Trial By Error: Unconvincing Response to Letter on FND Prevalence Inflation

By David Tuller, DrPH

As I wrote in a post the other day, the journal NeuroImage: Clinical has just published a letter from a group I organized about the misrepresentation of findings regarding the prevalence of functional neurological disorder (FND). They have also published a response from the authors of the article we criticized. The findings in question were from the Scottish Neurological Symptoms Study (SNSS), a major project that yielded multiple papers a dozen or so years ago.

Since then, more than 50 peer-reviewed articles have asserted, citing the SNSS, that FND prevalence at outpatient neurology clinics is 16% and/or that FND is the second-most-common diagnosis in those venues. In fact, as our letter explained, the only acceptable rate for FND to cite from the SNSS is 5.5%, which represented the patients diagnosed with conversion disorder symptoms–gait and motor disorders, non-epileptic seizures, and sensory deficits–and categorized in the study as “functional.” (Conversion disorder is the former name for FND.) The higher rate was for a group that included many participants who were labeled collectively as having “psychological” diagnoses, yielding a much larger combined “functional/psychological” category.

When we initially wrote to NeuroImage: Clinical about the inflated prevalence claim in one of those 50+ articles, a 2021 paper called “Neuroimaging in functional neurological disorder: state of the field and research agenda,” the journal and the authors quickly agreed to a correction. Our group felt that the proposed correction, as written, was an inadequate remedy. But we accepted it as the best that could be achieved.

After the correction had been agreed upon, I sent a letter to the lead and senior authors of the NeuroImage: Clinical paper. In the letter, I thanked them for agreeing to correct the citation and then urged them to correct the related misrepresentations of the SNSS in several other papers for which one or the other was either the lead or senior author. (This number did not cover the many other papers in which one or both served as a co-author but not the lead or senior author.)

I didn’t hear back. Not long after, however, the journal informed me that the authors had withdrawn their agreement to a correction. What?? I found this hard to understand. What kind of investigators would withdraw their agreement to a correction? Were they surprised or pissed that I would urge them to correct their other papers? Wouldn’t they have realized or assumed that a correction in one paper would require a correction in other papers with the same error?

The other co-signatories of the letter were as flabbergasted as I was. None of us had previously heard of anyone withdrawing an agreement to issue a correction. Presumably the authors found the prospect of contacting many other journals about the need to correct false assertions too unappealing to contemplate.

Instead, the journal invited us to submit a letter as correspondence. Under the circumstances, we agreed. The letter went through two rounds of peer-review; both our initial and later versions were also posted on a pre-print server. (They can be read here and here. It is easy to discern some of the changes that occurred during this process. For example, our initial letter highlighted the authors’ agreement to correct the paper, and their subsequent withdrawal of this agreement; the final version did not.)

Complications continued even after acceptance. For some reason, the journal ended up publishing the authors’ response to our letter before publishing the letter itself. That has been rectified, and both our letter and the response are now online.

Our point is pretty simple. FND is not synonymous with the SNSS’s category of “functional/psychological” and should not be presented as if it were. As our letter noted, what happened here is an example of the phenomenon known as diagnostic creep. The authors made a bold assertion, and then cited a study that very clearly did not support it. It is self-evident, or should be, that misrepresenting the findings from a study being cited is unacceptable.

Not surprisingly, the paper’s authors don’t agree with us. But these are among the leaders in the field of FND, so they have a lot at stake in debates about prevalence—as is clear from the very extensive list of “declared conflicts of interest” appended to the article itself and their response to our letter. (Of course, I have my own “declared conflicts of interest” related to my crowdfunding support.)

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Trying to prove FND is the same as “functional/psychological”

In the authors’ response, they acknowledge what is indisputable—the claim that FND is the second-most-common diagnosis was based on a reinterpretation of the data from the study being cited. They then offer four paragraphs of rationalizations and justifications for why, in their view, it was legitimate to equate FND with the “functional/psychological” group in the SNSS. Let’s review.

Paragraph #1: The sentence was a “scene setting statement” meant to make a “brief comment,” and the epidemiology of FND wasn’t “the focus of our paper.”  

It is hard to see the relevance of these points.  That the intent was to make general comments about an issue that was not the focus of a paper is not an acceptable rationale for violating appropriate reporting and citation practices. A statement should never flagrantly misrepresent the reference being cited in support, whatever the context. Furthermore, the scene-setting nature of the sentence is part of what makes the citation so offensive and ethically untenable, since the authors are presenting their distortion of the data in the article’s opening paragraph as a blanket assertion of fact.

Paragraph #2: The “functional/psychological” category in the SNSS is pretty much equivalent to what we would call FND now. 

This long paragraph is the heart of the authors’ response, and it is one big fudge. Here is the core of the defense, in which the authors explain who fell into the “functional/psychological” group besides those with conversion disorder symptoms:

“Others were labelled as…“non-organic” and others received a psychiatric diagnosis like anxiety and depression, but would have had neurological symptoms in order to be referred to a neurology clinic. Some other patients had problems like dizziness and cognitive difficulties likely equivalent to modern diagnoses of functional dizziness and functional cognitive disorder that are now considered part of FND.”

