By David Tuller, DrPH
When I have previously written about functional neurological disorder, or FND, I have gotten flack from FND patients. I understand from these exchanges that some have taken what I have written as criticizing patients with these diagnoses or dismissing their suffering. That is certainly not my intention. I know these conditions can be extremely disabling. I have recommended this comprehensive piece written by an FND patient, who provides a compelling account of his own illness as well as a history of recent developments in the field.
My concern in this area has always been with claims made by experts that are not supported by the research they conduct or cite. FND experts routinely emphasize that the diagnosis is not a so-called “wastebasket diagnosis”—that is, a diagnosis of exclusion given only after ruling out other possibilities. Instead, they note, it is a diagnosis that should be rendered only if a patient exhibits recognized “rule-in” signs during a clinical examination.
In the current (fifth) edition of the Diagnostic and Statistical Manual (DSM), “functional neurological symptom disorder” is provided as a synonym for the old Freudian construct of “conversion disorder.” Whereas earlier definitions of the condition required the presence of psychological trauma, the updated definition does not. And the DSM-5 does now require the presence of positive clinical signs to diagnose FND.
But that’s not how things necessarily seem to operate in practice. Let’s take a recent example: a paper in the journal Brain positing that postural orthostatic tachycardia syndrome (POTS), a dysfunction of the autonomic nervous system, is a “psychogenic disorder.” (I first wrote about this paper, called “Fear conditioning as a pathogenic mechanism in the postural tachycardia syndrome,” here.) I have heard from patients of having been told by a neurologist that they had FND, and then subsequently being diagnosed with and treated for POTS by another clinician. So it matters if physicians think patients who report dizziness and nausea upon standing have FND and are experiencing a conditioned but unwarranted fear of being upright, or if they might in fact have POTS.
The paper in Brain, from the neurology department at NYU Langone Health, is a paragon of misinterpretation and is likely to amplify such diagnostic confusion. The investigators have clearly conflated association with causation. It is perplexing that they have overlooked the most likely explanation for their data.
This is the gist of their argument: Compared to patients without POTS, patients with POTS exhibit an increased heart rate when told they will soon undergo a tilt table test. Per the theory, the POTS patients likely had an earlier episode of feeling dizzy upon standing, which so imprinted itself on their consciousness that they now experience an increased heart rate just upon anticipation of standing. Therefore, the increased heart rate that characterizes POTS is generated by fear and anxiety associated with standing up, and not by being upright itself.
Yup. That’s the argument. When I first read the paper, I didn’t get it. The logic seemed upside down. I had to review it more than once to fully grasp that this was actually what they meant. They ignored the glaringly obvious point that it is completely understandable that patients with POTS would experience anxiety over an imminent tilt table test, since they know the test will cause unpleasant symptoms. The evidence does not support the tortured putative mechanism promulgated by the NYU investigators.
Brain has just published the letter I sent about the paper, which was co-signed by eight other academics and physicians, along with additional correspondence questioning the paper’s reasoning. (Unfortunately, the letters are behind a paywall. You can read the letter I sent here.) I hope the NYU team will respond to the questions raised by us and other puzzled readers, although in my experience this sort of authorial rebuttal can involve repetition of points already debunked by the letter-writers.
One interesting point is that the NYU team chose the word “psychogenic” to describe what they believe is occurring—even as some FND experts seek to move away from that term, preferring to explain the possible mechanisms involved in more complex and less reductive ways. That’s why, for example, there has been an effort to rechristen psychogenic non-epileptic seizures (PNES), a term widely used in the medical literature, as “dissociative seizures”—a name perceived as less dismissive and insulting.
Patients tend to dislike being told their physical symptoms are psychogenic—or psychosomatic, a related but more frequently used word–so I wonder what the NYU Langone investigators were thinking. Given that such articles continue to be published, it is easy to understand why there remains some confusion about whether any change in approach is largely semantic and whether FND, in the minds of many neurologists, is still just a kinder, gentler name for psychogenic or conversion disorder.
(Originally posted on Virology Blog.)