Myalgic encephalomyelitis, abbreviated as ME, is one of several alternate names for the disease that's commonly known as chronic fatigue syndrome, or CFS. It's become common to see the abbreviations combined, as either ME/CFS or CFS/ME. The abbreviations are considered equally valid and are used interchangeably.

To understand the term myalgic encephalomyelitis, it can help to break it down into the individual medical terms.

The word myalgic is used for muscle pain and/or tenderness.

My is a shortened form of myo, which means muscle

Algic is the adjective form of algia, which means pain

The word encephalomyelitis means inflammation of the central nervous system, which is made up of the brain and the nerves of the spinal cord.

Encephalo refers to the brain

Myel means spinal cord and medulla oblongata (the brain stem)

Itis means inflammation

Why Use Myalgic Encephalomyelitis

Several countries around the world currently use the term myalgic encephalomyelitis instead of chronic fatigue syndrome, both for research purposes and when diagnosing the illness. This term appears to be gaining traction in the United States among researchers, advocates, and people with the disease, as well. Some people use the terms interchangeably, while others consider them separate conditions.

Patients, advocates, and some researchers in the U.S. have pushed for the use of ME/CFS due to the widespread belief that the name "chronic fatigue syndrome" trivializes the condition and leads to misconceptions about it. Once the public and medical community are better acquainted with the term, they plan to drop the "CFS" portion altogether and just use ME as the condition's name.

However, a major report from the Institute of Medicine has called for the name of this condition to be changed to systemic exertion intolerance disease, abbreviated as SEID.﻿﻿ That's based on the widespread abnormalities associated with the illness and, especially, one of its distinguishing symptoms—post-exertional malaise (PEM). PEM is an extreme negative reaction to exertion and an inability to repeat the same level of activity the following day.

It remains to be seen whether the name SEID will find acceptance. It faces an uphill battle since many researchers have transitioned to myalgic encephalomyelitis/chronic fatigue syndrome in their published papers.

Additionally, a lot of people with the disease have formed a strong emotional attachment to the term ME, since it was the first alternative name to gain traction that didn't involve "fatigue." A common sentiment is that the public doesn't understand the difference between clinically significant fatigue and just being tired, such as from a lack of sleep.

In this disease, the fatigue is incapacitating and unrelieved by rest, making it different from normal tiredness.﻿﻿ It has more in common with the type of exhaustion experienced with the flu or mononucleosis (a.k.a., the kissing disease).

Misconceptions With CFS

Another reason for leaving behind "chronic fatigue syndrome" is that the name has become inaccurate. The Institute of Medicine report concluded that it is a disease, not a syndrome, as is made clear in the name "systemic exertion intolerance disease."﻿﻿ A syndrome is a set of symptoms known to occur together but without an understood pathology. A disease is better understood than a syndrome. (However, the status of "syndrome" doesn't mean a condition is less serious—just that researchers don't yet know what's behind it.)

CFS has always been plagued by controversy, and the use of ME in any form is not free of it. Critics of the name myalgic encephalomyelitis and its various abbreviations say that we do not have adequate evidence of inflammation in the brain and spinal cord to re-name the disease for it. A small 2014 study published in the Journal of Nuclear Medicine did appear to provide some evidence that encephalomyelitis is a feature of the condition.﻿﻿ Still, this is just one study and we will need a lot more research to be certain that it's a consistent feature, let alone what the symptom means in the overall context of the disease.