Functional Neurologic Disorder Series - Part 3

In part three of this seven-part series on FND, Dr. Jon Stone and Dr. Gabriela Gilmour discuss causes of functional neurologic disorder. 

Show citation: 

Hallett M, Aybek S, Dworetzky BA, McWhirter L, Staab JP, Stone J. Functional neurological disorder: new subtypes and shared mechanisms. Lancet Neurol. 2022;21(6):537-550. doi:10.1016/S1474-4422(21)00422-1

Show transcript: 

Dr. Gabriela Gilmour: This is Gabriela Gilmour with the Neurology Minute. Jon Stone and I are back to continue with part three of our seven-part series on functional neurological disorder. Today, we will focus on the causes of FND.

So Jon, there have been many advances in our understanding of the mechanism of FND in the last 10, 15 years. And so what do we know about this now?

Dr. Jon Stone: I think the key message I want to get across here is that whereas previously we had a very psychiatric, purely psychiatric view of FND, it used to be called conversion disorder, what we've got now is a multi-perspective view of the mechanisms, which mean that we can understand FND at a kind of neural level or brain circuit level, but we can also still retain the importance of psychological factors, traumatic events. And I think it's also important to separate out, as you've done here with a question, what's the mechanism? How is the symptom happening versus why is it happening? Which often people don't do.

So for this question, how is it happening? How is it that somebody, for example, gets a weak leg? Well, at a very simple level, their brain is disconnecting from their leg and that's what dissociation is. And you can explain that to patients at sort of brain circuit level. We've learned that there are disruptions probably in the circuits in our brain that relate to that sense of agency, the parts of our brain that tell us that our bodies belong to us. And people are particularly interested in an area called the temporary parietal junction.

And at a higher broader level, people are particularly interested in the idea that FND is a disorder that you would expect to happen based on our understanding of the brain as a predictive organ. So if the brain spends its time predicting things, maybe in FND what's gone wrong is this is very strong prediction that the leg is weak or that there's a tremor or that a seizure's about to happen that overrides sensory input telling our brain otherwise.

Dr. Gabriela Gilmour: And I guess to follow into that, you mentioned what is going on. So now can you talk a little bit about why somebody might develop FND or the etiology of FND?

Dr. Jon Stone:  I think this helps clinically as well as neurologists, because we can talk about mechanism as we would, for example, with MS as inflammation, but why is there inflammation? So okay, the brain's gone wrong, but why has it gone wrong? And there we need a much more complex view of multiple range of risk factors, predisposing, precipitating, and perpetuating that we know are associated with FND, but vary a lot from person to person. So no one person's the same.

If you've had traumatic experiences in the past, that will make you more prone to dissociation. If you've had other functional disorders, if you have almost certainly some forms of genetics make people predisposed. And then as we said in the last episode, having another neurological condition, so having migraine aura, a physical injury, an infective illness, these are powerful reasons to trigger neurological symptoms. And it's not so much why they happen. It's more why do they get there and get stuck? We all probably have transient functional symptoms actually, but why they get stuck in people with FND for various reasons to do with the way their brains work or their past experiences, or sometimes what happens to them in medical systems.

So developing a very open idea about why someone might have FND really helps you, I think, explain that back to patients and produce individual sort of formulations of the problem.

Dr. Gabriela Gilmour: Yeah. And I often say to my patients, "I don't know exactly why you, why today have this." And that's true in medicine in general. We actually often don't know why anybody develops any medical condition with a few exceptions, but we know about risk factors really.

Dr. Jon Stone: Absolutely. It's one of the reasons I hate the term medically unexplained. Actually, I think FND is perhaps more explained in some ways than some of the other conditions like multiple sclerosis and ALS that we actually deal with where we really don't know why they happen.

Dr. Gabriela Gilmour: Well, we will be back for more Neurology Minute episodes to continue our discussion on FND. Thanks for listening.