Functional Neurological Disorder (FND): Symptoms, Causes, and Treatment
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If you have ever sat in a neurologist's office and heard the phrase "everything looks normal on the scan" while watching someone you love struggle to walk, speak, or control their movements, you already understand the core frustration of Functional Neurological Disorder.
FND is real. The symptoms are real. The disability is real. The fact that standard imaging does not show a structural lesion does not mean nothing is wrong. It means the problem is in how the brain is functioning, not in the physical structure of the brain tissue itself.
This distinction matters enormously, and it is frequently missed, minimized, or communicated poorly by the clinicians families trust most.
What Functional Neurological Disorder Actually Is
Functional Neurological Disorder is a condition in which the brain produces genuine neurological symptoms due to disrupted signaling and network function rather than structural damage. According to a landmark 2022 review by Hallett, Aybek, Dworetzky, McWhirter, Staab, and Stone published in The Lancet Neurology, FND involves abnormal patterns of brain network activity, particularly in regions governing movement, attention, and sensory processing.
The National Institute of Neurological Disorders and Stroke classifies FND as a disorder of brain function rather than brain structure. This is not a soft distinction. It reflects a fundamental shift in how neuroscience understands the condition, one that has been decades in the making and is still catching up to clinical practice.
FND falls under the VA's diagnostic code 9424 and is listed as "Conversion Disorder/Functional Neurological Disorder." It is one of 31 mental health-related conditions the VA considers eligible for service-connected disability compensation, which means it is documented, recognized, and compensable in veteran populations.
What FND Looks Like
FND presents differently from person to person. Symptoms can appear suddenly, fluctuate over time, and change in character. Common presentations include:
- Tremors or uncontrolled shaking
- Functional limb weakness or paralysis
- Difficulty walking or sudden gait changes
- Non-epileptic seizures (also called functional seizures or previously called psychogenic non-epileptic seizures)
- Speech difficulties including slurring or loss of voice
- Sensory disturbances such as numbness or altered sensation
- Cognitive symptoms including memory difficulties and brain fog
- Chronic fatigue
- Vision changes
One of the features that most confuses both families and clinicians is that symptoms can be inconsistent. A person may walk steadily in one moment and be unable to stand in the next. This inconsistency is not evidence of faking. It is a documented feature of how disrupted brain signaling works. As researchers at neurosymptoms.org, a clinical resource developed by neurologist Dr. Jon Stone at the University of Edinburgh, explain, some people with FND can also have a co-existing neurological disease. Having one condition does not rule out the other.
How FND Develops: The TBI and Trauma Connection
FND does not appear out of nowhere. Research consistently identifies a cluster of predisposing, precipitating, and perpetuating factors. For veterans and people with a history of brain injury, several of those factors are often present simultaneously.
FND symptoms can develop following traumatic brain injury, concussion, severe illness, physical trauma, or significant psychological stress. A 2024 review published in PMC examining the relationship between post-concussion syndrome and FND concluded that the two conditions should be understood along a continuum of brain dysfunction shaped by injury, psychology, and contextual factors. The review introduced the concept of a "functional overlay," meaning FND symptoms can develop on top of existing neurological injury rather than replacing it.
For veterans specifically, the picture is well-documented. Research published in Current Psychiatry Reports notes that with PTSD being the most diagnosed and highest-compensated mental health condition in the veteran population, it is not surprising that FND accompanies this diagnosis either during or after military service. A separate study published in PMC confirmed that veterans of the U.S. military are potentially at increased risk for FND due to their high exposure to stressors and trauma.
The comorbidity data further reinforces this. A 2024 systematic review found that the overall prevalence of comorbid psychiatric diagnoses in FND ranges from 51% to 95%, with depression, anxiety, and PTSD among the most prevalent. Veterans with functional seizures specifically show a high comorbid risk of PTSD.
What this means practically is that a veteran managing TBI, PTSD, and cognitive decline may also develop FND as a downstream consequence of that neurological and psychological burden. These conditions are not mutually exclusive. They coexist, interact, and compound each other in ways the medical system is still learning to recognize and treat simultaneously.
Why FND Is So Often Dismissed
This is the part families need to understand, because many of them have lived it.
FND carries one of the highest rates of stigma and clinical dismissal of any neurological condition. A 2024 review published in Brain, one of the oldest and most respected neurology journals, documented the sources of iatrogenic harm in FND, meaning harm caused by the medical system itself. Those sources include delayed diagnosis, direct dismissal by clinicians, use of stigmatizing language, and a historical association of FND with psychological weakness or exaggeration.
The term "conversion disorder," which the DSM-5 still uses alongside FND, carries decades of baggage suggesting that neurological symptoms are a psychological conversion of emotional distress. While psychological factors can be part of FND's picture, this framing has led generations of clinicians to treat FND patients as if their symptoms are not fully real, a pattern the current research explicitly challenges.
Studies show it takes an average of 8.4 years for a person with functional seizures to receive a correct diagnosis after symptom onset. Research published in emergency medicine has found that people with FND report experiencing the highest levels of discrimination and stigma from emergency department physicians compared to any other healthcare provider group.
Importantly, FND is not commonly misdiagnosed in the other direction. Research consistently shows the rate of misdiagnosis of FND as another condition has remained at approximately 4% since 1970. When a neurologist makes the diagnosis correctly, it is usually accurate. The problem is not overdiagnosis. The problem is under-recognition, delayed diagnosis, and insufficient communication with the patient and family about what the diagnosis means.
