Hip
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Modern ME/CFS diagnostic criteria require post-exertional malaise (PEM) as a mandatory symptom for an ME/CFS diagnosis. PEM of course is the well-known temporary period of worsened ME/CFS symptoms that usually hit in the next day or two after engaging in exertion (but may also appear on the same day, or even immediately after exertion).
Thus on ME/CFS forums we often see it said that "if you do not have PEM, you do not have ME/CFS".
But we should be mindful that PEM may be triggered either by physical exertion, and/or by cognitive, mental or emotional exertion.
This means that if a patient has all the usual ME/CFS symptoms, but they do not get PEM after physical exertion, they may still qualify for an ME/CFS diagnosis, provided they experience PEM after cognitive, mental or emotional exertion.
So for example, if someone finds that cognitive activity such as reading for some time, performing arithmetic, doing their home accounts, engaging in lengthy conversation, etc, later triggers a period of worsened ME/CFS symptoms (such as worsened brain fog, worsened fatigue, malaise, worsened sound sensitivity, or any other worsened ME/CFS symptoms), then I believe that would count as PEM.
Likewise, if someone finds that being involved in stressful or emotional activity triggers a period of worsened ME/CFS symptoms, that also counts as PEM.
When seasoned ME/CFS patients chat with brand new patients who are wondering whether they may have ME/CFS, these new patients are often asked if they have PEM. And if they reply that they do not get PEM after physical exertion, then they may be told that the possibility of having ME/CFS is in doubt.
However, it's important to check not just whether new patients have physical exertion-triggered PEM, but also whether they might have cognitive, mental or emotional exertion-triggered PEM. Because either counts as having PEM.
If you do not experience physical exertion-induced PEM, but do get cognitive, mental or emotional exertion-induced PEM, you still have PEM.
The Canadian consensus criteria (see page 4) make this clear:
And the IOM criteria also make this clear:
Fatigue, Rapid Fatigability and PEM in ME/CFS Diagnostic Criteria
It may be worth reviewing these three cardinal ME/CFS symptoms, so that we understand them. In some ME/CFS diagnostic criteria, such as the Canadian consensus criteria, all three must be present for an ME/CFS diagnosis. Other diagnostic criteria are less strict.
All these three symptoms also come in two forms: the physical form and the mental form.
Fatigue
Physical fatigue involves feeling physically drained or weak. Physical fatigue is characterised by difficulties in performing physical activities, due to lack of muscular strength or lack of physical energy.
Mental fatigue or mental exhaustion involves feeling mentally weary, frayed or drowsy. Mental fatigue is characterized by difficulties concentrating and performing cognitive tasks (such as reading, arithmetic, filling in forms, talking to people, etc).
Rapid Fatigability
Rapid physical fatigability (poor physical stamina) is a muscular fatigability that quickly appears during physical exertion, such that the longer the exertion goes on, the weaker the muscles feel. This muscle weakening can occur fast, within a minute of starting a physical exertion.
Rapid mental fatigability (poor mental stamina) is a fatigability of mind that quickly appears when performing mental or cognitive tasks (tasks which quickly exhaust you mentally might include reading, arithmetic, filling in forms, talking to people, etc).
PEM
Physical exertion-induced PEM is where physical exertion or physical exercise triggers a temporary period of worsened ME/CFS symptoms (and during this period, flu-like symptoms or pain may also appear).
Mental exertion-induced PEM is where cognitive or emotional exertion, or sometimes just sensory overload (light and sound), triggers a temporary period of worsened ME/CFS symptoms (and during this period, flu-like symptoms or pain may also appear).
IOM Criteria Requirements
The IOM criteria require ongoing fatigue to be present for an ME/CFS diagnosis, but do not distinguish between physical fatigue and mental fatigue, so presumably either (or both) are acceptable. The IOM criteria require PEM to be present, but do not distinguish between physical exertion-induced PEM and mental exertion-induced PEM, so presumably either (or both) are acceptable.
Canadian Consensus Criteria Requirements
The CCC criteria require ongoing physical fatigue as well as ongoing mental fatigue to be both present for an ME/CFS diagnosis. The CCC also requires the presence of both rapid physical fatigability as well as rapid mental fatigability. But the CCC will accept either physical exertion-induced PEM or mental exertion-induced PEM as satisfying PEM criterion.
International Consensus Criteria Requirements
The ICC criteria do not require either ongoing physical fatigue or ongoing mental fatigue to be present for an ME/CFS diagnosis. The ICC requires rapid fatigability to be present, but will accept either rapid physical fatigability or rapid mental fatigability. The ICC requires PEM to be present, but will accept either physical exertion-induced PEM or mental exertion-induced PEM.
So the ICC are not as strict as the CCC when it comes to fatigue, fatigability and PEM requirements.
