Jennifer Brown, M.S.
Psychology Ph.D. student
JFK School of Psychology and Social Sciences
National University
Functional Neurological Disorder (FND) is a common condition seen in both neurology and psychiatry, with research listing it as the second most common reason individuals are referred to neurology, making up approximately 5-10% of new neurology consults each year (Bennett et al., 2021; Mavroudis et al., 2024). Nevertheless, research on its true prevalence varies, with studies ranging from 4-10/100,000 new cases each year in general civilian populations and 29.5/100,000 new cases in military populations (Bennett et al., 2021; Garrett et al., 2020; Perjoc et al., 2023). According to the National Organization for Rare Disorders (2024), FND is a rare disease that the medical community has struggled to grasp an understanding of and how to treat. That said, understandings of FND in both the medical and psychiatric communities have been historically based on theories that link symptoms to psychological pathologies such as hysteria, dissociative symptoms, stress reactions, and trauma responses, which may not always be relevant in every case (Bennett et al., 2021; Mavroudis et al., 2024; Raynor & Baslet, 2021). Consequently, uncertainty in FND’s etiology has resulted in myths and misconceptions that the general public may understand about those with the condition. The following article was created to help clarify what providers currently understand about FND and to debunk some of its common myths and misconceptions.
What is Functional Neurological Disorder?
Per FND Hope (2021), the world’s first and only global charity and leading organization for FND, Functional Neurological Disorder (FND) is a health condition in which the nervous system improperly sends and receives signals to the brain and (FND Hope, 2021d; National Organization for Rare Disorders, 2024). The exact cause of neurological symptoms in patients with FND is unclear. However, it is believed that FND affects the nervous system’s functioning, leading to a disconnection in how the brain signals movement, cognition, and sensation and how the body responds to these signals (National Institute for Neurological Disorders and Stroke, 2024).
Since FND is associated with both neurology and psychiatry, it is included in the Diagnostic and Statistical Manual of Mental Disorders (5th edition, text-revision) and the ICD-11. Previously, FND was known as conversion disorder, a disorder rooted in the psychoanalytic theory that unconscious psychic conflict is “converted” into physical and neurological symptoms (APA, 2022, p. 509). However, the DSM currently recognizes the condition as “Functional Neurological Symptom Disorder (Conversion Disorder),” as a neuropsychiatric disorder that involves motor symptoms, abnormal movements, sensory symptoms, dystonia, diplopia, and episodes of unresponsiveness that mimic seizures or syncope (American Psychiatric Association, 2022).
What are the Types of FND?
FND typically presents as one of two types: functional movement disorder or functional seizures (previously called psychogenic non-epileptic or dissociative seizures) (APA, 2022, p. 509; NINDS, 2024). For any subset of FND to be diagnosed, providers must find clear evidence of incompatibility between a patient’s symptoms and those associated with organic neurological disorders (APA, 2022, p. 509; Bennett et al., 2021). The challenge to this is that not every case of FND is readily detectable, and patients misdiagnosed with other conditions may encounter delays in diagnosis and treatment. Bennett et al. (2021) recommends that providers should not base diagnosing FND solely on psychiatric features or recent stress, regular examinations and tests, and the misinterpretation of abnormal tests.
Can Tests Positively Detect FND?
Specific tests can sometimes be done to positively rule in FND. For example, providers can differentiate between organic and functional weakness in functional limb weakness cases by testing for Hoover’s sign and hip abductor sign. Positive Hoover’s and hip abductor signs reliably show internal inconsistency between voluntary and autonomic movements, which are present in functional movement disorders (Bennett et al., 2021). Likewise, in episodes resembling epileptic seizures, providers can differentiate between epilepsy and functional seizures by the length of seizures, asynchronous movements, body or head movements, closed eyes, and memory of event; however, video electroencephalographs (EEGs) are considered the gold standard in making clear distinctions (Bennett et al., 2021; Mavroudis et al., 2024).
What are the Symptoms of FND?
