functional neurological disorder

By David Tuller, DrPH

In a post last week, I noted that experts in FND have a tendency to assert prevalence rates that ignore their own diagnostic criteria. Before offering further thoughts on that score, I want to make one point very explicit: I am in no way questioning whether people with the diagnosis have serious disorders and very debilitating symptoms. Of course they do! And of course they deserve the best medical care available, like everyone does.

I have not suggested and do not believe that FND patients are hypochondriacs, hysterics, fakers or whiners. Perhaps that hasn’t been clear from previous posts. If anyone has interpreted my work that way or has criticized FND patients based on my posts, I really apologize for the misunderstanding. That has never been my intention. It has, of course, been my intention to raise concerns about how experts in the field have themselves generated confusion with contradictory statements about FND diagnoses and prevalence.

In talks and presentations, FND experts come across as sensitive and caring clinicians who clearly want the best for their patients. I have zero reason to doubt that. But whether doctors demonstrate compassion is a separate issue from whether it is acceptable to disseminate prevalence claims that go way beyond the established clinical criteria. Perhaps someone raised this problematic issue at the recent gathering, in Boston, of the Functional Neurological Disorder Society—but I doubt it.

It is true, as some have noted, that I haven’t included the voices of FND patients in my half dozen or so posts on this issue. While my focus is on questionable claims in the medical literature, I understand why this absence has bothered some patients. I’d like to rectify the omission by recommending an excellent, recently posted essay called “Cadenza for Fractured Consciousness: A Personal History of the World’s Most Misunderstood Illness.”

The author, a patient who goes by @FNDPortal, provides an overview of the history and development of the construct as well as a harrowing account of his own condition. Here’s an excerpt from the opening section:

“Late in 2013, I inexplicably lost my ability to walk. It happened over the course of just a few weeks; fast enough to be terrifying, slow enough to feel everything in crystalline detail…First, I could no longer manage my usual walk across town. Then I couldn’t reach the end of the parking lot. Then the other end of the house.”

Yikes! Terrifying indeed!  

If anyone believes FND patients are not struggling with something really awful, this essay will quickly alleviate them of their misconceptions. They will also learn a great deal about the FND patient perspective—or at least this particular FND patient’s perspective. He describes his search for answers, his appreciation of the FND diagnosis and related treatment approaches, and the improvements he has experienced over time. However, as enlightening as the essay is about many aspects of the issue, it does not resolve some of the questions I have raised since I first posted on FND in December, 2019.

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A “rule-in” diagnosis, or not?

My post last week examined how FND experts have presented inconsistent information about prevalence rates of the condition. Based on the requirement that FND is now a “rule-in” diagnosis relying on positive clinical findings and not a diagnosis of exclusion, these cases account for close to 6% of outpatient visits to neurology clinics—per an exhaustive study into attendance at Scottish neurology clinics. Here, as I noted in my previous post, is a 2016 statement on the numbers from FND experts Alan Carson and Alexander Lehn, from UK and Australia, respectively:

“The recent changes…to a definition based on positive identification of physical symptoms which are incongruent and inconsistent with neurologic disease and the lack of need for any psychopathology represent a significant step forward in clarifying the disorder. On this basis, FND account for approximately 6% of neurology outpatient contacts.”

Yet FND experts themselves routinely declare that prevalence in outpatient neurology clinics is 16%, or even a third. These numbers represent either a tripling or heptupling (is that a word?) of the rule-in rate. 

Here’s just one example, from Richard Grunewald, formerly the clinical director of neurosciences at Central Sheffield University Hospitals NHS Trust, in a recent blog for an organization called Inneg. (Inneg describes itself as “a leading agency specialising in providing Clinical Negligence, Serious Injury and Complex Case reports.” In other words, if you’re involved in litigation related to FND, better call these folks for help.) Grunewald’s post is called “The Challenge of Distinguishing Unusual Neurological Symptoms from. Malingering.”

Here’s what he writes:

“One common problem in neurological medicolegal practice is diagnosing Functional Neurological Disorder (FND), sometimes known as somatization, conversion disorder, hysteria or medically unexplained neurological symptoms…It is common, and has been estimated that it comprises about one third of the workload of most neurologists, yet is poorly understood.”

Is Grunewald aware that FND is now a rule-in diagnosis and not simply a placeholder term for anything unexplained by current neurological understanding? He seems not to know that the established prevalence via positive identification is “approximately 6%”–as Carson and Lehn reported. Whether Grunewald is familiar with these data or not, he and other experts in the field continue to fudge the diagnostic boundaries by citing prevalence rates of 16% or a third.

In a 2021 article, the authors described confusion among neurologists about how and when to code patients as having FND and noted that a major factor was “the outdated belief that FND is a diagnosis of exclusion.” (In other words, some or many neurologists do not understand that FND is now considered a diagnosis of inclusion, based on the rule-in signs.) The authors also stated that FND “accounts for 16% of consultations”—even thought that number combines both the “approximately 6%” identified by rule-in signs, per Carson and Lehn, plus another 10% who were assessed as having “psychological symptoms,” according to the data from Scottish neurology clinics.

