I don't know of a comparison of people with ME w/POTS(other forms of OI) and people with ME who do not have any form of OI. It'd also be interesting to see how people with OI but without ME do on the 2-day CPET - especially since some clinicians think OI includes PEM (I do not know how stringently they were characterizing PEM).
I don't but such a study would be extremely interesting. From lurking around a few POTS forums I get the impression that there are three groups of POTS patients with regard to exercise: 1) The first group finds exercise beneficial. They may have to do so horizontally but a brisk ride on the recumbent bicycle makes them feel better. 2) The second group complains of exercise intolerance or post-exertional fatigue. 3) And the third group, while not using the actual term PEM, describe symptoms that sound very much like PEM. This last group is the most interesting. Are they just misdiagnosed and actually have ME? Or is there a subgroup of 'pure' POTS patients that actually experience PEM? In which case PEM wouldn't be unique to ME.
I agree this would be an interesting question, along with measuring OI specific symptoms post exertion. Personally, I only experience OI after substantial exertion (for me), but it occurs sooner than the rest of the post exertional exacerbation.
