Functional Neurological Disorder Symptoms: What They Are and Why They Happen
Author:
Blossom Editorial
Functional neurological disorder (FND) is a condition in which the nervous system produces genuine, at times disabling neurological symptoms, such as weakness, tremors, seizures, or vision changes, without the structural damage or disease that typically causes such symptoms.
The symptoms are real, not imagined or exaggerated, and current research suggests they arise from a problem in how the brain processes and regulates movement, sensation, and other functions, rather than from tissue damage.
FND is more common than many people realize and is frequently misunderstood or misdiagnosed. Understanding the range of symptoms, how they develop, and what effective treatment looks like can help people with FND get appropriate care sooner.
Key Takeaways
FND symptoms are real and often disabling: The condition is not imagined, exaggerated, or intentionally produced. Functional neurological symptoms reflect genuine disruption in brain functioning and can be as severe as those caused by structural neurological conditions.
FND is more common than many neurological conditions: This is one of the most common conditions encountered in neurology clinics and accounts for 5-10% of outpatient neurology consultations. It affects people of all ages and backgrounds, though it is more commonly diagnosed in women.
Treatment is available and effective: A multidisciplinary approach including physiotherapy, psychotherapy (particularly cognitive-behavioral therapy), and patient education produces meaningful improvement in many people with FND.
What is Functional Neurological Disorder?
FND is referred to as conversion disorder or functional neurological symptom disorder in the DSM-5, though the term FND is increasingly preferred in medical practice as it better reflects current understanding of the condition.
Although FND is a neurological condition, psychological factors such as stress, trauma, and mental health conditions may contribute to its development and maintenance in some individuals. However, the exact cause of FND remains unknown.
According to the National Institute of Neurological Disorders and Stroke, FND results from a disruption in the way the brain sends and receives signals, not from damage to the brain's structure. This is why conventional scanning, such as MRIs, which measure changes in brain structure, can come back perfectly normal for people with FND.
Modern neuroimaging research has identified differences in patterns of brain activity and connectivity in people with FND, supporting its legitimacy as a neurological condition, although these findings are not currently used to diagnose the condition.
Crucially, a diagnosis of FND is not made simply by ruling out other conditions (diagnosis by exclusion). Neurologists rely on a patient’s symptoms, history, and physical exam to look for positive clinical signs characteristic of FND.
Common Functional Neurological Disorder Symptoms
FND can produce a wide range of symptoms affecting movement, sensation, consciousness, and cognition. Symptoms often vary in intensity over time and may be influenced by attention, distraction, and stress. The following are the most commonly reported symptom categories.
Motor Symptoms
Motor symptoms are among the most common presentations of FND. They include:
Functional weakness or paralysis: Loss of strength in one or more limbs that does not correspond to a specific nerve or brain lesion pattern. People may report feeling that the limb doesn’t belong to them. They may be unable to move a limb voluntarily but show normal muscle activation in certain conditions. Functional weakness can affect many muscle groups at the same time, unlike those caused by an injury or stroke, which affect specific groups.
Functional tremor: Involuntary shaking that typically has features distinguishing it from neurological tremors, for instance, when the person is asked to copy an external rhythmic movement using the better hand, the tremor in the other hand ceases or synchronizes to that rhythm. Tremors that increase or move to another body part when the one with the tremor is immobilized can be functional.
Functional dystonia: Abnormal postures or muscle contractions, most commonly affecting the foot, ankle, fingers, or wrists, that are fixed and may cause significant disability and pain.
Gait disturbances: Unusual walking patterns such as excessive slowness, buckling, dragging, or jerky movements that are characteristic of FND rather than structural pathology.
Facial movements: Functional tics, spasms, or abnormal facial movements.
Seizure-Like Symptoms (Functional Seizures)
Functional seizures, also called non-epileptic attack disorder (NEAD) or dissociative seizures, are episodes that resemble epileptic seizures but are not associated with the abnormal electrical brain activity characteristic of epilepsy. They are among the most studied presentations of FND.
Features of functional seizures may include long duration (greater than 90 seconds), eyes closed during the episode but retaining memory of the event, side-to-side head or body movement, asynchronous movements, pelvic thrusting, ictal (mid-seizure) crying, and absence of postictal (post-seizure) confusion. These features may also help to distinguish functional seizures from epileptic seizures, although no single feature is diagnostic by itself.
Diagnosis typically requires video-EEG monitoring, which is considered the gold standard when the diagnosis is uncertain, although diagnosis may sometimes be made based on clinical assessment and supporting evidence. NICE guidelines recommend specialist assessment for all suspected functional seizures.
Sensory Symptoms
FND commonly affects sensation in ways that do not correspond to anatomical nerve distributions. Common sensory symptoms include:
Numbness or tingling affecting unusual distributions, such as one half of the entire body
Visual symptoms, including blurred vision, double vision, or visual field loss
Hearing changes or functional deafness
Speech and swallowing difficulties, including functional aphonia (loss of voice), stuttering, and foreign accent syndrome
Functional dizziness, also called persistent perceptual postural dizziness (PPPD), is triggered by upright posture, active or passive motion, or moving visual stimuli
Although not a part of the DSM-5 criteria for FND, altered pain perception, including widespread pain or hypersensitivity, is a common comorbidity. The pain can appear as chronic fibromyalgia, chronic spinal pain, migraine, or complex regional pain.