This explanation makes our point for us. Having unexplained symptoms labeled “non-organic,” or having anxiety or depression plus neurological symptoms, does not equate to an FND diagnosis; neither does being dizzy or having cognitive difficulties. Just because some people with those complaints might now be diagnosed as having FND by exuberant proponents of FND does not excuse the wholesale reinterpretation of the diagnoses actually received by all the anxious, depressed, dizzy and cognitively impaired participants in the SNSS.

Then, the authors state this: “So, the category refers to a broader grouping of functional neurological symptoms that clinical neurologists will recognize.” Again, this statement confirms our criticism. In the sentence we questioned from the 2021 paper, the authors authoritatively declared that FND was the second-most-common diagnosis. Here, they appear to concede that they were using FND as a short-hand for this “broader grouping”—whether or not those in this “broader grouping” meet the required FND criteria. In other words, the same experts who insist that FND is not a diagnosis of exclusion but requires rule-in clinical signs are willing to overlook that requirement and identify a “broader grouping” when they want to claim higher FND prevalence rates. They apply one set of criteria when discussing diagnosis, and a much looser one when discussing prevalence.

Paragraph #3. Subsequent papers have endorsed the higher rates.

Like paragraph #1, this point is irrelevant to our concerns about the authors’ decision to misrepresent the findings from a seminal paper in the field. They didn’t cite other studies; they cited a specific study. Furthermore, the SNSS remains the most extensive study of its kind, including many more participants and involving many more neurologists than either of the other two studies mentioned by the authors.

4. Where diagnoses rank in these kinds of lists depends on lots of factors.

Like paragraphs #1 and #3, this point is irrelevant. The concern expressed in our letter did not involve general issues about the complexities of ranking a list of diagnoses. Whatever those complexities are, they do not justify misrepresenting findings from a major study. The authors themselves chose to rank FND as the second-most common diagnosis at outpatient neurology clinics. Now they want to lecture and opine about the various factors that impact rankings.

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The bottom line here is this: A group of distinguished researchers misrepresented key data from a prominent study in their field. They got called out. Instead of forthrightly acknowledging their mistake and correcting it, they have issued an unconvincing response—in the process documenting the validity of the criticism.

4 thoughts on “Trial By Error: Unconvincing Response to Letter on FND Prevalence Inflation”

  1. I feel this response to your pointing out the authors’ obvious miss citation indicates that they are not interested in scientific accuracy or logical consistency, but rather pushing a belief system. It is logically possible that FND is now the second most common condition seen in neurology clinics but the authors do not objectively evidence that claim, but it is also possible that FND as a diagnosis reflects the preconceptions of some researchers and clinicians and that it does not have a meaningful clinical reality (which is not to say that people so diagnosed do not have very real but potentially very misunderstood neurological issues).

  2. Is there need for anyone to comment further? To my mind, David’s response here completely invalidates the response by the authors to the letter, and he puts it all so clearly. Frankly, I don’t know how they had the brass nerve to offer up what they did.

    But there are a few points I’d like to add:

    First, thanks David for setting the record straight on what the history was that led to the publishing of the letter. It think it’s bizarre that a correction would be agreed and then retracted.
    David wrote: “The other co-signatories of the letter were as flabbergasted as I was. None of us had previously heard of anyone withdrawing an agreement to issue a correction. Presumably the authors found the prospect of contacting many other journals about the need to correct false assertions too unappealing to contemplate.”
    That’s reminded me of that Tolchin et al (2021) paper -https://www.sciencedirect.com/science/article/pii/S258998642100068X?via%3Dihub that David blogged about before with its 16% prevalence claim -https://virology.ws/2023/02/11/trial-by-error-once-more-regarding-inflated-fnd-rates-and-a-reprise-of-a-letter-to-a-yale-neurologist/ . Has there been any movement on that with regards to a correction? It looks like one of the co-authors of that paper is now the Editor-in-Chief.

    David wrote: ” The letter went through two rounds of peer-review; both our initial and later versions were also posted on a pre-print server, here and here. (It is easy to discern some of the changes that occurred during this process. ….)”
    What happened to the middle sentence of the 4th paragraph of the original letter (original letter copied here -https://virology.ws/2023/09/07/trial-by-error-letter-to-journal-about-diagnostic-creep-and-inflated-claims-of-fnd-prevalence/)? Why is that not in the final letter? It looked wholly accurate to me and was very measured in its tone.

    David wrote: “Complications continued even after acceptance. For some reason, the journal ended up publishing the authors’ response to our letter before publishing the letter itself. That has been rectified, …”
    But why is the authors’ response described/categorized/listed as a “research article” when it’s simply a response to the letter? Shouldn’t it be categorized as “correspondence”/”discussion” too? As far as I can see, it offers up no new research or insights into the research. Does anyone else find that rather pathetic?

    David wrote: ‘extensive list of “declared conflicts of interest” ‘.
    I’ll come on to that.

