What do the terms CFS and M.E. mean?

Are they the same?

The short answer is that they are the same. M.E. was first used in the UK, and CFS was first used in the USA, and both terms have been used to describe the same problem. The NHS has for many years used the combined term "CFS/ME" and is moving towards using the term "ME/CFS". There is some debate about what to call the condition, however, so we have provided a longer answer below in case some people wanted to know more.

CFS is short for "Chronic Fatigue Syndrome", which is a term that was first used in America by the Centres for Disease Control and Prevention (CDC) in 1988. The CDC recognised that there were people who were becoming ill with infections, and not recovering in the usual timescale. They developed a list of key symptoms that they would expect to see, and these were refined in 1994 into the "Fukuda criteria” for CFS, named after Dr Fukuda, an infectious diseases specialist who was the first author of the paper that they were published in. The list of symptoms included:

  • Fatigue
  • Memory and concentration problems
  • Sore throat
  • Tender lymph nodes
  • Muscle pain
  • Multi-joint pain
  • Headaches
  • Unrefreshing sleep
  • Post-exertional malaise

M.E. is short for "Myalgic encephalomyelitis", which is a term that was first used in the UK after an outbreak of a serious infection at the Royal Free Hospital in 1955. M.E. has since been seen as a post-infective syndrome, and we know that some patients can remain unwell for a long time following debilitating infections. The "myalgic" refers to muscle pain, which is a widespread pain which is commonly experienced by people living with M.E. The “itis” ending of the word "encephalomyelitis" refers to inflammation, in this case inflammation of the brain, which was originally thought to be the cause of the problem. We now know that M.E. is not caused by inflammation of the brain as a whole, so some people have argued that M.E. should be renamed as "Myalgic encephalomyelopathy", as “opathy” means a disease or disorder. However, some recent research looking at the brain's own immune and inflammatory process at a very detailed level has suggested that inflammation of the brain may after all be part of the explanation for ME. Much more research is required before we can piece together a full biological understanding of the condition.

There are now around 20 different case definitions for Chronic Fatigue Syndrome and M.E. which are used around the world, and other names have been proposed. This can lead to confusion and a lot of debate, which has become heated at times. Because the biology of the condition is not fully understood, there is no way of resolving this uncertainty at present, although it is now looking likely that research will help us to get a better understanding of the condition and may lead to clearer names for it. In the meantime, since 2021 the NHS calls the condition M.E./CFS, to acknowledge the different terms which are used around the world.

It is also likely that there will be "subgroups" that will be identified in the future, some of which may group people according to their dominant symptoms. For example, there seems to be a subgroup of people for whom headaches are a more significant problem, whereas some other people living with M.E./CFS don't suffer significantly from headaches. It may also be that the different triggers for M.E./CFS could help us to identify "subgroups". For example, some people identify infections as a trigger, whereas other people identified stress or trauma as a trigger: some people also identify both infections and stress as dual triggers. Once we know more about these subgroups it may be possible to rename some of the subgroups in a way that makes them more meaningful.

The term "Chronic Fatigue Syndrome" is not popular with some people living with the condition, because there are people who don't understand the difference between fatigue and tiredness. The term CFS also doesn’t help other people to understand the wide range of symptoms which are part of the condition. Fatigue is not "just tiredness": they are very different experiences. Healthy people may feel “tired” if they have been doing a lot, or perhaps if they are short of sleep, but they would expect to feel better following rest and sleep. It is possible for healthy people to "push through" when they are tired. In contrast, fatigue is a much more profound experience, which is often described as exhaustion, and can also involve weakness. Some people living with M.E./CFS describe it as their "body shutting down". A particular aspect of the fatigue of M.E./CFS is known as "post exertional malaise", which is a term that means that the fatigue will tend to be worse a day or two later than the triggering activity. This is also known as "post exertional symptom exacerbation". Post exertional malaise is one of the identifying features of M.E./CFS.

What do the terms CFS and M.E. mean?