Medical Matters > Post-Viral Fatigue Syndrome, Myalgic Encephalomyelitis or Encephalopathy, Chronic Fatigue Syndrome, and Long Covid

ME Essential Winter 2022


Please can you define what PVFS, ME/CFS, and Long Covid mean. I am having difficulty determining if they are the same disease or different. Thank you!


Post-Viral Fatigue Syndrome (PVFS) was introduced during the 1980s as a description for patients who could clearly trace the onset of their illness back to a viral infection. PVFS can be diagnosed if a person experiences symptoms that continue to cause functional limitations i.e., has been unable to make a full recovery within the expected timeframe. Historically it would often precede a diagnosis of ME/CFS but with the 2021 NICE Clinical Guideline, ME/CFS should now be considered after a minimum of 6 weeks of symptoms developing (see below), and PVFS is less likely to be used.


The World Health Organisation’s authoritative International Classification of Diseases (ICD-11 2022) recognises Post-Viral Fatigue Syndrome as the parent term in Section 8: Diseases of the Nervous System, Sub-section: other disorders of the nervous system: 8E49.

Both Myalgic Encephalomyelitis and Chronic Fatigue Syndrome are included terms in this category, while ‘Fatigue’ is an exclusion and determined to be a general clinical symptom.

The NHS employs diagnostic codes based on the ICD in its SNOMED-CT digital classification system and similarly recognises PVFS, ME and CFS as being neurological.

While SNOMED-CT has chosen to use ‘Chronic Fatigue Syndrome’ as the parent term, Post-Viral Fatigue Syndrome and Myalgic Encephalomyelitis or Myalgic Encephalopathy, can also be used on a patient’s medical record.

Additionally, the NHS system carries coding for the diagnosis of Post-acute Covid-19 or Long Covid-19 as ‘disorders following viral disease’.

ME (Myalgic Encephalomyelitis) is a name that was originally introduced in a Lancet editorial (The Lancet 1956) to describe people with the illness who had been admitted to London’s Royal Free Hospital in 1955. Clinically, myalgic was used to refer to the characteristic muscle symptoms, and encephalomyelitis to the brain symptoms. Pathologically, encephalomyelitis indicates inflammation within the brain and spinal cord – a description for which there is currently no sound scientific evidence.

CFS (Chronic Fatigue Syndrome) is the name currently favoured by the UK medical profession because it makes no firm assumption about cause. However, it is widely disliked and viewed as inappropriate by the patient community who believe that the name perpetuates misunderstandings about causation and management of the disease and results in dismissive attitudes from both healthcare providers and the general public.

Two major criticisms of CFS as a name are that it fails to reflect the diverse symptomatology and severity of the illness and that it has become a convenient label for anyone with persistent unexplained fatigue. The ME Association shares these concerns and will continue to campaign to change medical opinion. We feel that using ‘Chronic Fatigue Syndrome’ is rather like using ‘chronic forgetfulness syndrome’ to describe Dementia.

The current situation

The term ‘encephalomyelitis’ is not a pathologically proven explanation for what may be happening in the nervous system in ME/CFS. Consequently, its use can cause dissent among doctors although it is favoured as a historical term by some in the patient community.

The ME Association proposed a new term, ‘encephalopathy’ (a significant disorder of brain function), as an alternative to try and gain greater acceptance from the medical community. This was accepted overwhelmingly by the charity’s members, and we became The Myalgic Encephalopathy Association in 2001.

We believe that ‘Myalgic Encephalopathy’ is a more appropriate way of describing the various abnormalities in hypothalamic, autonomic and cognitive functions and in cerebral perfusion that have been reported in the research literature.

While this term has been accepted by NICE, the DHSC, some researchers and doctors, the debate continues and is likely to remain unsettled until research is able to conclusively determine what causes and perpetuates this disease.

Until this happens, we have also adopted the more inclusive abbreviation ME/CFS in the literature and on the website etc., as has NICE in the 2021 Clinical Guideline.

