well, but the symptoms are all over the place. Some are seizures of various kinds, some are motor paralysis or weakness, some are sensory (hysterical blindness/deafness), others are cognitive (memory, concentration, "brain fog," etc. It sure seems like a jumbled collection of symptoms rather than a specific set.
No, David, the symptoms fall into a specific category: abnormal movements, paralysis, sensory loss, blindness and seizure type movements all suggestive of local neurological lesions but nearly always without any possible interpretation in terms of a known structural lesion no structural lesion is detected. They tend to be stereotyped. As a trainee you doubt these people exist until you come across them in A/E with what it says in the books. That is the category. Cognitive things like brain fog are not part of the definition of FND. If some people complain of these as well that is secondary. The extension of FND to things like ME/CFS is something else - completely inappropriate.
The evidence for brain dysfunctions seems to be both absence of evident structural damage and fMRI associations,
No, the evidence of dysfunction is simply that there are symptoms or signs of dysfunction. The MRI studies are about proving theories in research. In the patients the dysfunction is having a left arm flailing about when there is no reason for it to. There must be some dysfunction in the brain since movements of that sort are controlled by central grey matter in the brain. The theories of people like Mark Edward are wrong but they are not what defines the clinical diagnostic category.
which lead to declarative statements that all FND, including unexplained cognitive deficits, is related to subtle changes in the brain.
But cognitive deficits are obviously due to subtle changes in the brain. They aren't due to the liver!
I am not arguing about the idiocy of these declarative statements. I am pointing out that there is a group of people who share a clinical problem that needs to be called something. I don't like FND, but some of them do and it is mean for others to deny them the reality of their diagnosis if they have nothing better on offer.
Some of the people put in this category will be misdiagnosed and turn out to have supra nuclear palsy or MS. But that is a different issue.
And the treatments are always CBT and some form of physio based on distracting people from the symptoms.
Actually they aren't. I have at times shared care of people with this sort of problem with colleagues at the national Hospital for Nervous Diseases and taken part of multidisciplinary meetings. The discussion at those meetings was often as sensible and open-minded as the discussion here. Everyone admitted that they had no idea what was going on or quite what to do and plans were developed largely as damage limitation exercises to try to find a way of seeing someone through a period of illness none of us understood. I agree that these days a lot of people seem to be getting this wrong, but again that is another issue.
I'm sure there are people who fall into that category, but how can anyone know for sure who they are?
You rarely know anything for sure in medicine, but the situation here is the same as any other. Skilled assessment tends to get things right. In neurology it pays to be obsessive. But there is always a level of uncertainty. Again, this is another issue.
The FND people say a third of patients attending neurology clinics have FND.
But those are just the empty cans making most noise. None of the physicians I know would take that seriously. Unfortunately everything is now done by soundbite, including the medical journals.
So anything not directly tied to structural damage gets defined as FND.
No, that isn't how it is defined. Schizophrenia is not tied to structural change and nobody calls it FND, nor migraine as far as I know. FND specifically relates to a clinical pattern that shows some signs that it ought to be related to a specific localised abnormality but that lesion is not identified at the relevant level. So a seizure ought to be related to an EEG focus or a spot on MRI and in FND it isn't. In Parkinson's the clinical picture is known to be associated with a biochemical change in the substantial nigra that you may only be able to see at autopsy so it is not FND because there is no discordance in findings. Discordance in findings is central to the concept of FDN and I don't think it is unreasonable to think it likely that that discordance occurs in 'higher' brain function in cortex, but that is a million miles away from being 'psychological' in the 'psychosomatic' sense.
In your view, are we talking about a very small percentage of these patients? Or do you think it's really as widespread at the Jon Stones and Alan Carsons make it out to be?
The clinic data are irrelevant for all sorts of reasons to do with triage and ascertainment. I suspect that people who can reasonably be classed as having FND form about 0.05% of the population. They may fill Jon Stone's clinics because he asks for them. I looked after about 1000 people on a regular basis at any one time as a physician. If FND as I understand it occurred in more than 0.1% I should have seen cases as coincidental comorbidities in my patients. I maybe saw one every five years, if that.