Thus on ME/CFS forums we often see it said that "if you do not have PEM, you do not have ME/CFS".
But we should be mindful that PEM may be triggered either by physical exertion, and/or by cognitive, mental or emotional exertion.
This means that if a patient has all the usual ME/CFS symptoms, but they do not get PEM after physical exertion, they may still qualify for an ME/CFS diagnosis, provided they experience PEM after cognitive, mental or emotional exertion.
So for example, if someone finds that cognitive activity such as reading for some time, performing arithmetic, doing their home accounts, engaging in lengthy conversation, etc, later triggers a period of worsened ME/CFS symptoms (such as worsened brain fog, worsened fatigue, malaise, worsened sound sensitivity, or any other worsened ME/CFS symptoms), then I believe that would count as PEM.
Likewise, if someone finds that being involved in stressful or emotional activity triggers a period of worsened ME/CFS symptoms, that also counts as PEM.
When seasoned ME/CFS patients chat with brand new patients who are wondering whether they may have ME/CFS, these new patients are often asked if they have PEM. And if they reply that they do not get PEM after physical exertion, then they may be told that the possibility of having ME/CFS is in doubt.
However, it's important to check not just whether new patients have physical exertion-triggered PEM, but also whether they might have cognitive, mental or emotional exertion-triggered PEM. Because either counts as having PEM.
If you do not experience physical exertion-induced PEM, but do get cognitive, mental or emotional exertion-induced PEM, you still have PEM.
The Canadian consensus criteria (see page 4) make this clear:
Post-Exertional Malaise and/or Fatigue: Physical or mental exertion often causes debilitating malaise and/or fatigue, generalized pain, deterioration of cognitive functions, and worsening of other symptoms that may occur immediately after activity or be delayed.
And the IOM criteria also make this clear:
Post-exertional malaise (PEM) — worsening of symptoms after physical, mental, or emotional exertion that would not have caused a problem before the illness.
Fatigue, Rapid Fatigability and PEM in ME/CFS Diagnostic Criteria
It may be worth reviewing these three cardinal ME/CFS symptoms, so that we understand them. In some ME/CFS diagnostic criteria, such as the Canadian consensus criteria, all three must be present for an ME/CFS diagnosis. Other diagnostic criteria are less strict.
All these three symptoms also come in two forms: the physical form and the mental form.
Fatigue
Physical fatigue involves feeling physically drained or weak. Physical fatigue is characterised by difficulties in performing physical activities, due to lack of muscular strength or lack of physical energy.
Mental fatigue or mental exhaustion involves feeling mentally weary, frayed or drowsy. Mental fatigue is characterized by difficulties concentrating and performing cognitive tasks (such as reading, arithmetic, filling in forms, talking to people, etc).
Rapid Fatigability
Rapid physical fatigability (poor physical stamina) is a muscular fatigability that quickly appears during physical exertion, such that the longer the exertion goes on, the weaker the muscles feel. This muscle weakening can occur fast, within a minute of starting a physical exertion.
Rapid mental fatigability (poor mental stamina) is a fatigability of mind that quickly appears when performing mental or cognitive tasks (tasks which quickly exhaust you mentally might include reading, arithmetic, filling in forms, talking to people, etc).
PEM
Physical exertion-induced PEM is where physical exertion or physical exercise triggers a temporary period of worsened ME/CFS symptoms (and during this period, flu-like symptoms or pain may also appear).
Mental exertion-induced PEM is where cognitive or emotional exertion, or sometimes just sensory overload (light and sound), triggers a temporary period of worsened ME/CFS symptoms (and during this period, flu-like symptoms or pain may also appear).
IOM Criteria Requirements
The IOM criteria require ongoing fatigue to be present for an ME/CFS diagnosis, but do not distinguish between physical fatigue and mental fatigue, so presumably either (or both) are acceptable. The IOM criteria require PEM to be present, but do not distinguish between physical exertion-induced PEM and mental exertion-induced PEM, so presumably either (or both) are acceptable.
Canadian Consensus Criteria Requirements
The CCC criteria require ongoing physical fatigue as well as ongoing mental fatigue to be both present for an ME/CFS diagnosis. The CCC also requires the presence of both rapid physical fatigability as well as rapid mental fatigability. But the CCC will accept either physical exertion-induced PEM or mental exertion-induced PEM as satisfying PEM criterion.
International Consensus Criteria Requirements
The ICC criteria do not require either ongoing physical fatigue or ongoing mental fatigue to be present for an ME/CFS diagnosis. The ICC requires rapid fatigability to be present, but will accept either rapid physical fatigability or rapid mental fatigability. The ICC requires PEM to be present, but will accept either physical exertion-induced PEM or mental exertion-induced PEM.
So the ICC are not as strict as the CCC when it comes to fatigue, fatigability and PEM requirements.
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