Then why does NICE spend all this effort developing guidelines, including those for people who have "ME/CFS"? How do they decide who should be treated by the ME/CFS guidelines if they don't have some 'features" by which to identify the disease?
As I explained above there are certainly features of the disease, just as there are features of arctic redpolls. But you have to use these features
intelligently to come to a decision as to whether or not someone is usefully labelled as having ME/CFS or probable ME/CFS or possible ME/CFS.
The research literature is supposed to provide evidence of treatment efficacy for well defined cohorts. Doctors are then again expected to extrapolate intelligently from these cohorts to individual cases based on what they think are the probabilities of them being representative of that cohort. It is all a matter of intelligent inference of probabilities. Most of the time we do that unconsciously, whether treating patients or identifying birds or buying tomatoes or whatever. The human brain makes useful decisions based oral sorts of contextual information.
The problem with the Fukuda based guidance here - and as far as I can tell, the NICE guidelines - is that they are little more than a wastebin into which to put medically unexplained fatigue and that does a disservice to everyone.
What the NICE guidelines gives is a broad list of features that should make the physician consider the diagnosis. If the physician is experienced in the condition they can then use their intelligence to decide. If not the list provides a useful screen for people that would be suitable to refer on to a specialist with a query of a diagnosis. It would be entirely wrong to suggest that doctors use the guidelines alone to make a diagnosis. It would be as irresponsible as suggesting that you start driving a car just by reading the manual. You have to learn the practicalities.
And the guidelines have to cover a broad range because people who have chronic fatigue but not necessarily ME have to be covered by some sort of guideline and the GP has to know roughly where to look for both types of patient. So the guidelines have to have a broad remit. They are a practical guide for doctors in real life.
Regarding why I raised this originally - I was just looking for a link to a study that reported different rates of prevalence by Oxford, Nice, and Fukuda for something I am working on.
The best I can think of is the Nacul study but I don't know whether criteria they looked at. I don't think they did 'NICE criteria' because I don't think such a thing actually exists. It would have to be a population study not a clinic study because clinics only take a skewed referral cohort.
Regarding PACE - the use of non-specific cohort selection methods that don't require core features of the disease is also a problem.
I am not sure that it matters. If you set up an uninterpretable study you cannot interpret it for whatever group you recruit.
I agree that if a decent study was set up it might be good to narrow down the cohort, but this is not necessarily true. The reason why not specifying PEM is a specific problem is that it can lead to recruitment bias for studies of exercise. That is a pretty subtle problem. I think it confuses the issues around NICE guideline review. Treatment studies are not necessarily best restricted to specific diagnoses. I have run trial with wider recruitment and for good reason.
Regarding "it makes sense to be extra careful with exercise with people with PEM but everyone gets that" - Unfortunately, lots of people, including in the medical community don't get that. That's one of the reasons that I think its so important to have an accurate definition of PEM and provide guidance to medical providers on how to recognize PEM and the implications of PEM for clinical management plans.
The problem with this is that if we say it is important to define PEM so that people with PEM are screened out from GET then it is all too easy for GET to be included in
the wider remit that the guideline has to have for other cases of chronic fatigue. We have to go with the realities. If GET is included at all then inevitably it will end up being used the way it is now. From my perspective the only sensible plan is go with the real evidence - which is that there is no reason to recommend GET in any situation. So although exercise intolerance is worth documenting and building into advice to individuals it is not sold as the arbiter of whether people get exercises.
In other words the two key things that need to go into NICE guidelines are strict adherence to evidence and pragmatically. We have to have something that doctors can use. We also need to make sure that a desire for tidiness does not end up having the opposite effect to that hope for.