Functional neurological disorder, or FND, is the new-ish name for the hoary Freudian construct known as conversion disorder. For decades, psychiatrists informed patients that they were “converting” their emotional distress and anxieties into physical symptoms like tremors, seizures, sensory and cognitive deficits, a halting gait, or other physical dysfunctions. The impossibility of proving such claims did not seem to impact psychiatry’s acceptance of the concept or the certainty with which it was applied to patients with unexplained conditions.
Other terms that have been used to describe such symptoms are psychosomatic or psychogenic disorders, hysteria, and the like. These descriptions, which highlight the belief that the conditions are driven by psychological disturbances, have often been regarded as condescending and dismissive. More recently, however, the more neutral-sounding term “functional” has been increasingly adopted to make the diagnosis more palatable to patients, among other reasons. That makes some sense. After all, these syndromes feature deficits in function that resemble standard neurological complaints. And some or many patients who receive a diagnosis of FND, often after years of feeling belittled, overlooked or abandoned by the medical profession, might experience significant relief just from being given an actual name for what they are experiencing. I get that.
I have previously written posts questioning the term FND because it has seemed to be a so-called “wastebasket” diagnosis–just like conversion disorder. Whatever could not clearly be identified as a dysfunction explained by current pathophysiological understanding seemed at risk of being called FND, as it had previously been labeled conversion disorder.
Yet the FND experts have addressed this issue. The change in name has been accompanied as well by changes in the description of the condition in the latest version of the so-called “psychiatric bible,” the Diagnostic and Statistical Manual.
Although conversion disorder remains the heading of the category, the DSM-5, published in 2013, now includes “functional neurological symptom disorder” as a synonym. (Note: After posting this earlier, I found out that the DSM-5 last month swapped out the names, with functional neurological symptom disorder becoming the main heading and conversion disorder offered as a synonym.) According to the new criteria, identification of psychological distress, once considered to be a necessary component of conversion disorder, is no longer a requirement for diagnosis—although proponents say it can still be a factor in the genesis of the condition. (In
a 2020 presentation on FND, for example, Mark Hallett from the US National Institutes of Health noted in one slide that the condition is “sometimes due in part to a psychological cause.”)
Moreover, FND experts have been advocating the notion that the condition is now a “rule-in” diagnosis based on “positive” signs—not just a dumping ground for all symptoms that don’t fit standard or recognizable neurological or pathophysiological patterns. This need for confirmatory evidence has also been incorporated into the DSM-5 description. The requirement has implications for calculating prevalence rates for FND.
In 2016, Alan Carson and Alexander Lehn, two leading FND experts from the UK and Australia, respectively, made this point explicit in
the abstract of a chapter on the epidemiology of the condition:
“The recent changes in DSM-5 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.”
