What Is a Functional Neurological Disorder?

In 2010, Gavin Martin suffered a series of injuries at his workplace. None of them were terribly serious, and they healed on their own. But Martin (not his real name), who was in his mid-20s, found that the resulting disabilities — shooting pain, weakness, and speaking difficulties — persisted. Then they began to spread.

During the next few years, Martin lost function in his vocal cords and his limbs. “At my most disabled, I was in a wheelchair, unable to walk. I couldn’t use my hands for more than grasping weakly,” he recalls. “There were months at a time when I couldn’t speak.”

His quest for a diagnosis took him to neurologists, rheumatologists, allergists, and immunologists. He visited five major medical centers, but no one could figure out what was wrong. Some of the doctors thought he might have an undiscovered genetic condition that could prove fatal, a hypothesis that only increased Martin’s alarm.

“Eventually, I ran out of places to go,” he says. “I just could not get referred anywhere else.”

In a last-ditch effort, he applied to the highly selective National Institutes of Health Undiagnosed Diseases Program, and was accepted in 2017. A team of specialists from multiple disciplines examined him.

Their diagnosis was clear: Martin had functional neurological disorder (FND).

“I think their team actually knew what I had just by looking at my application,” he says.

The FND-affected brain looks healthy on MRI studies or CT scans. But the way it communicates — with itself, the body, and the outside world — has gone awry. It’s not a “hardware” problem, as in stroke or multiple sclerosis (MS). Structurally, the brain is healthy.

Imagine the brain as a computer;
with functional neurological disorders, it’s running faulty Software.

Yet FND does represent “changes in the software circuitry of the brain,” says Jeremy Schmoe, DC, DACNB, director of the Functional Neurology Center in Minnetonka, Minn. Imagine the brain as a computer; with FND, it’s running faulty software.

Therein lies the conceptual challenge of the disease: It is rooted in the brain, but the brain is healthy; it’s a signaling problem, not a structural one.

“I hit a real emotional low point,” says Martin. “I thought they were saying I had a delusion of illness — like I had inflicted it on myself or there was no substantial disability beyond me thinking that I had one. It was incredibly unnerving.”

Yet as Martin researched FND, he started to understand the condition in a new way. He also gained access to emerging insights and treatments that have made a world of difference to his recovery.

Complicated Signals

Through the centuries, FND has been given various names, including “conversion disorder” and “hysteria.” Stigma has often followed it.

“People thought these patients were constitutionally weak, exaggerating their symptoms, or making it up,” says London-based psychiatrist Alastair Santhouse, MA, FRCP, FRCPsych, author of Head First: How the Mind Heals the Body. “We have a far more sophisticated understanding now of what this is. These symptoms are not made up or imagined.”

Symptoms of FND can include weakness or paralysis, abnormal movements, changes in speech, difficulty swallowing, seizures, numbness, and sensory challenges, such as difficulty seeing, smelling, or hearing. Many of these symptoms are also present in other neurological conditions, such as Parkinson’s, MS, epilepsy, or stroke, but the underlying causes are different.

Back when it was known as conversion disorder, FND was thought of as a diagnosis of exclusion, made only when tests had ruled out all other possible diseases. The diagnosis also required a connection to a psychological stressor.

“It was thought that some psychic distress was being converted into a physical symptom,” explains Santhouse. For instance, if someone had seen something upsetting, the belief was that they might develop blindness in response.

But functional symptoms are rarely that literal. And although many people diagnosed with FND do have a history of traumatic or stressful life events, not all do.

Different brain areas communicate in a way that allows us to move around and think and sense things.” When someone has an illness, injury, or upsetting experience, it can change the way these brain areas talk to each other.

Neurologists can now confidently diagnose FND using specific neurological examination features, says David Perez, MD, MMSc, director of the Functional Neurological Disorder Clinical Unit and Research Program at Massachusetts General Hospital. By the time the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) was published, in 2013, the disorder had been reframed as a “rule-in” diagnosis — which means a specific list of criteria must be met rather than ruled out — and renamed FND.

Some of the positive signs used to diagnose FND include Hoover’s test for functional weakness, in which a person may have significant weakness in one leg when they consciously try to move it but find that their strength returns to normal when movement is triggered in a different way. Or someone might be unable to walk or turn, but if they’re distracted, mobility returns.

Estimating the prevalence of FND is challenging because of how the definition has changed over time. But a 2010 multicenter study in Scotland found that functional/psychological disorders were the second most common diagnosis category in outpatient neurology clinics, behind only headaches. And an investigation published in JAMA Neurology in 2021 estimated annual spending for FND-related emergency-room visits and inpatient care to be more than $1.2 billion per year.

FND and the Brain

“FND is a condition that lives at the intersection of neurology and psychiatry,” explains Perez. It falls under a larger category of hybrid brain–mind–body conditions that are often referred to as functional disorders — a category that can include conditions such as irritable bowel syndrome (IBS) and fibromyalgia, which are distinguishable mainly in their effects.

Functional disorders are contrasted with “organic” diseases, such as MS or cancer, which are diagnosed based on biological changes in the body.

