Detailed guides to painful problems, treatments & more

Why is it always ME-slash-CFS? And where’s FM?! Myalgic encephalomyelitis vs chronic fatigue syndrome vs fibromyalgia

 •  • by Paul Ingraham
Get posts in your inbox:
Weekly nuggets of pain science news and insight, usually 100-300 words, with the occasional longer post. The blog is the “director’s commentary” on the core content of a library of major articles and books about common painful problems and popular treatments. See the blog archives or updates for the whole site.

PainSci Member Login

Submit your email to unlock this audio content (and any other stuff for members). If you can’t remember or access your registration email, please contact me. ~ Paul Ingraham, PainSci Publisher

Privacy & Security of this form This login is private and secure: the information you submit is encrypted, used only to search for matching accounts, and then discarded.

What is this two-for-one acronym with the slash: “ME/CFS”? Many people know that the CFS is for “chronic fatigue syndrome.” But only a few know that ME is for “myalgic encephalomyelitis,” fewer still can pronounce it, and hardly anyone can explain why their acronyms are always smushed together.

Or why FM for fibromyalgia doesn’t get included.

Basically, ME is the nastiest and most pathologically distinct member of the sprawling and dysfunctional CFS family. ME and CFS always get mentioned in the same breath because they are too different to completely combine into one condition, and too similar to simply separate!

But there’s nothing “basic” about any of this. (After initial publication, I added appendix to the post explaining more about why I chose to boil it down to that.) It has taken me years to slowly wrap my head around the tricky relationship between ME and CFS, but I think I can now finally express and explain it with confidence, and that is the purpose of this post. It’s not just a definition of ME, CFS, and FM, but a very carefully condensed and fine-tuned explanation of how they relate to each other.

This is an excerpt from a guide to ME/CFS that I’ve been working on. It’s the first of some highlights from that project that I will share as it evolves.

Moody B&W photo of a man holding his head in mental and/or physical pain.

This man is performing the pain of trying to find appropriate stock photography to illustrate posts about health problems like ME/CFS. (I call this image “bleak man” in my filing system.)


In theory (and officially), ME and CFS are literally the same thing. In practice, not so much, because — right or wrong — the CFS label is used much more loosely, and applied to many people who would not meet the diagnostic criteria for ME/CFS, but are definitely sick in a CFS-y way.

“Chronic fatigue syndrome” is not a diagnosis per se: it’s just a descriptive label for a pattern of symptoms dominated by fatigue, and with no obvious explanation but an incredible range of possibilities, including well understood fatiguing illnesses, as well as puzzling fatiguing illnesses that may never get a diagnosis more specific than CFS.

If CFS was a country — a crappy country you do not want to visit — then ME would be its capital city. It is much closer to being an actual diagnosis, with more severe and predictable symptoms and signs. ME is basically super CFS, a poorly understood but well-described pathological state, which often crops up in the aftermath of viral infections, with symptoms that go way beyond fatigue: severe chronic malaise, profound exercise intolerance, and mental fog as thick as being drunk. ME patients do feel fatigued, but they also feel sick.

Importantly, ME patients can actually be identified by someone other than themselves: that is, they have objective signs of disease, and not just subjective symptoms. Unfortunately, those signs are exotic biomarkers that can only be detected in a research context; there are still no clinical tests, nothing patients can ask their doctor for.

Meanwhile, ME patients have notoriously “normal” looking results for all widely available medical tests — and anything that does crop up is probably coincidental and a red herring. Pure ME simply doesn’t show up on standard medical tests. The only abnormalities that can be readily confirmed are the signs of several common health problems that are common in these patients — “comorbidities” like postural orthostatic tachycardia syndrome and irritable bowel syndrome — but their involvement is erratic and not specific to ME. They are signs of a severely distressed system.

So if ME is so different from CFS, why constantly pair it with CFS?

Not everyone with chronically fatigue illness has the hallmarks (or biomarkers) of ME, not even close. All ME is CFS, but not all CFS is ME. CFS is a category, ME is the biggest and baddest thing in that category, the most extreme and well-defined member of that club — which includes lots of members whose membership status is uncertain. Patients with undiagnosed fatiguing illnesses who eventually get a diagnosis (like cancer) get kicked out of the CFS club.

But ME patients will always belong in the CFS club. Indeed, most will be lifetime members.

And so the routine labelling of ME and CFS as a pair persists because it’s really hard to break them up. Referring only to ME would rudely leave out far too many people who have quite similar problems. But referring only to CFS would ignore the most important kind of CFS! It’s actually “politically” vital to use ME, to help emphasize the fact that a lot of CFS is definitely a distinct pathology — that’s part of how it gets taken seriously by doctors and researchers.

