Functional Neurological Disorder (FND) is a clinically heterogeneous disease which manifests as neurological-ish symptoms that are not due to structural change or aberration in the nervous system. (Except that there are actual differences in structure.)

BMJ just published a new review on FND. It’s actually kind of a banger even if it doesn’t cite my favorite recent theoretical paper on the subject. Among other things it includes several rather large and inclusive tables of validated signs in FND subtypes. A younger me—still in residency, anxious, terrified, miserable—wrote an unpublished manuscript talking about the various physical exam maneuvers that could be used to detect functional etiology. I was a naïve spike-wave back then, with an incipient neurologist’s overworked disdain for “non-organic patients”; in many ways the manuscript was about collecting my thoughts so I could be more efficient in disposing of consults with functional etiologies. It was also about my neurodivergent squee about systematizing, collecting, and categorizing. In any case, this paper is not only more scholarly and more complete, but it’s available to read to boot.

Figure 1 is a cartoon summarizing some of the neuroanatomic and pathophysiologic aspects that have been elucidated along with half an article’s worth of caption below it.

I find Jungilligens et alii’s recent paper “A new science of emotion: implications for functional neurological disorder” to be the most interesting of the 2020s work on etiology. It builds on well-established work on the constructive theory of emotion that is nevertheless poorly understood outside of the field, as attested by the presence of coauthor Lisa Feldman Barrett. Among their theses is that interoceptive information which is normally accounted for by an emotion can instead be interpreted as a primary and physiologic problem. It is admittedly a dense read for an epileptologist or neurophysiologist unused to thinking about emotion category construction or the role of the brain in preserving allostasis. But, for me, it does the hard work of linking neurologic and psychological pathology in a novel way.

The BMJ review probably makes a little too much hay of the terminological issue (the Functional Neurological Disorders Society is up and running and not about to change their name). The section on nosology is a little dry but probably still helpful. What’s most enraging—and not at all the fault of the authors—is that the section on treatment is not so helpful.

This is the state of the art (and BMJ brands this paper a “state of the art review”) in 2023: we have come to understand FND much better than ever before; to start to eliminate stigma; to understand the scope of the problem; to theorize rigorously about its pathophysiology; and to recognize that it is not a diagnosis of exclusion and it is not merely the expression of psychological distress. But we still don’t know how to really help those who suffer from it.

Despite all the advances in understanding real physical and physiological differences in FND sufferer’s brain—a brewing understanding of the truly organic nature of a supposedly non-organic disease—we still tell people to go to therapy and hope for the best. As long as they don’t live in a place where therapy would be hard to get. Or have comorbidities or socioeconomic difficulties that make therapy difficult to adhere to. Which means the real message we use to undercut our savvy talk about the complex pathophysiology of FND is “it’s not in your head but you need to do therapy as if it were in your head and by the way good luck finding it.”