The history of myalgic encephalomyelitis

The history of myalgic encephalomyelitis (ME) is that of an illness observed for nearly a century, yet whose understanding has progressed far more slowly than scientific knowledge.

Over the decades, doctors have described similar symptoms in different regions of the world: profound exhaustion, pain, neurological disturbances, exercise intolerance, and worsening after even minimal activity.

Yet despite repeated observations, medical research, and international recognition, ME/CFS has long faced misunderstanding, minimisation, and significant diagnostic delays.

This timeline retraces the key milestones that have marked its history: from the first documented outbreaks to recent advances linked in particular to research on post-infectious illnesses and long Covid.

1934 – Los Angeles (United States): a first major documented outbreak

1934 – Los Angeles County General Hospital An outbreak affects the medical staff of a Los Angeles hospital while poliomyelitis is spreading in the region.

Nearly 200 staff members then develop an unusual illness with characteristics different from classic poliomyelitis: extreme exhaustion, muscle pain, neurological disturbances, hypersensitivity to light and noise, and an abnormally long recovery.

Several descriptions of this outbreak show significant similarities with what would later be described under the term myalgic encephalomyelitis.

However, in the absence of a clear medical explanation at the time, these cases remain difficult to interpret and gradually fade from medical memory.

This period nevertheless marks one of the first modern descriptions of a syndrome that would be observed repeatedly throughout the 20th century.

1955 – Royal Free Hospital (London, United Kingdom): birth of the term “myalgic encephalomyelitis”

1955 – Royal Free Hospital A new outbreak occurs in one of the United Kingdom’s most prestigious hospitals.

Within a few weeks, several hundred hospital staff develop similar symptoms: major exhaustion, pain, neurological disturbances, nervous system disruption, and inability to resume normal activity without worsening.

The outbreak draws the attention of British physician Dr Melvin Ramsay, who studies the patients and describes a distinct illness.

Ramsay observes neurological signs in particular that do not correspond to simple fatigue or a psychological disorder. He then proposes the term: Myalgic Encephalomyelitis (myalgic encephalomyelitis).

His work would contribute durably to the recognition of an illness characterised by complex involvement, notably of the nervous system.

1969 – International recognition by the World Health Organization

1969 – WHO The World Health Organization includes myalgic encephalomyelitis in its International Classification of Diseases.

It is then classified among neurological diseases, under the historical ICD-10 code G93.3.

This recognition represents a major milestone: ME is officially considered a medical illness and not simply a state of fatigue or a psychological reaction.

However, despite this international recognition, the following decades would show that scientific and social acceptance of the illness would remain difficult for a long time.

1970 – A turning point in the history of the illness

1970 – McEvedy and Beard (United Kingdom) A few years after WHO recognition of ME, two British psychiatrists, Colin McEvedy and Andrew Beard, publish an analysis of the Royal Free Hospital outbreak.

They propose an interpretation different from that of Dr Ramsay and question the existence of a distinct neurological illness, advancing the hypothesis of a collective psychological reaction.

This publication would have a significant influence on the perception of the illness for several decades, notably by reinforcing the mistaken idea that symptoms would be primarily linked to psychological factors.

This period marks the beginning of a long scientific and social controversy around ME, which would have important consequences for patients in terms of recognition, research, and care.

1984 – Incline Village (United States): a new alert

1984 – Incline Village, Nevada Thirty years after the Royal Free outbreak, a new series of cases draws the attention of physicians in the United States.

In the Lake Tahoe region, physicians Paul Cheney and Daniel Peterson observe several hundred patients presenting an unusual combination of symptoms: profound exhaustion, pain, cognitive disturbances, sleep disorders, and worsening after exertion.

Initial suspicions focus on an infectious origin, notably due to the clustered occurrence of cases and research around the Epstein-Barr virus.

The CDC (Centers for Disease Control and Prevention) is then called upon to study this situation.