Cognitive and Dissociative Symptoms
Cognitive symptoms are common in FND and can be as disabling as motor or sensory symptoms. These include difficulties with memory, attention, and mental processing speed. Dissociative symptoms are also frequent, including feelings of unreality, depersonalization (feeling detached from oneself), and derealization (feeling that the environment is unreal).
A recently published review in Current Opinion in Psychiatry notes that functional cognitive disorders affect 40-70% of people with FND and that people with these symptoms tend to describe severe cognitive impairment while continuing to perform cognitively demanding work. This inconsistency or mismatch in symptoms is considered a positive diagnostic feature of functional cognitive disorder.
Moreover, functional cognitive disorder differs from neurodegenerative disorders like dementia in that its symptoms are generally stable and non-progressive.
What Causes Functional Neurological Disorder?
The exact mechanisms behind FND are not fully understood, but research has advanced significantly in recent years. Current models emphasize that FND is a disorder of the brain's predictive and active inference systems. This means that the brain generates symptoms based on strong predictions about how the body should be functioning, overriding accurate sensory feedback.
For instance, in functional leg weakness, the brain wrongly predicts that a limb isn’t there, which overrides the sensory input that it is still present. This results in heaviness, weakness, or paralysis in the leg.
While causative factors of FND are not established by research, the following factors are closely associated with the neurological condition:
Trauma and adverse life events: A history of physical or psychological trauma, both recent and childhood, is more common in people with FND than in the general population, though it is absent in a significant proportion of cases.
Comorbid mental health conditions: Anxiety disorders, depression, and PTSD are more common in people with FND, though FND is not simply a manifestation of anxiety, and many people with FND have no significant psychiatric history.
Neurobiological vulnerability: Research suggests alterations in how the brain processes interoception, predictive coding, and emotional regulation may predispose certain individuals to FND. Functional neuroimaging studies show differences in brain networks between people with functional tremors and those making voluntary tremors, confirming that FND is associated with changes in how the brain networks work together.
Precipitating events: FND often has an identifiable onset trigger, such as a physical injury, illness, surgery, or acute stress, that may establish an abnormal pattern of nervous system functioning.
How is FND Diagnosed?
Diagnosis of FND should be made by a neurologist who is familiar with the condition. It requires identifying positive signs consistent with FND while considering and evaluating alternative neurological explanations when appropriate. This typically involves a neurological examination, brain imaging via EEG, and other investigations depending on the presentation.
Common positive clinical signs used in diagnosis include the Hoover sign for leg weakness (involuntary hip extension when the opposite leg is lifted), the tremor entrainment test, and the change of symptoms with distraction. These are not trick tests; they reveal whether involuntary control systems use voluntary pathways, a characteristic feature of FND.
Treatment for Functional Neurological Disorder
FND is treatable, and many people experience significant improvement. Treatment is most effective when delivered by a multidisciplinary team and tailored to the individual's specific symptoms and contributing factors.
Physiotherapy and Rehabilitation
Specialist physiotherapy is considered a core treatment for FND, particularly for motor symptoms. FND-specific physiotherapy focuses on retraining movement patterns and addressing the excessive attention given to physical symptoms that can perpetuate them.
A randomized controlled trial published from 2017 found that physiotherapy specifically designed for FND significantly improved motor symptoms and disability in 72% of FND patients compared to 28% of those treated with standard physiotherapy.
Although no specific guidelines regarding duration and frequency of physiotherapy treatment are available, one 2023 review on physical rehabilitation of FND suggests a minimum of five treatments per week for inpatient care, a weeklong rehabilitation program for outpatients, and a minimum of 24 telehealth sessions produce substantial improvements.
Psychotherapy
Cognitive-behavioral therapy (CBT) adapted for FND addresses the psychological and behavioral factors that maintain symptoms, including illness beliefs, avoidance behaviors, and the relationship between symptoms and emotional states.
While not all people with FND may have mental health problems like anxiety or panic disorder, in those with psychological comorbidities, it may be essential to treat these first before starting physical therapy.
Evidence for CBT in FND is growing, with positive findings particularly for functional seizures. Trauma-focused therapies may be appropriate when unprocessed trauma is a significant contributor.
Education and Self-Management
Providing a clear and validating explanation of the diagnosis is considered an important part of treatment and may improve engagement and outcomes. Creating an awareness of FND by sharing its positive diagnostic features instead of focusing on what is is not helps patients recognize it as a genuine neurological disorder.
Research suggests that patients who receive an accurate diagnosis with adequate explanation show better outcomes than those who are dismissed or given no diagnosis.
FND and Mental Health
Mental health conditions are common in people with FND, though they are not universal and are not the "cause" of the condition in a straightforward sense. Anxiety and depression affect a significant proportion of people with FND, partly as a consequence of living with a disabling, often misunderstood condition, and partly because of shared neurobiological vulnerabilities.
A psychiatrist can be an important part of the treatment team for people with FND, particularly when anxiety, depression, or trauma are contributing to symptom persistence. Blossom Health offers virtual psychiatric care covered by in-network insurance. Getting started takes only a few minutes.
Medical Disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition. If you are experiencing a mental health crisis, contact the 988 Suicide and Crisis Lifeline by calling or texting 988.
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