And so… ME/CFS.

The ME/CFS “Death Star” Venn.

And why not ME/CFS/FM, hmmm? WHY?!

Fibromyalgia is no more of a “diagnosis” than CFS is. It’s a label for a similar pattern of symptoms … but one that’s dominated by pain rather than fatigue. So it’s really just “chronic pain syndrome,” but it got it’s own weird name for historical reasons, and that makes it sound more different than it is. Many cases are not very different.

Formal diagnostic criteria also seem to separate all of these conditions, but the messy clinical reality is that fibromyalgia is often extremely similar to ME/CFS with extra pain. And ME, CFS, and FM also clearly share many symptoms and common comorbidities. For instance, fibromyalgia can include mental fog and exercise intolerance … just like ME/CFS.

And vice versa: many patients with ME/CFS also have quite a lot of pain, and would probably be considered fibromyalgia patients if the pain wasn’t so overshadowed by even worse fatigue/malaise.

Although they can be quite different, they can also be very similar. And so fibromyalgia seems an awful lot like a sibling to ME/CFS — but you never see “ME/CFS/FM.” Whyever not? Because they do have distinct diagnostic criteria, officially. But the overlap is so substantial that I do always group them together in my head. I won’t catch on, but it’s always going to be “ME/CFS/FM” to me.

And then there's long COVID…

I actively follow long COVID news, which is a great cure for any pesky optimism you may have somehow managed to hang onto over the last few years. If you really want to feel well-informed but extremely depressed and enraged, I have just the thing for you: the horrifying STAT exposé of the NIH’s criminally incompetent failure to study long COVID over the last two years, with a billion-dollar budget — not just “nothing to show” for it, but literally worse than nothing. 😡

Long COVID is directly relevant to ME, CFS, and FM. It’s not a twin, but the resemblance is striking.

However, “ME/CFS/FM/LC” would be a bit ridiculous.

Appendix: An explanation of why I chose to describe CFS as something different from ME/CFS

When I first published thispost, I got a few complaints about how I defined ME as a subset of CFS (and how strongly I equated ME/CFS and FM). While this wasn't really a surprise — it’s a perpetually controversial topic — I was concerned, and it inspired substantial introspection, and some edits. Although I had already thought long and hard about it, I continued. I didn't conclude that my strategy was wrong, but I did realize that I probably hadn't explained it well enough. So, here’s some elaboration on why I’ve chosen to explain this the way that I have in this document.

Basically, I’ve prioritized “practice” over “theory.”

ME and CFS are both used to describe the same patients, but there’s been a great deal of controversy over that, because of the trivializing focus on “fatigue” in “chronic fatigue syndrome.” And so officially there’s no difference between ME and CFS. And what’s official about it is that there are diagnostic criteria for ME/CFS, and there are no there are no special diagnostic criteria for ME as distinct from CFS. We just have diagnostic criteria for a disease that gets labelled with both names. Anyone who meets those criteria is perfectly welcome to identify as a person suffering from either ME or CFS, and they are not wrong. As I wrote, “All ME is CFS.”

But a great deal of CFS-ish illness — like my own, which is probably relevant here! — does not fit the diagnostic criteria for ME/CFS! Ruh roh.

Consequently, there is extremely widespread informal use of the term CFS to label people who do not meet the diagnostic criteria for ME/CFS — the infamous “wastebasket diagnosis,” applied to people with some other undiagnosed “fatiguing illnesses.” This category is extremely contentious and conceptually difficult and many people have argued very forcefully that it needs to go away. If only wishing (or pounding the table) could make it so! Language prescriptivism is largely futile, and CFS is too descriptive and generic to ever go away. It’s only a “wastebasket” diagnosis if it’s clinically abused (as it often is, but railing against the TERM is not going to fix that much larger problem).

So the defacto reality that I chose to describe is that ME means only one thing: a really nasty illness with well-established diagnostic criteria. But “CFS” means both that … aaaand a whole bunch of other stuff: it refers to people who do not meet the diagnostic criteria for ME, often because their symptoms are much milder, and their brains aren’t inflamed, etc.

This isn’t necessarily right. But it’s certainly not carelessly expressed. I am well aware of the controversies about the terminology. For instance, I know that some experts (perhaps most notably Jodi Bassett) have argued very forcefully that “CFS” should never be used to describe anyone ever again. I respect that opinion, but I do not agree with it.