This investigation would contribute to the emergence of a new name: Chronic Fatigue Syndrome (CFS), or chronic fatigue syndrome.

1988 – Official emergence of the term “Chronic Fatigue Syndrome”

1988 – Holmes et al. (CDC) To establish a definition usable for research, the CDC publishes a first operational definition of Chronic Fatigue Syndrome (CFS).

This definition makes it easier to identify patients in scientific studies, but it also contributes to widely disseminating a name centred on fatigue, to the detriment of the illness’s other major characteristics.

For many patients and researchers, this name does not reflect the complexity of the illness, notably its neurological, immune, and post-infectious nature.

1994 – The Fukuda criteria

1994 – CDC, United States Researchers publish the Fukuda criteria, which become for several years the international reference for defining patients included in chronic fatigue syndrome studies.

These criteria notably require persistent fatigue for at least six months, associated with several additional symptoms such as sleep disturbances, pain, or cognitive difficulties.

They allow better standardisation of research, but their relatively broad definition also leads to great heterogeneity in the populations studied.

Some patients meeting the criteria of historical ME can thus be mixed with people presenting other causes of chronic fatigue.

2003 – The Canadian Consensus Criteria

2003 – Canadian Consensus Criteria (CCC) International researchers propose new diagnostic criteria aimed at better characterising myalgic encephalomyelitis.

Unlike previous criteria, they give central importance to post-exertional malaise (PEM), considered an essential element of the illness.

These criteria also describe other important dimensions: neurological disturbances, sleep disruption, pain, and immune and autonomic system dysfunction.

They contribute to gradually bringing the scientific definition of the illness closer to Ramsay’s historical description.

2011 – The International Consensus Criteria

2011 – International Consensus Criteria (ICC) International experts propose a new definition centred on myalgic encephalomyelitis.

These criteria deliberately abandon the use of the term “chronic fatigue syndrome”, considered insufficient to describe the complexity of the illness.

They emphasise in particular:

• post-exertional malaise;
• neurological disturbances;
• immune system abnormalities;
• energy metabolism disruption.

This publication represents an important step in returning to a vision closer to the ME historically described.

2015 – Institute of Medicine report (United States)

2015 – Institute of Medicine (IOM, now National Academy of Medicine) Facing the many persistent difficulties around diagnosis, research, and care, the Institute of Medicine publishes a major report entitled: “Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness”.

After analysing thousands of scientific studies, the report concludes that ME/CFS is a complex, serious, and disabling biological illness, and not a simple disorder linked to fatigue or psychological factors.

The experts emphasise in particular the importance of:

• Post-exertional malaise , considered a major characteristic of the illness;
• Unrefreshing sleep ;
• Cognitive impairment ;
• Orthostatic intolerance in many patients.

The report also proposes the term SEID (Systemic Exertion Intolerance Disease) to better reflect the reality of the illness.

Although this new name is little adopted by the scientific community and patients, this report constitutes an important step in the institutional recognition of ME/CFS in the United States.

2020 – The Covid-19 pandemic changes the view of post-infectious illnesses

2020 – Emergence of long Covid The Covid-19 pandemic gives rise to a phenomenon observed in a significant number of people: the persistence of symptoms several weeks or several months after the initial infection.

In some patients with long Covid, researchers observe manifestations close to those long described in ME/CFS:

• post-exertional malaise;
• persistent profound fatigue;
• cognitive disturbances;
• autonomic nervous system disturbances;
• physical activity intolerance.

This situation leads to renewed scientific interest in post-infectious illnesses and helps raise awareness of the existence of ME/CFS among the general public and the medical world.

Long Covid does not constitute proof that all forms of ME/CFS share the same origin, but it reminds us that an infection can sometimes lead to prolonged and complex consequences far beyond the acute phase of the illness.

2021 – New international recommendations

2021 – NICE (United Kingdom) The National Institute for Health and Care Excellence (NICE) publishes a new guideline dedicated to ME/CFS.