Yet having “psychological symptoms” is not considered a clinical rule-in sign for FND, as is required for the diagnosis. So what is the authors’ rationale for combining these two smaller groups into one larger FND category? They provide no explanation. Perhaps they don’t recognize that they are contradicting themselves. The FND literature is full of examples of this sort of internal inconsistency and epidemiological incoherence.

People, this is not rocket science! (Or perhaps that should be: “People, this is not neuroscience!”) It is basic statistics, logic, and public health. After all, investigating disease prevalence rates is a core public health function. I have never pretended to have a medical education or an advanced degree in biology–much less neuroscience. But such training is not needed in order to notice that experts are citing multiple prevalence rates for the condition.

If FND is now a rule-in condition, I would argue that anyone without rule-in signs who has been given the label has been misdiagnosed. Much clinical guidance in recent years has focused on how to execute these rule-in strategies and why positive identification through such incongruities in clinical presentation is necessary to render the diagnosis accurately. Don’t take my word for it. Here is Jon Stone, a colleague of Alan Carson’s from the University of Edinburgh, in a 2021 presentation to the Encephalitis Society:

“Some people think that FND is a condition you diagnose when someone has neurological symptoms but you can’t find a brain disease to go along with it. And that’s absolutely not the case. Some people [i.e. clinicians] do that, but if they’re doing it like that they’re doing it wrong.”

From my interpretation of this authoritative statement, anyone claiming that the prevalence of FND is greater than the “approximately 6%” cited by Carson and Lehn is “doing it wrong.” Yet Stone and Carson themselves wrote in a 2020 paper that FND is the “second commonest reason for new neurology consultations”—a claim based on the 16% prevalence rate. In contrast, based on the “approximately 6%” prevalence, FND is much farther down the list of common neurological presentations.

This is all kind of weird. Why aren’t neurologists following their own FND criteria in their prevalence pronouncements?

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Rebranding and reframing FND

Here’s how this confusion might have developed over time. By all or most accounts, it seems that around a third of outpatient neurology attendees present with symptoms that do not conform to known patterns of neurological disease, as currently understood. The Scottish neurology clinic study, for example, reported that 30% of outpatient consultations–not quite a third–involved cases that could not not be explained by “organic disease.” Rather than identifying some or all such unexplained symptoms and conditions by old standbys like conversion disorder, hysteria or other terms often perceived as insulting, neurologists began decades ago promoting the need to call them “functional” instead.

Ok, rebranding a disorder with a less stigmatizing term is a step forward. And many patients report that they feel more respected, believed and cared for than when the condition was called something else. (Other patients report that, in their experience, doctors have changed their language but not their dismissive attitudes toward the illness.)

Along with the new name, neurologists pushed for a revision of the diagnostic criteria. They recognized that not every patient in this cohort had identifiable psychological distress or trauma that could, in their view, account for the symptoms—a requirement under the longstanding definition of conversion disorder. That requirement was therefore removed in the description of the illness enshrined in the fifth iteration of the so-called psychiatric bible known as the Diagnostic and Statistical Manual (DSM).

The experts further posited that certain clinical tests provide affirmative evidence of the “functional” rather than “organic” nature of the symptoms—Hoover’s sign being the most prominent. (The essay from @FNDPortal provides a helpful discussion of these strategies.) So the updated description in DSM-5 also noted that evidence from such rule-in signs is necessary for rendering an accurate diagnosis.

It would be a significant improvement if patients with symptoms not consistent with standard neurological understanding but without the mandated rule-in signs were said to have idiopathic neurological disorders or neurological disorders of unknown etiology. But perhaps because the field has become so used to regarding all unexplained symptoms as “functional” rather than “organic,” experts still seem to use the FND label when writing or talking about this larger group of patients without rule-in signs.

So who cares? Don’t all these patients need medical care and treatment, whether their illness is called FND or neurological disorder of unknown etiology?

Of course they do. But clinicians conduct medical investigations so that they can render a diagnosis. Once they have rendered the diagnosis, they move on to providing care and treatment based on that assessment. The literature on “medically unexplained symptoms,” a larger category of which FND is a major subset, is replete with warnings that once the diagnosis has been established, continuing to investigate possible medical causes of somatic complaints serves to feed patients’ purportedly unjustified fears that they have underlying but undiscovered pathophysiological dysfunctions.

I don’t know exactly how this dynamic is playing out in clinical care. But it is indisputable that those referencing prevalence rates of 16% and a third, whether in the medical literature or in public presentations, are not adhering to the rule-in rule they have themselves promoted. In medicine, as in public health, consistency in communication and messaging on core issues like disease prevalence is essential. The FND field so far has fared poorly on this front.

FND is either a diagnosis of inclusion, or it isn’t. Citing prevalence rates far higher than the “approximately 6%” identified by rule-in signs risks turning FND into another wastebasket diagnosis of exclusion—a dumping ground for any symptoms as yet unexplained.