My mother had mild cognitive impairment for a long time before the onset of Alzheimer's so I do know a little about all that. Her MCI (so classic that they were pursuing her for studies) was nothing whatsoever like brainfog.
The whole idea being discussed in this thread (even if Dr Myhill isn't actually saying precisely that brain fog leads to dementia) makes no sense to me either. I'd want to see some very good evidence for any such link before considering this idea seriously.
I do think that this kind of suggestion is obviously bound to cause the same kind of fears in patients with brainfog that clairelou suggests. Really, what purpose does it serve to worry people with brainfog with the idea that they might have something horrible like this ahead of them? It's a distressing concept, it's surely not going to help patients to be worried about this, and even if there was evidence to suggest this, one would have to think twice before telling patients this and be very careful to word things cautiously and explain the probabilities carefully. Clearly that hasn't happened here, given how clairelou has read this. So it looks as though this part of Dr Myhill's site really needs a rethink.
Before we throw Dr Myhill under the bus, though, I do want to note some context. Her career as a physician, as I understand it, was transformed when she started seeing lots of patients (farmers, mostly) turning up with what she concluded was organophosphate poisoning from sheep-dip, causing symptoms very similar to ME/CFS (though perhaps a little closer to Gulf War Illness). There were so many of these patients that she ended up making this whole area effectively her life's work. But there were no sanctioned therapeutic approaches available to her, and no recognition of the poisoning, and indeed vigorous denial from the authorities and pursuit of her as a 'quack' for the things she said. So she forged her own path, and pursued a lot of ideas that were well off the beaten track, treated these patients as best she could, and observed what worked. Only in the last year or two has it been revealed that the government was lying about sheepdip all the way through, ever since the 1980s, and the evidence has come to light that the authorities knew damn well what was going on, and covered it up - and Dr Myhill and the Countess of Mar were right.
I think that kind of history is bound to radicalise a person, and I have immense admiration for Dr Myhill's bravery and dogged determination in sticking to her guns throughout the last few decades. Any trained physician has much easier and more comfortable routes to choose, which would make them a lot more money too. I also put my own recovery largely down to advice received from another physician following her principles (a work colleague who was also helped massively by her put me onto this). I don't actually think I would be here on Phoenix Rising now if it were not for Dr Myhill, because I was so ill before I found her advice. So I find it hard to hear criticism of her without balancing that out with the positives, and I think when we critique specific aspects of someone's work that seems "out there", and which may well be flat wrong, we should also be careful to add some balance and look at the rest of someone's work, and acknowledge the good things they have done.