The case against the ‘S’: Is functional neurological disorder(s) one condition or many? 2026 Palmer et al

[Andy]

Abstract​

Functional neurological disorder (FND) is one of the most common, but least researched, conditions in neurology. It can cause a broad range of sensory, motor, and constitutional symptoms, with the underlying mechanism of symptom-generation proposed to be an abnormality of perceptual inference. Debate exists as to whether the clinical entity referred to as FND is truly a single disorder or is in fact multiple entities which have been erroneously amalgamated into the same condition. We sought to provide empirical evidence on this question by treating it as a problem of model comparison. We formulated statistical models equivalent to: (1) FND being a single entity with variation in phenotype, represented by latent trait models, and (2) FND being multiple discrete entities, represented by latent class models. We fitted these models to data on the symptoms experienced by 697 people with FND from the FND Research Connect database (www.fnd-research.org) and used Bayesian model comparison to compare their likelihoods. All but one of the latent trait models, representing FND as a single entity with heterogeneous phenotype, fit the data better than all the latent class models. Furthermore, secondary analysis of the latent class models showed results compatible with the models discretising continuous variation rather than capturing true discrete categories. Our results are most compatible with the hypothesis that the symptom structure of FND is the result of a single pathophysiological process, either as a single entity, or a common pathway preceded by multiple causative processes where the common pathway is solely responsible for the phenotype.

Open access

 

[Andy]

Functional neurological disorder (FND) is among the most common conditions encountered in neurological practice (Finkelstein et al., 2024). It can cause a broad range of symptoms, including seizure-like attacks (functional seizures), paralysis, involuntary movements, disruption of both somatosensation and the special senses, cognitive difficulties, and constitutional symptoms such as fatigue and dissociation.

...

Part of Table 1. Participant demographics.

Clinician-diagnosed comorbidities (%)
Epilepsy	2.9
Depression	60.2
Anxiety	69.0
Migraine	45.3
ADHD	19.8
Autism spectrum disorder	10.1
Dyslexia	6.8
Borderline personality disorder	7.5
Parkinson's Disease	0.6
Irritable bowel syndrome	25.9
Fibromyalgia	22.4
Chronic regional pain syndrome	8.6
Ehlers-Danlos syndrome	3.4
ME/CFS	19.4
Inducible laryngeal obstruction	4.3
Globus pharyngeus	1.9
Mast cell activation syndrome	2.0

 

[Felis Catus]

Our results are most compatible with the hypothesis that the symptom structure of FND is the result of a single pathophysiological process, either as a single entity, or a common pathway preceded by multiple causative processes where the common pathway is solely responsible for the phenotype.

Yes, it's called ignorance.

 

[Jonathan Edwards]

Yes, it's called ignorance.

I am not sure that ignorance can be considered a pathological process.

But wilful ignorance certainly could.

 

[rvallee]

There are many conceptual flaws in this opinion piece. It opens by its own argument, framing FND as one single thing, which is what it tries to argue, and is also a common opinion anyway, but it assumes it in arguing for it. Good grief.

It can cause a broad range of sensory, motor, and constitutional symptoms

There is no established cause-and-effect here, the symptoms are what get labelled as 'functional', based entirely on not finding specific pathology to explain them, which is a common thing since medical technology is still very primitive. The concept of FND therefore does not 'cause' any of this.

These symptoms are thought to be generated by sensory predictions of abnormal function

And they admit to having no actual mechanism that can 'cause' those things. All of this is purely assertive speculation, allowed simply because no evidence is required here, this is a grandfathered concept that is given a free pass on everything, ye olde mythical conversion disorder, which is the true "one root thing" here. They won't argue this, but this is it. It's always a big tell when everyone thinks it but don't dare say it.

Reading the rhetorical argumentation, this reminds me very strongly of political science theory. Except less smart, somehow. They're just schools of thought, various opinions about things simply because some of the underlying facts are not measurable, combined with differences of perspectives. None of this is scientific, it's barely pop philosophy.

The data are very superficial, a simple binary yes/no, and there doesn't seem to be a time dimension. The early patient-led LC research was miles better than this, although this isn't just a problem with the functional ideologues, this is also generally true of almost all LC research. Researching internal models of reality never works, especially when those models are themselves a rejection of reality. What an absurd disaster this ideology is.

 

[bobbler]

There are many conceptual flaws in this opinion piece. It opens by its own argument, framing FND as one single thing, which is what it tries to argue, and is also a common opinion anyway, but it assumes it in arguing for it. Good grief.

There is no established cause-and-effect here, the symptoms are what get labelled as 'functional', based entirely on not finding specific pathology to explain them, which is a common thing since medical technology is still very primitive. The concept of FND therefore does not 'cause' any of this.

And they admit to having no actual mechanism that can 'cause' those things. All of this is purely assertive speculation, allowed simply because no evidence is required here, this is a grandfathered concept that is given a free pass on everything, ye olde mythical conversion disorder, which is the true "one root thing" here. They won't argue this, but this is it. It's always a big tell when everyone thinks it but don't dare say it.

Reading the rhetorical argumentation, this reminds me very strongly of political science theory. Except less smart, somehow. They're just schools of thought, various opinions about things simply because some of the underlying facts are not measurable, combined with differences of perspectives. None of this is scientific, it's barely pop philosophy.

The data are very superficial, a simple binary yes/no, and there doesn't seem to be a time dimension. The early patient-led LC research was miles better than this, although this isn't just a problem with the functional ideologues, this is also generally true of almost all LC research. Researching internal models of reality never works, especially when those models are themselves a rejection of reality. What an absurd disaster this ideology is.

Ah everything about FND methods relies on circular ‘validity checks’ . The diagnosis works because those diagnosed are checked by the same thing that put them in that pile.

The ones who turned out to have CJD or Parkinson’s might have died with very little chance to get support for those or affairs in order but ‘the FND diagnosis was essential according to the FND authors’ and not a misdiagnosis but it’s like when you can cross-examine a witness because they died yet worse because the person writing about them was a fan of the giving them the FND diagnosis in the first place. Their testimony got replaced by a medical who likely had a conflict of interest (even uf just working with the people who did that and want that outcome there’s v strong ‘organizational influence’ and culture issues etc)

I’m really puzzled about the Hoover sign - they are so fervent about extolling their ‘rule-in’ claims it is hard to work out if it’s belief (self convincing to the point they can’t question it) or even they don’t believe but they do know that claim being said assertively eith no room for checking or saying ‘it needs to be done by a qualified x,y,z’ . But it’s ok cos those assigned that group based on Hoover had Hoover when they checked, so ‘Hoover works to differentiate’ but who? - I’m not sure whether those people had been receiving the treatment before that or whether somehow that cures but not the Hoover thing.

Thing is, is anyone (who isn’t looking to label everyone FND) doing a Hoover census to see what % of normal population or CJD or Parkinson’s and so on have Hoover, with lots of anonymity to make sure no one looks them up and tries to suggest they have FND if it’s large proportion of those conditions that just have different diagnostics to hang their hat on .

It would be interesting to line up healthy/ non-FND medical academics as participants in a trial/test (on basis it’s people who if they decline the label they might be listened to) with (or without) a small number of FND labelled but whose lower legs wouldn’t be obviously different demographics to say bps neuro people as a sample that supposed Hoover testing experts have to play ‘find Wally’ blindly with by the participant being seen lying down and hidden from waist up and not speaking etc