Research

PEM – ME’s gift to the medical world

Cort Johnson from the Health Rising blog explores how this core symptom of ME/CFS was first introduced and the essential role it now plays in defining the disease.

The term post-exertional malaise, or PEM, is where the past and the future meet in ME/CFS.

The disease’s inability to fit into known medical paradigms, and its attempts to break free of confining contexts and to open up new understandings, all come together in what is probably the essential term in ME/CFS. The term PEM truly carries within it worlds.

PEM refers to the dramatic exacerbation of symptoms that too much exertion produces in people with ME/CFS.

A new symptom

It’s not clear when the term was first coined, but it’s very clear that the term is ME/CFS born and bred. A PubMed search reveals that the first appearance of the term occurred in an article, “Signs and Symptoms of Chronic Fatigue Syndrome”, that appeared in the January 1991 supplement of the Review of Infectious Diseases. Since then, the term has appeared in hundreds of studies, virtually all of which, until the emergence of long COVID, referred to ME/CFS.

The entrance of a new symptom into the modern medical lexicon is truly a remarkable thing. The fact that the term needed to be born to satisfactorily explain ME/CFS speaks volumes of how unusual a disease it is, and reveals one reason the medical system has such trouble coping with it.

Exertion – particularly physical exertion – is almost universally accepted as a helpful activity. Even people whose core muscle of exertion, their heart, has been damaged are encouraged to exercise. People who have trouble breathing – another critical component of exertion – are encouraged to exercise. People with arthritis – who can’t move their joints without pain – are asked to exercise.

It seems that there’s no chronic illness where exercise is not called for – until you come to ME/CFS.

Exercise vs exertion

With ME/CFS we enter into a different world entirely. Exercise – a vigorous activity that gets the heart pounding and the body producing a nice sweat – no longer applies. Now the focus is on the much milder and less cardiovascular-challenging term “exertion”, but even exertion has to be redefined.

All sorts of activities, such as walking, washing the dishes and showering, now count as exertion, and potentially disabling exertion at that. In what other disease does showering count as a potentially disabling form of exertion?

Yet another problem lurked. Even as the term PEM helped distinguish ME/CFS from “fatigue”, it carried with it dangerous seeds of the past. Medline Plus describes “malaise” as being “a general feeling of discomfort, illness, or lack of well-being” that often occurs with fatigue and is distinguished by “a feeling of not having enough energy to do your usual activities”. (Ironically, Medline does not include ME/CFS as one of the many diseases in which malaise may be present.)

Just as “fatigue” describes nothing of the exhaustion and depletion that often accompanies ME/CFS, so the term “malaise” hardly describes the dramatic exacerbations of pain, cognitive problems, sensory issues and other symptoms that accompany too much exertion.

The term has stuck, however, and over time has become the central distinguishing feature of ME/CFS.

In a remarkable transition, the UK has gone from dismissing PEM entirely (in the Oxford Definition) to – in the new NICE guideline – featuring it in two of the four symptoms they consider to be core to this disease. NICE now considers that a person with ME/CFS must present “debilitating fatigue that is worsened by activity”, and post-exertional malaise that is disproportionate to the activity undertaken, which can take days to fully manifest itself, and take hours, days or weeks to go away. 

Once again, it’s been up to ME/CFS researchers to make real the invisible, and document the existence and biological roots of PEM – and so they have.

PEM research

Studies using two-day cardiopulmonary exercise tests championed by the exercise physiologists at the Workwell Foundation indicate – in what thus far is a unique finding in medicine – that a short bout of maximal exertion one day impairs an ME/CFS patient’s ability to produce energy the next.

To get a handle on just how unusual a response that is, consider that people with all sorts of very serious diseases (heart failurepulmonary hypertensioncystic fibrosismild-to-moderate COPD and stroke) can jump on a bike and exercise to exhaustion one day, and then hop on the bike again the next day and generate the same amount of energy. For reasons that are still unclear, people with ME/CFS can’t.

This recognition has led to another unusual development in the ME/CFS field – the use of an exercise stressor in studies to better understand the disease.

Studies have found that short bouts of strenuous exercise produce a host of negative biological effects in ME/CFS, including alterations in energy production and lipid pathwaysincreased blood lactate levelsproblems opening the blood vesselsleaky gut, reducing parasympathetic nervous system functioningincreased oxidative stressincreased default mode network activitycognitive deterioration and disrupted circadian rhythms.

What next?

PEM has therefore been shown to be real both symptomatically and biologically. The big question is: what’s next for this paradigm-busting term?

The creation of the term PEM was both inevitable and essential. It was inevitable because something like it had to be created in order to properly describe ME/CFS, and it was essential because it let the world know that ME/CFS is something more than a fatiguing disorder. 

Some 30 years or so after ME/CFS introduced the term to the medical field, PEM may matter more than ever. It’s not clear in what other diseases PEM – as opposed to fatigue – plays a major role, but it’s hard to believe that it’s restricted to ME/CFS.

Right now, long COVID – where PEM has been featured in at least ten papers – has been the largest recipient of the ME/CFS community’s gift, but it’s not likely to stop there. Hints of PEM have shown up in other exercise-challenged conditions such as postural orthostatic intolerance syndromeGulf War illnesspost-treatment Lyme diseasefibromyalgia and rheumatoid arthritis.

The term PEM is forcing the medical community to grapple with new and challenging ideas of disease. You could call it ME/CFS’s gift to the medical world.