviation for Myalgic Encephalomyelitis

medically unexplained physical symptoms (MUPS) - technically the term means that there is no known medical cause or explanation for the patient's symptoms. However, MUS or MUPS are generally lumped into a psychosomatic, or psychologically caused category by those in the medical profession.

medically unexplained symptoms (MUS) - see medically unexplained physical symptoms

metabolic trap hypothesis - hypothesis proposed by Dr. Robert Phair. Based on preliminary data from the OMF-funded ME/CFS Severely Ill Patient Study (SIPS), which found several genes which may carry mutations in people with ME. These mutations may cause enzymes which process important metabolites to slow down and cause a metabolic trap, which could explain some symptoms in ME/CFS.

metabolite - a substance produced by, or involved in metabolism.

metabolomics - the study and analysis of the chemical processes of metabolites within cells, tissues or organisms.

microbiome - the collective of microscopic organisms (including bacteria, viruses and fungi) and their genetic material, which are present in a particular environment, particularly in the human body.

Millions Missing - a global campaign, first led by #MEAction in May 2016, which aims to gain awareness, community, education, research, funding and treatment equality for Myalgic Encephalomeyelitis. See also #MillionsMissing on Twitter.

mitochondria - organelles or subunits within a cell. Their primary role is to take in nutrients and produce energy for the cell in the form of ATP (adenosine triphosphate). This process requires oxygen and is called aerobic respiration.

Myalgic Encephalomyelitis (ME) - an often devastating illness for which there is little treatment and no cure. An estimated 25% of those suffering with ME are housebound or bedbound. Symptoms include neurological impairments, abnormal energy production, orthostatic intolerance, sleep abnormalities, pain, cognitive impairment, immune dysfunction and gastro-intestinal impairments, among others. A defining symptom of ME is post-exertional malaise (PEM), or post-exertional neuroimmune exhaustion (PENE), which means that even small exertions can exacerbate symptoms and have long-lasting detrimental effects.


NASA 10-minute lean test - variation of a test used by NASA researchers to test for orthostatic intolerance. A simple test which is recommended by the Bateman Horne Center for ME and Fibromyalgia patients. Instructions for medical providers Instructions for patients

nanoneedle - a nanofabricated device (one nanometer = one millionth of a millimeter) which measures electrical impedance from a drop of blood. The electrical impedance increased in the blood cells of 10 ME/CFS patients when stressed with salt, but not in healthy controls. This device may be able to distinguish ME/CFS patients from healthy controls and is being developed by Ron Davis' team at Standford University. See also OMF Funded Diagnostic Technology Development


orthostatic intolerance (OI) - the development of symptoms when standing upright which are relieved when reclining; may be due to dysautonomia

Oxford criteria


PACE trial - a controversial study which claims that CBT and GET are effective in treating CFS/ME. Its results and methodology are disputed by patients, scientists and peer-reviewed scientific literature.

pacing - the practice of staying within one's "energy envelope" by interspersing periods of activity with periods of rest. Patients may use pacing with a heart rate monitor as an objective measure of exertion.

payback - see post-exertional malaise

post-exertional malaise (PEM) - a worsening of ME symptoms due to physical or cognitive exertion

post-exertional neuroimmune exhaustion (PENE) - see post-exertional malaise

postural orthostatic tachycardia syndrome (POTS) - a form of orthostatic intolerance where the cardinal symptom is excessive tachycardia due to changing position (e.g. from lying down to sitting up).

PwME - person with Myalgic Encephalomyelitis (ME)



Ramsay definition - Melvin Ramsay's definition of ME


SEID - Systemic Exertion Intolerance Disease was the name proposed for ME/CFS in the Institute of Medicine report of February 10, 2015.

Seahorse analyzer - an instrument which measures oxygen consumption rate and extracellular acidification rate in live cells, in real time, producing information regarding important cellular functions such as mitochondrial respiration and glycolysis.

Severely Ill Patient Study (SIPS) - a study funded by the OMF (Open Medicine Foundation) and led by Dr. Ronald Davis and Wenzhong Xiao, PhD. It includes over 1000 tests per patient, including the patients' genome, gene expression, metabolomics, microbiome, and many others. See also ME/CFS Severely Ill Big Data Study for details, a complete list of tests and Spring 2018 update.

SF-36 (Short Form (36) Health Survey) - a 36 item patient reported questionnaire, used to determine patient health status and quality of life.

somatic - relating to the physical body. In biology, all the cells of the body, except those which form egg or sperm. Easily confused with "somatoform" or "psychosomatic".

somatoform disorder - a mental health disorder in which a patient experiences symptoms which can not be explained by current medical knowledge. Symptoms are considered real, even though the cause is never found and is assumed to be psychological. Patients who disagree with the psychological diagnosis of somatoform disorder and the lack of further investigation into their symptoms are often met with skepticism or even disdain by the medical community.

Spoon Theory - an analogy which equates the amount of energy or health someone with chronic illness has to complete daily tasks to a limited number of spoons. See also "The Spoon Theory"

spoonie - a person, usually with a chronic illness, with a limited amount of energy or health, or "spoons". See also Spoon Theory


T cell - T lymphocyte, or a type of white blood cell, which is mostly produced or matured in the thymus gland (hence T-cell) and is involved in immune response on a cellular level. See also Dr. Mark Davis Research Update video

two-day cardiopulmonary exercise test

tilt table test



vO2 Max - the maximum volume of oxygen that an individual can utilize during increasingly strenuous exercise, such as on a treadmill. See also two-day cardiopulmonary exercise test


WHO - World Health Organization

World Health Organization (WHO) - "A specialized agency of the United Nations that is concerned with public health. It was established on 7 April 1948, and is headquartered in Geneva, Switzerland. The WHO is a member of the United Nations Development Group. Its predecessor, the Health Organization, was an agency of the League of Nations."[1] The International Statistical Classification of Diseases and Related Health Problems (ICD) is maintained by WHO.





Antibodies or immunoglobulin refers to any of a large number of specific proteins produced by B cells that act against an antigen in an immune response. [1]

Myalgic encephalomyelitis or chronic fatigue syndrome, often used when both illnesses are considered the same.

Cognitive behavioral therapy[citation needed]

Myalgic encephalomyelitis or M.E. has different diagnostic criteria to chronic fatigue syndrome; neurological symptoms are required but fatigue is an optional symptom.Cite error: Closing </ref> missing for <ref> tag

Systematic Exertion Intolerance Disease. A new term with new diagnostic criteria designed to replace chronic fatigue syndrome.Cite error: Closing </ref> missing for <ref> tag

The information provided at this site is not intended to diagnose or treat any illness.
From MEpedia, a crowd-sourced encyclopedia of ME and CFS science and history.