A 2025 qualitative study analyzing hundreds of patient accounts found three consistent themes in FND diagnostic experiences: epistemic marginalization, harm from diagnostic drift, and struggles for recognition. Families described feeling dismissed, morally invalidated, and left without a clear path forward.
If this sounds familiar, you are not alone and the research supports what you experienced.
How FND Is Diagnosed
FND is diagnosed by a neurologist using positive clinical signs, not solely by ruling out other conditions. This is a shift from older practice. According to Hallett and colleagues in The Lancet Neurology, the diagnosis should be made based on recognizable patterns of symptoms and clinical signs rather than waiting for all other conditions to be excluded first.
Diagnostic tools may include:
- Neurological examination looking for FND-specific signs such as Hoover's sign for functional leg weakness
- MRI or CT imaging (to rule out structural causes)
- Electroencephalography (EEG), particularly when functional seizures are part of the presentation
- Video-EEG monitoring in specialized centers
A person can have both FND and another neurological condition. Having a confirmed TBI, Parkinson's disease, or dementia diagnosis does not exclude FND. Approximately 10 to 15 percent of people with functional seizures also have epilepsy. Co-existing conditions require careful evaluation rather than assumption that one diagnosis explains everything.
Treatment: What the Research Supports
FND is treatable. Many people improve significantly with appropriate care, and outcomes are better when diagnosis and treatment begin earlier. The Lancet Neurology review emphasized that the diagnosis of FND should be understood as identifying a potentially reversible cause of disability and distress.
Evidence-supported treatment approaches include:
- Neurological physical therapy specifically designed for functional motor symptoms, which differs from standard physical therapy and focuses on retraining movement patterns
- Cognitive behavioral therapy (CBT), with the strongest evidence base for functional seizures
- Occupational therapy to support daily function and adaptive strategies
- Psychotherapy addressing trauma history, particularly relevant for veterans and others with comorbid PTSD
- Multidisciplinary care coordinating neurology, psychiatry or psychology, and rehabilitation
Not every person with FND responds to the same treatment, and treatment access remains a significant barrier. Specialized FND clinics are limited in number. Veterans may need to advocate explicitly within the VA system for referrals that address FND as a distinct condition rather than folding it under general neurology or mental health care.
What This Means for Caregivers
Caring for someone with FND is complicated by the same stigma the person with FND faces. Caregivers frequently report being doubted by medical providers, questioned about whether they are reinforcing symptoms, or left without a clear explanation of what they are actually managing.
A few things worth knowing:
FND symptoms are not under voluntary control. The research is unambiguous on this point. A 2023 paper published in Nature Reviews Neurology by Edwards, Yogarajah, and Stone addressed directly why FND is not feigning or malingering, reviewing the neurobiological evidence that distinguishes FND from deliberate symptom production.
Symptom fluctuation is part of the condition. Days when your person is functioning better do not mean they were exaggerating on worse days. Variability is documented and expected.
Your observations matter clinically. Caregivers often notice patterns, triggers, and symptom sequences that the person with FND cannot report accurately from the inside. Document what you see. Bring it to appointments. That information is diagnostically useful.
You are not causing this by paying attention to it. One outdated clinical concern was that family attention reinforces functional symptoms. Current guidance does not support withdrawing normal care and support from people with FND.
A Note on Overlapping Conditions
FND rarely appears alone in veteran populations and in people with complex neurological histories. It commonly coexists with TBI, PTSD, cognitive impairment, Parkinson's disease, and other neurodegenerative conditions. Managing several of these simultaneously is one of the most challenging clinical situations a family can face, in part because each condition is typically managed by a different specialist who may not be communicating with the others.
If your person has multiple overlapping diagnoses, advocating for coordinated care is not optional. It is necessary. Understanding each individual condition, including FND, is the foundation for asking better questions at every appointment.
Continue Learning
If you are exploring FND alongside other neurological conditions, these articles may also help:
• The Four Stages of CTE
• Cognitive Decline After Brain Injury
• Brain Injury Education Library
• Caregiver Resources and Support
Medical Accuracy Note
This article references peer-reviewed research from The Lancet Neurology, Brain (Oxford University Press), Nature Reviews Neurology, the National Institute of Neurological Disorders and Stroke, PMC, and clinical resources from the University of Edinburgh. It is written for educational purposes and does not constitute medical advice. Diagnosis and treatment of FND require evaluation by qualified neurological and medical professionals.
References
- Hallett M, Aybek S, Dworetzky BA, McWhirter L, Staab JP, Stone J. Functional neurological disorder: new subtypes and shared mechanisms. The Lancet Neurology. 2022;21(6):537-550.
- Edwards MJ, Yogarajah M, Stone J. Why functional neurological disorder is not feigning or malingering. Nature Reviews Neurology. 2023;19:246-256.
- Begue I, Adams C, Stone J, Perez DL. Structural alterations in functional neurological disorder and related conditions: a software and hardware problem? PMC. 2024.
- Carlson HL et al. Iatrogenic harm in functional neurological disorder. Brain. 2025;148(1):27-43.
- Functional Neurological Disorders in Active-Duty Military Personnel and Veterans. Current Psychiatry Reports. 2025.
- Prevalence and impact of comorbid PTSD, c-PTSD and EUPD on symptom severity in FND: protocol for a systematic review. PMC. 2025.
- Stone J. Misdiagnosis and comorbidity in FND. neurosymptoms.org. University of Edinburgh.
- National Institute of Neurological Disorders and Stroke. Functional Neurological Disorder. ninds.nih.gov.