What makes FND unique is the way it rewires the brain to produce neurological symptoms. In FND, the amygdala (part of the limbic system that’s involved in the stress response) is hyperactive, while the brain’s frontal lobe (which plays a role in calming the amygdala) is underactive, explains Stanford University neuropsychiatrist Sepideh Bajestan, MD, PhD.

“This is what we see in PTSD and panic disorder also,” she says. But in types of FND that involve abnormal movements, the limbic system is also hyperconnected to the parts of the brain that control movement. This means that bodily movement can be affected by current or even past stresses. (Imagine the way your hands might involuntarily shake after narrowly avoiding an accident. Now imagine if that state didn’t pass.)

Functional ­symptoms for which no ­physical cause can be found — headaches, stomach­aches, back pain, ­fatigue, dizziness, or chest pain — are ­incredibly common.

“Think of the brain as an ensemble,” says Martin. “Different brain areas communicate in a way that allows us to move around and think and sense things.” When someone has an illness, injury, or upsetting experience, it can change the way these brain areas talk to each other.

“Certain parts of the brain, like the amygdala, can influence the operation of everything else because they’re highly interconnected with other parts of the brain,” he explains. “All of a sudden you have one part of the brain that’s yelling at everyone else, and the other parts of the brain respond to that.”

Functional symptoms for which no physical cause can be found — headaches, stomachaches, back pain, fatigue, dizziness, or chest pain — are incredibly common. In one study, a physical cause was shown in only 16 percent of the 567 new complaints of common symptoms presented to U.S. primary-care practices over a three-year period.

Anyone who has experienced a tension headache or nervous stomach in a stressful moment knows that our emotions can lead to physical symptoms. “The difference between FND and some other more passing functional symptoms is that in FND, these patterns get stuck,” says Martin. “The brain has the ability to learn and change, and sometimes it doesn’t go back.”

Functional disorders like fibromyalgia are likely driven by at least some different mechanisms than FND. But commonalities that might underlie the broader category of brain–mind–body conditions are an active area of research. “A subset of patients with FND also have fibromyalgia or IBS — what we think of as functional somatic disorders,” Perez says. “The increased coexistence of these conditions in one population potentially suggests some shared mechanisms.”

This means that as research into FND progresses, people suffering from other chronic brain–mind–body disorders also stand to benefit. Advances in understanding FND also start to erase the often arbitrary distinction between mental and physical health, he notes.

“In fact, maybe with the challenges of the pandemic and everything else going on, we’re realizing that physical health and mental health are interconnected — that one’s mental health is one’s physical health.”

Risk Factors and Triggers

For FND, Perez says, it’s important to investigate potential risk factors and triggers that can also perpetuate the disorder. Yet, for each patient, these elements might be unique and interact differently.

Adverse early life experiences, such as abuse or neglect, can be a risk factor for FND. So can a history of depression, anxiety, and trauma symptoms. But these are far from universal among FND patients, and an assumption of their centrality to the condition has contributed over the years to neglected and misunderstood patients.

“Some FND patients do not report adverse life experiences and have never been in therapy,” Perez says. “They’re used to pushing through and doing 120 percent. For reasons that might be personal to each case, that person with high-achieving tendencies can also develop FND.”

Returning to the brain-as-computer analogy, Perez notes that there are many ways that software can crash. “That’s why a one-size-fits-all formulation falls flat in the FND population.”

FND tends to be triggered by something that draws attention to the body. That might be a common event, such as a minor physical injury, a viral illness, or even a vaccination. “The physical triggering event is usually something that would be expected to get better,” explains St. George’s, University of London, neurologist Mark Edwards, PhD, on the website FND Hope.

“Some FND patients do not report adverse life experiences and have never been in therapy,” Perez says. “They’re used to pushing through and doing 120 percent. For reasons that might be personal to each case, that person with high-achieving tendencies can also develop FND.”

“For example, a flu that would be expected to go [away] after a few days’ rest, but instead symptoms continue and functional symptoms emerge. Sometimes this process can be very quick and dramatic or sometimes much slower.”

It’s not the injury, illness, or event itself that triggers FND, but the attention, awareness, emotion, and meaning-making that accompanies it. If someone has an injury to their leg, they might then fixate on it, says Santhouse. “They notice the sensations in that part of the body, they’re hesitant to use it, and the symptom develops further. By the time you see them in the clinic, they may already be walking with a limp or using walking aids.”

Paying attention to the body is not inherently dangerous, notes Martin. But attention can amplify signals and give form to ambiguous feelings in a way that isn’t always helpful. “Imagine I’m walking through a field and feel the tickling of the grass on my legs, and I suddenly encounter a spider and it freaks me out: In the future, my brain at a subconscious level will be more likely to associate the ambiguous feeling of grass on my legs with the presence of a spider.”

In this way, FND isn’t caused by physical or psychological factors alone, but by the way they interact in the brain. “They’re both converging on a common system in the brain, where all these things are processed together. To some extent, they become indistinguishable,” he explains.