The NICE Clinical Guideline on ME/CFS (Oct. 2021)

The ME Association took a key role in the development of the 2021 NICE Guideline, and we support its recommendations. Anyone with a suspected or confirmed diagnosis should try and read the Guideline and work with their GP or ME/CFS specialist service to ensure their diagnosis is correct and that appropriate health and social care services are provided.

Severity of ME/CFS

Definitions of severity are not clear cut because individual symptoms vary widely in severity and people may have some symptoms more severely than others. The definitions below provide a guide to the level of impact of symptoms on everyday functioning.


People with mild ME/CFS care for themselves and do some light domestic tasks (sometimes needing support) but may have difficulties with mobility. Most are still working or in education, but to do this they have probably stopped all leisure and social pursuits. They often have reduced hours, take days off and use the weekend to cope with the rest of the week.

Moderate ME/CFS

People with moderate ME/CFS have reduced mobility and are restricted in all activities of daily living, although they may have peaks and troughs in their level of symptoms and ability to do activities. They have usually stopped work or education, and need rest periods, often resting in the afternoon for 1 or 2 hours. Their sleep at night is generally poor quality and disturbed.

Severe ME/CFS

People with severe ME/CFS are unable to do any activity for themselves or can carry out minimal daily tasks only (such as face washing or cleaning teeth). They have severe cognitive difficulties and may depend on a wheelchair for mobility. They are often unable to leave the house or have a severe and prolonged after-effect if they do so. They may also spend most of their time in bed and are often extremely sensitive to light and sound.

Very severe ME/CFS

People with very severe ME/CFS are in bed all day and dependent on care. They need help with personal hygiene and eating and are very sensitive to sensory stimuli. Some people may not be able to swallow and may need to be tube fed.

1.2 Suspecting ME/CFS

1.2.1 Explain to people presenting with possible symptoms of ME/CFS that there currently is no diagnostic test for ME/CFS, and it is recognised on clinical grounds alone.

1.2.2 Suspect ME/CFS if:

  • the person has had all of the persistent symptoms (below) for a minimum of 6 weeks in adults and 4 weeks in children and young people and,
  • the person's ability to engage in occupational, educational, social or personal activities is significantly reduced from pre‑illness levels and,
  • symptoms are not explained by another condition.

All of these symptoms should be present:

  • Debilitating fatiguethat is worsened by activity, is not caused by excessive cognitive, physical, emotional or social exertion, and is not significantly relieved by rest.
  • Post-exertional malaiseafter activity in which the worsening of symptoms:
    • is often delayed in onset by hours or days,
    • is disproportionate to the activity,
    • has a prolonged recovery time that may last hours, days, weeks or longer.
  • Unrefreshing sleepor sleep disturbance (or both), which may include:
    • feeling exhausted, feeling flu-like and stiff on waking,
    • broken or shallow sleep, altered sleep pattern or hypersomnia.
  • Cognitive difficulties (sometimes described as ‘brain fog'), which may include problems finding words or numbers, difficulty in speaking, slowed responsiveness, short-term memory problems, and difficulty concentrating or multitasking.

1.2.4 Be aware that the following symptoms may also be associated with, but are not exclusive to, ME/CFS:

  • orthostatic intolerance and autonomic dysfunction, including dizziness, palpitations, fainting, nausea on standing or sitting upright from a reclining position
  • temperature hypersensitivity resulting in profuse sweating, chills, hot flushes, or feeling very cold
  • neuromuscular symptoms, including twitching and myoclonic jerks
  • flu-like symptoms, including sore throat, tender glands, nausea, chills or muscle aches
  • intolerance to alcohol, or to certain foods and chemicals
  • heightened sensory sensitivities, including to light, sound, touch, taste and smell
  • pain, including pain on touch, myalgia, headaches, eye pain, abdominal pain or joint pain without acute redness, swelling or effusion.

Long Covid

NICE provide the following definitions in its Rapid Guideline on the long-term effects of Covid-19:

Post-COVID-19 syndrome

  • Signs and symptoms that develop during or after an infection consistent with COVID‑19, continue for more than 12 weeks and are not explained by an alternative diagnosis.
  • It usually presents with clusters of symptoms, often overlapping, which can fluctuate and change over time and can affect any system in the body.
  • Post‑COVID‑19 syndrome may be considered before 12 weeks while the possibility of an alternative underlying disease is also being assessed.
  • In addition to the clinical case definitions, the term ‘Long COVID’ is commonly used to describe signs and symptoms that continue or develop after acute COVID‑19. It includes both ongoing symptomatic COVID‑19 (from 4 to 12 weeks) and post‑COVID‑19 syndrome (12 weeks or more).

