Disease vs. Syndrome in Fibromyalgia and ME/CFS

Among the many confusing things you encounter when learning about fibromyalgia syndrome (FMS) and chronic fatigue syndrome (CFS or ME/CFS) is the difference between a disease and a syndrome.

The word "syndrome" has been so misused in the popular media that it carries a connotation of being made up, silly, or overblown. Meanwhile, "disease" sounds ominous and scary. It's common for people who don't believe in these conditions to dismissively say they are not really "diseases." That leads some people to believe that they're not "real."

The classification, though, has no bearing on whether they exist or how serious they are. It's simply a matter of how well they're understood.

And here's something that muddies the waters: FMS and ME/CFS are very similar, yet fibromyalgia is still classified as a syndrome, while ME/CFS (which has the word "syndrome" in its name) is officially recognized as a disease.

So what's the difference?

Doctor showing digital tablet to patient
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The definition of syndrome is pretty straight forward: a collection of signs and symptoms known to frequently appear together.

We're learning more about the various physiological problems associated with FMS—such as neurotransmitter dysregulation and immune system irregularities—but so far, researchers have not uncovered the underlying cause (or causes) of these problems. This is one reason FMS isn't classified as a disease. However, as we gain more knowledge, we're likely getting closer to re-classification.


Defining disease is a little more complicated. Some medical dictionaries define it as a disorder in a system or organ that affects the body's function. That's not very helpful, because with FMS, we can point to multiple disorders in systems and organs that affect our bodies. Other medical dictionaries offer a clearer distinction:

    • A morbid entity characterized usually by at least two of these criteria:
      recognized etiologic agent (cause)
    • identifiable group of signs and symptoms
    • consistent anatomic alterations

On top of not knowing the causes of FMS, signs, and symptoms are too variable and often point to numerous possible causes, and researchers have failed to find anatomic alterations that are consistent enough to stand up to scientific scrutiny.

The same can be said of ME/CFS, yet that's classified as a disease. It, however, was fortunate enough to have a government panel go over extensive evidence that was convincing enough for the disease designation. Something similar hasn't happened with FMS.

To Further the Confusion

Something that may compound the confusion about the difference between disease and syndrome is that a name containing the word syndrome may stick even after the illness becomes classified as a disease. Even if the medical community changes the name, the old one can continue in popular usage.

ME/CFS is an example of this. Along with its official recognition as a disease came the suggested name of systemic exertion intolerance disease, or SEID. That name, however, has failed to catch on with patients, advocates, or the medical community, so we're still using a name that contains "syndrome." 

In addition to ME/CFS, we've got AIDS—acquired immunodeficiency syndrome. Scientists figured out what causes it years ago and usually call it HIV disease, yet the name AIDS persists in common usage.

Living With a Syndrome

It's important to remember that while the term "syndrome" sometimes seems to belittle the illness, it's really just a classification, based in part on what the medical establishment understands about it. When someone throws out that "it's just a syndrome" argument, they should take a close look at what they're really saying. It doesn't mean your illness is less real or serious than a disease; it means it's less understood.

For those of us with a syndrome, it often means our doctors don't know much about them and effective treatments can be hard to find. Some of us would probably be happy to swap for a disease if it meant an easier road to symptom management as well as being taken more seriously.

Those of us with FMS and ME/CFS frequently have other syndromes, too, including:

So when someone says to you, "Oh, that's just a syndrome," maybe you can remind them that's what the S in AIDS stands for. Then you can add, "AIDS became classified as a disease once scientists figured it out, and so did ME/CFS—so it's just a matter of time before FMS (and MPS, and RLS, and IBS) is called a disease, too."

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