On the other hand we have a distinctive symptom in the form of PEM (ICC, CCC, SEID), which identifies patients with a common meaningful symptom which can be objectively verified via CPET.
As far as I can see — and perhaps you can double-check this yourself — I don't think it is correct to say that
physical exertion-induced PEM is a compulsory symptom that patients must have before they are diagnosed with ME/CFS under the CCC, ICC and SEID criteria.
PEM is certainly a compulsory symptom in the CCC, ICC and SEID, but it seems that under these ME/CFS definitions, if you get PEM from either physical
OR mental exertion (or both), then that is enough to satisfy the criterion for having PEM (see the extracts below copied from the CCC, ICC and SEID criteria).
So if you just have PEM induced by mental exertion (ie, cognitive fatiguability), but no PEM induced by physical exertion, then that still counts as PEM.
Thus under the CCC, ICC and SEID criteria, even if you can go jogging for miles without repercussions, you could still have ME/CFS.
This means that the notion that the 2-day CPET could be a diagnostic tool that captures all ME/CFS patients defined by the CCC, ICC and SEID criteria is probably not really correct. Certainly the CPET would be a great help in diagnosis, but it will not capture all CCC, ICC and SEID-defined ME/CFS patients.
Here are the text extracts from the CCC, ICC and SEID which relate to PEM:
The
CCC actually seems a bit ambiguous as to whether it requires both
physical AND mental-exertion induced PEM, or whether just
physical OR mental exertion-induced PEM is enough. On the one hand, the CCC says:
Post-Exertional Malaise and/or Fatigue: There is an inappropriate loss of physical AND mental stamina, rapid muscular and cognitive fatigability, post exertional malaise and/or fatigue and/or pain and a tendency for other associated symptoms within the patient’s cluster of symptoms to worsen. There is a pathologically slow recovery period usually 24 hours or longer.
But elsewhere in the CCC document it says:
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.
Under the
ICC, if you get PEM (PENE) from
physical OR mental exertion, then you satisfy the criteria for having PEM (although the ICC is also slightly ambiguous as it also says: "Low threshold of physical AND mental fatigability").
Post-Exertional Neuroimmune Exhaustion (PENE) — Compulsory
This cardinal feature is a pathological inability to produce sufficient energy on demand with prominent symptoms primarily in the neuroimmune regions. Characteristics are:
1. Marked, rapid physical AND/OR cognitive fatigability in response to exertion, which may be minimal such as activities of daily living or simple mental tasks, can be debilitating and cause a relapse.
2. Post-exertional symptom exacerbation: e.g.acute flu-like symptoms, pain and worsening of other symptoms.
3. Post-exertional exhaustion may occur immediately after activity or be delayed by hours or days.
4. Recovery period is prolonged, usually taking 24 hours or longer. A relapse can last days, weeks or longer.
5. Low threshold of physical and mental fatigability (lack of stamina) results in a substantial reduction in pre-illness activity level.
Under the
SEID criteria it is clear that you can have PEM from either
physical OR mental exertion, and satisfy the criteria for having PEM:
Post-exertional malaise (PEM)
PEM is worsening of a patient’s symptoms and function after exposure to physical OR cognitive stressors that were normally tolerated before disease onset. Subjective reports of PEM and prolonged recovery are supported by objective evidence in the scientific literature, including failure to normally reproduce exercise test results (2-day cardiopulmonary exercise test) and impaired cognitive function after exertion. There is sufficient evidence that PEM is a primary feature that helps distinguish ME/CFS (SEID) from other conditions.
In summary: if you can run a marathon without getting PEM, you can still have ME/CFS as defined by the CCC, ICC and SEID criteria (although the CCC and ICC are a little ambiguous about this).