This process is not voluntary and can result in symptoms that are very real. It also helps explain why postconcussion patients or people with “organic” neurological disorders such as Parkinson’s, epilepsy, or MS are particularly vulnerable to developing functional-neurological symptoms in addition to those caused by their primary condition.

As Martin describes it, “The brain learns the injury, absorbs it, and then reenacts it.”

“We are not talking about personal flaws or weak-willed patients wishing to be sick,” Perez stresses. This understanding is crucial for providers to deliver a diagnosis of FND clearly and empathetically — and to point patients toward helpful treatments.

Treating FND

Educating patients about FND is the first step in treating it. “The starting point is to come to a shared understanding of what’s causing the symptoms,” Santhouse says. “Then you can start to treat them.”

Like many chronic conditions, FND benefits from a multidisciplinary approach. “The two mainstays of treatment are physical rehabilitation — including physical therapy, occupational therapy, and/or speech and language therapy — coupled oftentimes with psychotherapy,” Perez says.

For Martin, the most successful treatment was physiotherapy that got him out of his wheelchair, and then off a cane, until he was walking normally again. He has also benefited from mind–body techniques, such as body scanning, awareness exercises, and progressive muscle reaction, and an app to help deal with chronic pain.

Physiotherapists can also work with patients to retrain particular movements, usually using some kind of diversion so the patient isn’t actively focusing on the body part in question.

For instance, some patients who can’t walk as they once did are able to run or walk on a treadmill. Using music or automatic movements from learned dances can also help improve movement.

Researchers conducting a pilot trial of 60 patients who’d had FND symptoms for more than six months found that after five days of specialized physiotherapy intervention, 72 percent of patients reported symptom improvement, compared with 18 percent of patients in the control group who received standard physiotherapy.

The combination of movement retraining, cognitive behavioral therapy, and limiting overwhelming stimuli was transformative for Martin. (For some FND patients, symptoms are triggered by sensory overstimulation — a hypersensitivity that’s like what people with autism experience: Lights can feel too bright, touch can be uncomfortable or painful, and smells or sounds can feel overpowering.)

“It took time and many false starts, but my symptoms began to stabilize, and then to recede,” Martin recalls. “I found I could walk for longer and work more consistently, and I felt less pain. When a limb started to twitch, I’d pull my attention off it, occupy myself with other movements, or moderate my pain with deep breaths.”

In 2018, he had more than 150 days of headache and was hospitalized multiple times. In 2019, the benefits of his persistent healing work became evident — he had only three headaches and recovered at home.

Perez says that patients with FND have reason for hope, but he also cautions that more research into additional therapeutic interventions is needed. “Out of the first 100 patients that come through our clinic, about 40 to 50 percent saw at least some degree of improvement. A similar 50 percent or so continue to be significantly impaired by their FND.”

Schmoe finds that some of his FND patients benefit from hypnosis and eye movement desensitization and reprocessing (EMDR) — practices that aim to access and calm deep limbic areas of the brain.

And interest is growing in the potential of psychedelics to treat a range of challenging neuropsychiatric conditions, including FND. (Research on the use of psychedelics to treat FND is ongoing in the United Kingdom.)

Other potential novel therapies might include neuromodulation (such as vagus-nerve stimulation) or transcranial magnetic stimulation, which uses magnetic fields to stimulate nerve cells in the brain.

“Patients with FND keep us on our toes in a variety of ways. A rich and varied toolkit is likely to be needed.”

Building an evidence base for effective treatments is challenging for conditions, such as FND, that benefit most from highly individualized treatments, Perez notes. “Patients with FND keep us on our toes in a variety of ways. A rich and varied toolkit is likely to be needed.”

Much work remains to be done for people with functional seizures, which have proven tough to treat. But here, too, there are hopeful signs. A recent small pilot study of children with functional seizures trained those patients to reinterpret their body signals and engage in movements to counteract the onset of seizures. Every one of the kids in the treatment group was seizure-free after one week, and 82 percent remained seizure-free two months later.

For now, FND treatment can be difficult to access, with only a limited number of multidisciplinary centers and specialized clinics. Perez hopes that eventually all major neurology outpatient clinics will be able to offer integrated, multidisciplinary care, not only for FND, but for a range of brain-based conditions across neurology and psychiatry.

Martin envisions a day when it won’t take specialists to offer this kind of support. “A sports-medicine clinic already has physical and occupational therapists, sometimes an osteopath, and sometimes a physiatrist,” he notes. (Physiatrists are physicians who specialize in rehab involving the brain and spinal cord.)

“If those people were able to offer psychologically informed treatment as well, then we could see FND treatment in the community.” (Martin shares emerging insights into FND on Twitter under the handle @FndPortal.)

Today, Martin has recovered more than most people with FND. He still has weakness in his arms and legs, plus occasional headaches and voice problems. But his symptoms have receded enough that they no longer dominate his days.

“FND is still there,” he says. “But I’ve carved out enough recovery that I can live my life again.”

This article originally appeared as “Understanding Functional Neurological Disorders” in the January/February 2023 issue of Experience Life.