Review Systematic review of movement disorders mislabeled as functional: when incongruence misleads 2026 Marín-Medina et al

[Andy]

Abstract​

Background​

Misdiagnosis of functional movement disorders (FMD) remains a concern for clinicians. We sought to review the phenomenology and clinical features associated with FMD misdiagnosis.

Methods​

We conducted a systematic review of case reports, case series, and observational studies of adults diagnosed with FMD and subsequently reclassified as having another neurological or medical condition. PubMed was searched from inception to September 13, 2025, focusing on reported features of inconsistency, incongruence with known diseases, and low-validity features. Isolated (iMD) and mixed (mMD) movement disorders were analyzed separately.

Results​

Forty-two included studies comprised 150 patients, of which 73 cases underwent detailed analysis. Gait disturbance (35%) and dystonia (27.5%) were the most common iMD phenomenologies (n = 40), while jerks and rigidity (24%) were the most common mMD phenomenology (n = 33). Incongruence with known diseases (50.7%), psychological factors (34.2%), and symptom variability (31.5%) were the main factors associated with misdiagnosis. Application of incongruence alone was associated with the highest rate of FMD misdiagnosis, similar to that of applying neither incongruence nor inconsistency (49% in both cases). Conversely, reliance on inconsistency alone was least associated with an FMD misdiagnosis (13.7%). Misdiagnoses of iMD were more likely in the absence of documented inconsistency (OR 3.94, 95% CI 1.32—12.82).

Conclusions​

FMD misdiagnoses, particularly of gait disorders and dystonia, were most commonly associated with the application of incongruence as diagnostic criterion. The lowest rate of FMD misdiagnosis was associated with ascertaining at least two positive neurological signs of inconsistency.

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[rvallee]

FMD misdiagnoses, particularly of gait disorders and dystonia, were most commonly associated with the application of incongruence as diagnostic criterion

So, misdiagnosis is associated with the main, iffy criterion of a problematic diagnosis. Sounds like a problem. Not that this should surprise anyone, but it will likely bother no one involved with the concept, unfortunately.

 

[cstruter]

It aligns with what I’ve discussed on FND Nope. The FND label can become a premature endpoint, resolving uncertainty too early and risking missed or evolving organic pathology.

A simpler explanation often exists. Within a Bayesian brain / predictive processing model, learned patterns after real injury can persist as faulty predictions, effectively acting like programmatic scar tissue in the CNS. This can produce variable, “incongruent” gait without being labelled FND.

The takeaway is simple. Incongruence alone is weak evidence. Prior injury should lower suspicion of FMD. Only multiple clear inconsistency signs should shift diagnosis in that direction.

 

[Jonathan Edwards]

A simpler explanation often exists. Within a Bayesian brain / predictive processing model, learned patterns after real injury can persist as faulty predictions, effectively acting like programmatic scar tissue in the CNS. This can produce variable, “incongruent” gait without being labelled FND.

But simple explanations without any supporting evidence are of no clinical value. And, as we have discussed at length on this forum, the predictive processing model invoked by people like Mark Edwards actually makes the wrong prediction about clinical outcome, so is worse than useless.

Best to keep away from pseudoscience like this masquerading as real physiology.

 

[cstruter]

I think my point is similar. If predictive processing is used to explain a functional presentation, its value may remain largely theoretical rather than directly clinically actionable. It is like observing a scar without knowing what caused it or whether the same mechanism is still active. That may be academically interesting, but its clinical utility is limited if the underlying mechanisms cannot be specified at the individual level.

 

[Utsikt]

I think my point is similar. If predictive processing is used to explain a functional presentation, its value may remain largely theoretical rather than directly clinically actionable. It is like observing a scar without knowing what caused it or whether the same mechanism is still active. That may be academically interesting, but its clinical utility is limited if the underlying mechanisms cannot be specified at the individual level.

There is no use for theoretical models that are not grounded in reality.

Predictive processing makes no sense for symptoms because there is no need for high accuracy.

It make sense for coordination because the nerve signals from hands are too slow to achieve high enough accuracy to interact with fast objects and movements in 3D space. So we can fool it.

Search for «noakes» on the forum, restricted to posts by the user Snow Leopard to find most of the discussions and studies falsifying the hypothesis of predictive processing causing symptoms.

 

[Jonathan Edwards]

If predictive processing is used to explain a functional presentation, its value may remain largely theoretical rather than directly clinically actionable.