This publication marks an important evolution in the approach to the illness.

It notably recognises:

• the complex and disabling nature of ME/CFS;
• the importance of post-exertional malaise in diagnosis;
• the need for individual adaptation of activity according to the patient’s capacity.

Previous approaches consisting of imposing a progressive and predefined increase in physical activity are no longer recommended as standard treatment.

This evolution represents a major change after several decades during which some patients reported worsening of their condition following unsuitable programmes.

2021 – International Classification of Diseases (ICD-11)

2021 – World Health Organization In the new International Classification of Diseases (ICD-11), ME/CFS remains classified in the domain of neurological diseases.

It appears under the code: 8E49 – Postviral fatigue syndrome, which notably includes myalgic encephalomyelitis and chronic fatigue syndrome.

This continuity confirms that the WHO maintains the listing of this illness in an international medical classification.

2026 – A major evolution in recognition in France

August 2026 – French Assurance Maladie Nearly a century after the first major descriptions of the illness, the French Assurance Maladie publishes an official page dedicated to myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS).

This evolution represents an important step in the institutional recognition of the illness in France.

ME/CFS is presented there as a chronic illness that can be profoundly disabling, with notably:

• significant and lasting exhaustion;
• characteristic post-exertional malaise;
• possible cognitive disturbances;
• manifestations linked to the autonomic nervous system.

This official communication also helps clarify that ME/CFS must not be reduced to simple fatigue or a psychological disorder.

It comes in a context where research on post-infectious illnesses, notably through work on long Covid, has profoundly renewed scientific interest in this illness.

A history that continues to be written

From the first hospital outbreaks to current research on immune, neurological, and energy mechanisms, each step has made it possible to better understand this complex illness.

However, despite these advances, many challenges remain: improving diagnosis, training healthcare professionals more extensively, developing effective treatments, and ensuring that every person who is ill is recognised and supported.

The history of ME/CFS is not finished.
It continues to be written today.

Main sources

This historical page draws on recognised medical, institutional, and scientific publications so that everyone can find the original sources.

• World Health Organization (WHO) International Classification of Diseases (ICD) – Recognition of myalgic encephalomyelitis in international classifications.
• Ramsay AM Historical work on myalgic encephalomyelitis following the Royal Free Hospital outbreak (1955).
• McEvedy CP & Beard AW (1970) “Royal Free epidemic of 1955: a reconsideration”
  Publication proposing a different interpretation of the Royal Free outbreak.
• Holmes GP et al. (1988) “Chronic fatigue syndrome: a working case definition”
  First operational definition of Chronic Fatigue Syndrome published by the CDC.
• Fukuda K et al. (1994) “The chronic fatigue syndrome: a comprehensive approach to its definition and study”
  International criteria used for many years in chronic fatigue syndrome research.
• Carruthers BM et al. (2003) “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols”
  Canadian consensus criteria placing particular emphasis on post-exertional malaise.
• Carruthers BM et al. (2011) “International Consensus Criteria for Myalgic Encephalomyelitis”
  International criteria refocusing the definition around myalgic encephalomyelitis.
• Institute of Medicine / National Academy of Medicine (2015) “Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness”
  Major report on the medical and scientific recognition of ME/CFS.
• NICE Guideline NG206 (2021) “Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management”
  British recommendations on diagnosis and management.
• World Health Organization – ICD-11 (2021) International Classification of Diseases – code 8E49.
• Assurance Maladie française (2026) Official information page dedicated to myalgic encephalomyelitis / chronic fatigue syndrome.

About this timeline

The history of ME/CFS remains an evolving field. Some historical interpretations are still the subject of discussion among researchers.

This page aims to present the main known and documented stages in the evolution of knowledge, from the first observations to current advances.

It does not replace the original scientific publications, but seeks to make this history accessible to as many people as possible.