    David wrote about the authors’ first point in their response : ‘Paragraph #1: The sentence was a “scene setting statement” meant to make a “brief comment,” and the epidemiology of FND wasn’t “the focus of our paper.” ‘
    and delivered an obvious but very clear take down of their response. I would only add that I surmise from the authors’ response that they regard accuracy as not all that important or not a priority when it comes to the scene-setting of what they write in journal papers. However, in their conflicts of interest statement, a good number of them disclose that they do work in a legal context, for example, as expert witnesses. I’m left wondering then, what standards do they apply when scene-setting in that work and do they differ from their standards when writing journal papers? To my mind, standards in medical journalism should be no different to those demanded in legal work, because health and lives are at stake. It’s clear that the “second most common” FND prevalence claim has somehow found its way into the legal context e.g -https://www.stewartslaw.com/news/stewarts-expert-witness-training-webinar-2021/ and -https://www.stewartslaw.com/wp-content/uploads/2021/06/Dr-Parashar-Ramanuj-Decoding-FND_SN.pdf and it looks to me like the information supplied in the chart on page 3 of 15 in the latter is based on the Stone et al 2010 paper. NB I’m definitely not saying or implying that there was any intention to deceive with regard to that information. Doctors have to be able to take what they read in medical journals on trust, so there is no room for sloppiness on anything, whether it’s “scene-setting” or anything else. Everything researchers report must be backed up by evidence and by the references supplied. If medical journal authors/doctors and medical journal editors don’t understand that then I’d say they are in the wrong job.

  3. The purveyors of ‘FND’ seem to have tied themselves up like kippers, don’t they? This work, all the various blogs which David has written which underscore these egregious missteps in accuracy wrt claims about FND prevalence in neurology clinics, are unanswerable. And this sleight of hand, being played by the FND purveyors, is all ‘here’, clearly described in great detail in the *public domain*. The Post Office scandal was far more occult in its dealings… how on earth are these people, the FND purveyors, getting away with this? It’s scandalous.
    From where I’m examining this on the ‘outside’ it looks like a machine in action, lots of people of like-mind happy to ignore fact and embrace error, lots of people interconnected & happy to be a cog in this weird machine of FND orthodoxy collectively pushing back against David et al for the temerity to suggest their papers are flawed, their ability to cite accurately is missing and their widely advertised ranking/ prevalence of FND is wholly WRONG!. A machine which is, presumably, ‘useful, dangerous and habit forming’ for those who subscribe to whatever they think FND is, on whatever day, in whatever way, the machine has decided FND ought to be. Worrying.

    Replying to Peter Trewhitt: you said “..but it is also possible that FND as a diagnosis reflects the preconceptions of some researchers and clinicians and that it does not have a meaningful clinical reality (which is not to say that people so diagnosed do not have very real but potentially very misunderstood neurological issues).” From everything I’ve read about the construct, that would be my likely interpretation.

  4. To continue from my last comment, here are some questions to ponder:

    Is it just “scene-setting” if UK MPs are informed that FND comes second with regard to neurology outpatient referrals with seemingly no concrete evidence to back that up -https://www.fndhope.org.uk/we-need-your-help-in-writing-to-your-mp-to-request-attendance-to-our-inaugural-fnd-parliamentary-awareness-day/ ?

    Is it ok if the same prevaelnce information is provided in petitions to the UK and Canadian governments/parliaments that argue for extra research and service funding (respectively) -https://petition.parliament.uk/archived/petitions/194850 and -https://www.change.org/p/ask-the-canadian-government-to-increase-funding-for-fnd-functional-neurological-disorder ?

    Can we be relaxed about charities disseminating similar FND prevalence information to the general public, e.g. -https://www.thebraincharity.org.uk/what-is-functional-neurological-disorder/? NB 16% is given here rather than ‘second most common’ . …

    or about the UK public being informed via national news broadcasts that FND is the second most common reason for neurology consults -https://news.sky.com/video/campaigners-raise-awareness-of-fnd-12802930 (at 1.19 mins) and https://www.youtube.com/watch?v=8EMspXvKWd8 (at 4.25 mins)? NB I’ve no issue with the FND patient who I assume took the information to be well-evidenced.

    Does it matter if this 2023 paper -https://jnnp.bmj.com/content/94/10/855 indicates that FND comes second for prevalence in neurology clinics (citing Stone et al 2010) but one of its joint first authors plus its correspondence author co-authored another paper (along with other co-authors) published in the same year -https://onlinelibrary.wiley.com/doi/10.1111/ene.15892 that gives the prevalence of FND in the discussion section as just 5.4%, referencing a different Stone et al paper based on the same SNSS? And if the editor of the journal that published the aforementioned paper won’t correct the claim or even discuss these concerns with the person raising them, is that really of any consequence?

    Simple “scene-setting”? I don’t think so. On top of all of all this, I understand that the reasons given by an editor for not correcting a second most common claim were that it had been widely published/cited and was now generally accepted. Can we therefore assume that by relaying the same information over and over in paper after paper, doctors/researchers, editors or whoever can claim it to be fact now even if it’s garbage? Is this really what passes for science these days?

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