My point is that it gives the wrong answer so is worse than useless - incoherent.
It also falls into the usual trap of assuming that you can explain disease using normal regulatory models. By definition normal regulatory models predict normality not disease. A disease model has to involve an explanation why the model of normality, whether predictive processing or Pavlovian reflex, does not apply. Without that you have the sort of buzzword salad theorising that Freud made so popular - the paradigm of what is not science.

 

[Theresa]

I think for FND they say something like the topdown signalling due to prior expectations is overriding the bottomup normal signalling whereas for diseases the bottom up signalling is correctly interpretred,

 

[Jonathan Edwards]

I think for FND they say something like the topdown signalling due to prior expectations is overriding the bottomup normal signalling

Yes but if it did you should feel unusually well! If the expectation is bad and the input isn't then you should feel extra good on a predictive coding model.

 

[Theresa]

A very good point. Does it follow from this that there's nothing in the brain that can cause the person to be unable to experience the bottomup input accurately irrespective of their expectations i.e. no disorder of topdown voluntary processes where for example somebody thinks they can't move their arm when they are focussed on it but apparently can move it when distracted ? I have always been sceptical of this. It seems the whole FND thing doesn't make any sense.

 

[Utsikt]

And people don’t feel pain during the rubber arm experiment, even though they are convinced for a brief moment they got stabbed.

When you lift something and it was a lot lighter than you thought, you don’t feel fatigue, get a fever or feel pain. You feel strong, or just surprised.

When you try natural blood doping from high altitude mountaineering, you feel amazing on the way down and can run for what feels like forever.

 

[Sean]

It seems the whole FND thing doesn't make any sense.

That would be because it doesn't contain any.

It just doesn't add up. It really is that simple.

Yet it thrives. At our expense.

 

[Liie]

Studies like this is great for advocacy as counter-argument to the functionalist crowd.

 

[rvallee]

The takeaway is simple. Incongruence alone is weak evidence. Prior injury should lower suspicion of FMD. Only multiple clear inconsistency signs should shift diagnosis in that direction.

Oddly enough, I think I've mostly seen the opposite, because it "better" matches their model where there might be a precipitating event, but the functional part is psychobehavioral. In fact, it might be the next frontier, it would be easy to waste decades on this, as with it comes the 'acknowledgement' that the initial trigger was 'real', but the functional part remains. Then they can continue to clown around with permutations of 'expectations' and 'predictive coding' and all this irrelevant junk.

Heads they win. Tails they win. Don't toss they win. No coin they win. They just win. What a system.

 

[Yann04]

The lowest rate of FMD misdiagnosis was associated with ascertaining at least two positive neurological signs of inconsistency.

„Inconsistency“ still risks catching ME/CFS.

Modified version of a comment I made in another thread:

I’ll take my example of when a neurologist suggested my illness was explained by Functional Neurological Disorder. I told them I can barely walk. I don’t mean I can’t walk in a straight line moving my arms. I can. If the neurologist sees that, they’ll see me walk fine and then assume there’s a discrepancy between what I believe I can do and what I can do.

But this discrepancy is simply explained by PEM the main feature of ME/CFS. Yes I could ride my bike (well not anymore i‘d faint but like back then I could), but it would decline my health permanently.

I did do the hoover’s sign assessment. And the neurologist said I tested positive for inconsistencies. To him it looked like I could walk. What he didn’t see is that assessment made my health decline and it’s been 2.5 years and it’s still not better. I now can’t even sit up.

So when people with ME/CFS say “I can’t do [X]”. They mean “I can’t do [X] without risking my health and getting horrible consequences.”

And as long as medics don’t try to understand that. We will constantly test positive for „inconsistencies“ like Hoover‘s sign.

 

[Peter T]

Inconsistency will inappropriately catch so many biomedical conditions. For example relation to many conditions triggered by demonstrable neurological damage an individual may vary in performance of complex cognitive tasks from minute to minute or hour to hour.

When I was researching acquired reading and spelling disorders (primarily in stroke patients) often I did not see exact cut offs rather a balance of probability. It hardly makes sense to hypothesise a functional disorder to say why an individual could generally not read or spell specific classes of words but could read or spell others. I remember one incident with someone who struggled to read aloud irregularly spelt words: they stared blankly at the letters g-a-u-g-e for several minutes, then as an aside said ‘I can never read /gauge/‘ and then went back to staring at the letters failing to read the word aloud.

Alternatively why would you seek a functional explanation as to why someone could write words they knew, but not represent simple sound sequences as letters, when we know they have damage to the language areas of the brain, It might seem as inconsistent that someone could write to dictation ‘antidisestablishmentarianism’ quite easily but be totally unable to attempt a written representation of the nonsense word ‘fip’.