Myalgic encephalomyelitis/chronic fatigue syndrome

Last revised by Daniel J Bell on 21 Oct 2021

Myalgic encephalomyelitis/chronic fatigue syndrome or ME/CFS, is a complex organic disorder, characterized by profound fatigue and associated marked impairment of both physical and mental functioning. Its underlying etiology is undetermined and a curative treatment remains elusive.

In 1934, following the first reports of this new mysterious condition it was named neuromyasthenia. In 1959, it was renamed benign myalgic encephalomyelitis as it began to be thought of as an inflammatory disorder. The Center for Disease Control and Prevention (CDC) in the US in 1987 created a working group, which after much discussion about its nomenclature settled upon the new term "chronic fatigue syndrome". However myalgic encephalomyelitis was internationally in such widespread use by this point, that the condition became known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), its current preferred monicker 4.

Myalgic encephalomyelitis/chronic fatigue syndrome is a worldwide endemic condition and the majority of cases are sporadic in nature although occasionally outbreaks of clustered cases are seen 1. Its prevalence has been estimated as much as 0.5-1% of the adult population.

ME/CFS is seen in all ages, ethnicities and socioeconomic strata. There are two spikes in time of onset, in the second and fourth decades. In teenagers, females predominate 3-4:1. It is thought that as many as 91% of adult patients have not been diagnosed according to accepted criteria 1.

A cardinal feature of myalgic encephalomyelitis/chronic fatigue syndrome is an aggravation of symptoms by even the most minor of physical and/or mental efforts. These symptoms then often may remain for hours, days or weeks despite adequate rest.

  • severe debilitating fatigue and lassitude
  • cognitive disturbances: poor concentration, impaired short term memory, often called "brain fog"
  • disturbed sleep
  • myalgia and arthralgia
  • neurological symptoms
  • autonomic symptoms
    • orthostatic intolerance (OI) is common
    • thermoregulation dysfunction: hypersensitivity to high/low temperatures, low core body temperature
  • immune dysregulation
  • GI symptoms: abdominal discomfort, nausea, loss of appetite

The cause of myalgic encephalomyelitis/chronic fatigue syndrome is not known but is thought to be multifactorial.

It is thought to be a physical illness, not least due to demonstrable biophysical changes. Secondary psychological sequelae may be seen, as in any other chronic disease process 1

Imaging for myalgic encephalomyelitis/chronic fatigue syndrome per se is usually normal. However, imaging may be important when patients present with troubling neurological deficits and other serious diseases of the CNS need to be excluded 1. Structural and functional neuroimaging have demonstrated changes in the brain 3.

Many myalgic encephalomyelitis/chronic fatigue syndrome patients may have decreased heart size on imaging, e.g. decreased cardiothoracic ratio (CTR) on chest radiographs 2.

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