Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex illness with a complex history. The best way to understand ME/CFS as we know it today is to understand the history of how it was first defined and how the diagnostic criteria has evolved over the past few decades.
Summary of the major diagnostic criteria from 1988 onwards.
What's in a name after all?
In the 19th century the concept of ‘neurasthenia’ was introduced by the psychiatrist George Beard, which defined an illness largely in women that had many of the hallmarks of ME/CFS.
Its onset was generally triggered by an infection and it was described as a "...condition of nervous exhaustion, characterized by undue fatigue on [the] slightest exertion, both physical and mental... the chief symptoms are headache, gastrointestinal disturbances, and subjective sensations of all kinds". The popularity of ‘neurasthenia’ declined in the early stages of the 20th century as its usefulness and validity were called into question.
and the first definition of ME
Around 70 possible outbreaks of ME/CFS were documented during the course of the 20th century. At this point, the condition went by many names but all were linked by their unknown cause and similar symptom set.
One of the most important for the history of ME/CFS was the outbreak at the Royal Free Hospital in the UK. Over 200 staff were hospitalized and the hospital closed for several months due to an unknown illness, it was during this time that Dr. Melvin Ramsay (from the Royal Free Infectious Diseases department) would call the illness Myalgic Encephalomyelitis (ME).
Several years later the condition would be recognized by the World Health Organization in 1969 and Dr. Ramsay’s description (published in 1986) remains one of the best clinical descriptions of the illness.
Several significant US outbreaks led the CDC to put together a working group to reach a consensus on the definition and clinical description of these illnesses.
This group recognized that the many outbreaks had to be known by many other names, including ME. They put together the first description of Chronic Fatigue Syndrome (CFS) in 1988 in order to classify the disease population to improve comparability and reproducibility for research purposes.
In 1994, the definition of CFS was loosened. This criteria has since been criticized for its broad definition that significantly increases the chances of misdiagnosis and impacts the effectiveness research. Furthermore, the name has been faulted for misrepresenting the severity of the illness.
It is also worth noting the requirement of substantial impairment and disturbances in cognition, immune system, autonomic nervous system, and endocrine system. This was further refined in 2011 by the International Consensus Criteria (ICC). This was the first definition to not include fatigue as a required symptom and most similarly represents the definitions of ME from Dr. Ramsay several decades earlier. By removing fatigue, the ICC put more emphasis on the other symptoms of the disorder in an effort to refine the diagnosis to a set of symptoms distinct from other chronic disorders.
Following the evolution of the diagnostic criteria over 2 decades, the quality and consistency of research began to improve. The increased specificity of the diagnostic criteria has resulted in tighter cohorts for comparison to healthy controls in research studies. This increased specificity may result in reduced prevalence as those who do not experience core features of the disease are no longer included.
The Institute of Medicine recommended new criteria in 2015 that reduced the complexity of the ME/CFS definitions of 2003 and 2011 while focusing on a small set of required symptoms most unique to ME/CFS. UK’s NICE adopted similar criteria for ME/CFS in 2021. The Institute of Medicine had also recommended the name “Systemic Exertion Intolerance Disorder” (SEID) for its criteria but this new name was not adopted and ME/CFS was adopted instead.
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