Patients with FND can have a wide range of neurological and sensory symptoms, including gastrointestinal issues, chronic pain, cognitive, sensory, and visual changes, gait and balance issues, headaches and migraines, paralysis and weakness, sleep and speech problems, and functional (non-epileptic) seizures (Bennett et al., 2021; FND Hope, 2021d; NINDS, 2024). Research on FND has shown that symptoms and their severity and intensity can vary between patients (Mavroudis et al., 2024). Bennett et al. (2021) describe functional limb weakness involving stroke-like symptoms, which can disturb or alter sensations in a limb. Additional movement-related symptoms associated with FND include tremors, dystonia of the face, ankle, or hand, jerking, and gait disturbances (Bennett et al., 2021; Mavroudis et al., 2024).
The sensory component of FND often entails numbness, tingling, pins and needles, burning, electric shock-like pain, visual loss, and diplopia, which may or may not be related to proprioception (Mavroudis et al., 2024; NINDS, 2024; Perjoc et al., 2023). Accordingly, the cognitive symptoms of FND include a wide variety of impairments, such as memory problems, difficulty retaining and recalling information, attention deficits, issues with word-finding and producing speech, and difficulty making decisions (Mavroudis et al., 2024; NINDS, 2024). Finally, in those with functional seizures, patients tend to experience long duration of shaking or body movement, syncope-like episodes, dissociation, and panic-attack-like episodes (Bennett et al., 2021; NINDS, 2021).
What is the Difference Between Other Neurological Conditions and FND?
Compared to other neurological disorders, FND does not have an organic cause; instead, the most up-to-date research classifies FND as a functional problem between the brain and body (FND Hope, 2021d). Since symptoms are not from organic disease, standard tests and examinations are often expected to be negative in FND patients, while standard testing in recognized neurological conditions detect structural abnormalities (Begue et al., 2019). In other words, recognized neurological diseases are better understood and treated by neurology providers than functional disorders like FND.
What Causes FND?
The exact cause of dysfunction in the nervous system is unknown. However, researchers believe that the functioning of primary physiological processes becomes altered in those with FND (Perjoc et al., 2023). Specifically, neurobiological factors such as neurotransmitter abnormalities, inflammatory markers, and neuroplasticity may impact the nervous system in those with FND (Mavroudis et al., 2024). Moreover, psychological factors such as stressful events, adverse childhood experiences, maladaptive cognitions, and environmental factors like societal attitudes may also contribute to dysfunction (Mavroudis et al., 2024). Similarly, functional and/or structural abnormalities related to emotional and predictive processing and reductions may also explain functional deficits in FND (Perjoc et al., 2023). Research has additionally found that increased limbic and paralimbic activity, altered amygdala habituation and sensitivation, self-agency disturbances, and increased connectivity between emotional processing and motor control may influence functionality (Mavroudis et al., 2024).
Is FND Solely a Psychological Issue?
Currently, the DSM-5 terms FND as Functional Neurological Symptom Disorder, classifying it as a neuropsychiatric disorder (APA, 2022). That said, FND has both neurological and psychological components that can influence each other. Some FND patients have comorbid neurological conditions, while some have mental health conditions such as depression, anxiety, and post-traumatic stress disorder, which may trigger or worsen functional symptoms (Hallett et al., 2023). Accordingly, some patients have both neurologic and psychiatric conditions with FND (Hallett et al., 2023). However, it is essential to note that psychological factors do not always affect patient symptomology; individuals can still have FND without a history of psychological trauma or mental illness (FND Hope, 2021a). Leading research organizations posit that symptoms may also occur in some cases due to undiagnosed and/or untreated medical condition s (FND Hope, 2021d). However, more research is needed in this area to better understand this phenomena.
Are Symptoms Voluntary?
FND symptoms can be mistaken as voluntary in cases where symptoms do not resemble typical neurological conditions. Nevertheless, functional symptoms are involuntary and are not produced by patients by their own will or under voluntary control (FND Hope, 2021a). Research has found that self-agency and multimodal integration are often disrupted in FND patients (Mavroudis et al., 2024). Specifically, neuroimaging studies have shown that brain activations when voluntary control is perceived as altered show disruptions in FND patients (Mavroudis et al., 2024). Additionally, research also suggests that hypersensitive amygdala responses during injury or panic may produce similar sensations and movements as in FND, and are perceived as involuntary (Mavroudis et al., 2024).