It is the opinion of the ME Association and an increasing number of researchers and clinicians that Long Covid could be regarded as another form of Post-Viral Fatigue Syndrome just like ME/CFS is for a lot of people. Indeed, many with Long Covid are being shown in research studies to meet the diagnostic criteria for ME/CFS especially if key symptoms and functional limitations persist 12 weeks after Covid-19.

Long Covid is triggered by an infection just as ME/CFS is for the majority of people, it shares key symptoms, has a direct effect on energy, and can lead to a similar degree of functional impairment. However, the Covid-19 infection can also cause organ damage which is different than in ME/CFS.

Following the 2020-2022 Covid pandemic, more people are having to live with the effects of Long Covid months or years after the initial infection and some are being re-diagnosed with ME/CFS. In 2022, the ONS estimated that 1.8 million adults and children might have Long Covid compared with an estimated 260,000 who have an ME/CFS that was not triggered by Covid-19. Both conditions represent a considerable challenge to patients and family members, the NHS, social care services and the welfare system.

NHS England responded to the needs of people with Long Covid by establishing – as they did for people with ME/CFS – a network of Long Covid clinics. These can be accessed by referral from a GP and provide diagnostic and triaging services. Specialists working in these secondary care services should also be able to provide tailored management advice and support to people who are struggling to cope with either condition – especially those severely or very severely affected.

The ME Association is campaigning to ensure these specialist services are improved and made available across the UK particularly in the devolved nations where services are lacking. Management practices should be aligned as both conditions can benefit from the safe and effective approach known as Pacing, until such time as specific treatments can be developed.

NICE Rapid Guideline: Managing the long-term effects of COVID-19 (Nov. 2022)

Common Symptoms of Long Covid

Symptoms after acute COVID-19 are highly variable and wide ranging. The most commonly reported symptoms include (but are not limited to) the following:

Respiratory symptoms:
  • Breathlessness
  • Cough.
Gastrointestinal symptoms:
  • Abdominal pain
  • Nausea and vomiting
  • Diarrhoea
  • Weight loss and reduced appetite.
Cardiovascular symptoms:
  • Chest tightness
  • Chest pain
  • Palpitations.
Musculoskeletal symptoms:
  • Joint pain
  • Muscle pain.
Generalised symptoms:
  • Fatigue
  • Fever
  • Pain.
Dermatological symptoms:
  • Skin rashes
  • Hair loss.
Neurological symptoms:
  • Cognitive impairment (‘brain fog’, loss of concentration or memory issues)
  • Headache
  • Sleep disturbance
  • Peripheral neuropathy symptoms (pins and needles and numbness)
  • Dizziness
  • Delirium (in older populations)
  • Mobility impairment
  • Visual disturbance.
Ear, nose and throat symptoms:
  • Tinnitus
  • Earache
  • Sore throat
  • Dizziness
  • Loss of taste and/or smell
  • Nasal congestion.
Psychological/psychiatric symptoms:
  • Symptoms of depression
  • Symptoms of anxiety
  • Symptoms of post-traumatic stress disorder.

The following symptoms and signs are less commonly reported in children and young people than in adults:

  • shortness of breath
  • persistent cough
  • pain on breathing
  • palpitations
  • variations in heart rate
  • chest pain.

Abbreviations used above:
NICE = The National Institute for Health and Care Excellence, DHSC = The Department of Health and Social Care, ONS = Office for National Statistics.





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Information provided by The ME Association should not be construed as medical advice. Don't assume any new or worsened symptoms are simply the result of having ME/CFS or Long Covid. We recommend that any information you deem relevant is discussed with your NHS GP as soon as possible. It is important that you seek personalised medical advice from the GP who is in charge of your care and who knows you well.

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