How is FND Treated?
Depending upon patient symptoms, patients can improve with different types of multidisciplinary treatments. Patients may benefit from cognitive behavioral therapy, physiotherapy, physical therapy, short-term motor retraining, occupational therapy, speech therapy, and pharmacological treatments as well as hypnotherapy, biofeedback, and therapies to help manage pain (FND Hope, 2021c; Mavroudis et al., 2024). Furthermore, patients know themselves and their body the best, thus, over time are able to identify triggers to symptoms and the best management techniques to help reduce symptoms and flare-ups.
Ultimately, the best way to help improve patient outcomes is by not delaying treatment and incorporating multidisciplinary team in a patient’s care (FND Hope, 2021c). Psychology, psychiatry, and neuropsychology/neuropsychiatry, primary care physicians, neurologists, occupational and physical therapists, and physiotherapists should come together to help create supportive treatment plans for those with symptoms of this disorder, as FND has no cure. Knowledge of this condition should be readily available so that patients are aware of signs and symptoms of FND to differentiate a functional problem versus an organic disease. Despite uncertainty in etiology, patients have the right to access services and to be heard and understood by providers.
Providers and patients can learn more about the condition by accessing FND Hope’s website at https://fndhope.org. FND Hope provides patients and providers with the most up-to-date information, resources, and research, including symptoms and treatment options, provider listings of those who treat FND, and provider education on the condition.
References
American Psychiatric Association. (2022). Somatic and related disorders. In Diagnostic and Statistical Manual of Mental Disorders (5th ed., text revision). https://doi.org/10.1176/appi.books.9780890425787
Begue, I., Adams, C., Stone, J., & Perez, D. L. (2019). Structural alterations in Functional Neurological Disorder and related conditions: A software and hardware problem? NeuroImage: Clinical, 22: 101798. https://doi.org/10.1016/j.nicl.2019.101798
Bennett, K., Diamond, C., Hoeritzauer, I., Gardiner, P., McWhirter, L., Carson, A., & Stone, J. (2021). A practical review of Functional Neurological Disorder (FND) for the general physician. Clinical Medicine (London, England), 21(1), 28-36. https://doi.org/10.7861/clinmed.2020-0987
FND Hope. (2021a). 10 Myths about Functional Neurological Disorder. https://fndhope.org/fnd-guide/10-myths-about-fnd/
FND Hope. (2021b). Symptoms. https://fndhope.org/fnd-guide/symptoms/
FND Hope. (2021c). FND Treatments: Patients benefit the most from multidisciplinary treatment. https://fndhope.org/fnd-guide/treatment/
FND Hope. (2021d). What is FND: FND is a problem with how the brain and body send and receive signals. https://fndhope.org/fnd-guide/
Garrett, A. R., Hodges, S. D., & Stahlman, S. (2020). Epidemiology of functional neurological disorder, active component, U.S. Armed Forces, 2000-2018. MSMR, 27(7), 16–22.
Mavroudis, I., Kazis, D., Kamal, F. Z., Gurzu, I., Ciobica, A., Pădurariu, M., Novac, B., & Iordache, A. (2024). Understanding Functional Neurological Disorder: Recent insights and diagnostic challenges. International Journal of Molecular Sciences, 25(8), 4470. https://doi.org/10.3390/ijms25084470
National Institute for Neurological Disorders and Stroke. (2024). Functional Neurological Disorder. National Institute of Health. https://www.ninds.nih.gov/health-information/disorders/functional-neurologic-disorder
National Organization for Rare Disorders. (2024). Functional Neurological Disorder. https://rarediseases.org/rare-diseases/fnd/
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Perjoc, R., Roza, E., Vladacenco, O. A., Teleanu, D. M., Neacsu, R., & Teleanu, R. I. (2023). Functional Neurological Disorder–Old problem new perspective. International Journal of Environmental Research and Public Health, 20(2), 1099. https://doi.org/10.3390/ijerph20021099
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