What is Functional Neurological Disorder (FND)
Functional Neurological Disorder (FND) is a condition at the intersection of neurology and psychiatry, characterised by neurological symptoms that cannot be explained by conventional structural or pathophysiological disease processes. Individuals with FND can present with diverse and often debilitating symptoms, such as weakness, abnormal movements, and sensory changes that mimic other well-known neurological disorders like multiple sclerosis or epilepsy. Yet, unlike these structural or organic conditions, standard diagnostic testing and imaging for FND often fail to reveal a clear lesion, damage, or pathology in the nervous system. Though long misunderstood, researchers and clinicians today recognise FND as a genuine disorder, underpinned by complex interactions among biological, psychological, and social factors. This essay explores the nature of FND, its diagnostic criteria, potential causes, associated comorbidities, and approaches to treatment and prognosis, drawing on contemporary research and clinical guidelines.
Historical Context
Historically, FND has been referred to by various names, including “hysteria,” “conversion disorder,” and “psychogenic” disorders. The term “conversion disorder” derives from early psychoanalytic theory suggesting that distressing emotions could be “converted” into physical symptoms. In the 19th century, pioneering neurologists like Jean-Martin Charcot and Sigmund Freud studied cases of “hysterical paralysis” or “hysterical blindness,” which would be labelled today as FND. However, these early conceptualisations placed an excessive focus on the psychological components of FND, leading to centuries of stigma and misunderstanding surrounding the disorder.
Recognition of the possibility that psychological stressors or trauma might contribute to genuine physical changes in the nervous system spurred efforts to merge insights from neurology and psychiatry. Through advancements in neuroscience and neuroimaging in the late 20th and early 21st centuries, evidence began to accumulate that brain circuits involved in motor control and sensory processing could function abnormally, even in the absence of structural damage. This realisation helped shift FND away from purely psychological diagnoses and toward an understanding that emphasises the interplay between the mind and brain.
Defining Functional Neurological Disorder
FND involves neurological symptoms that impact the functioning of the motor and/or sensory systems. Importantly, these symptoms arise without a primary neurological disease such as a stroke, tumour, or demyelinating lesion. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) classifies FND (still often referred to as “Conversion Disorder (Functional Neurological Symptom Disorder)”) under the category of “Somatic Symptom and Related Disorders.” According to DSM-5, the hallmark criteria include:
One or more symptoms of altered voluntary motor or sensory function.
Clinical findings that provide evidence of incompatibility between the symptom and recognised neurological or medical conditions.
Symptom or deficit is not better explained by another medical or mental disorder.
Symptom or deficit causes clinically significant distress or impairment in social, occupational, or other important areas of functioning.
In practice, diagnosing FND generally requires a thorough clinical evaluation, often involving neurologists, psychiatrists, psychologists, and other healthcare professionals. The diagnostic process aims not merely to rule out other conditions but also to seek “positive signs” of FND, such as inconsistencies in physical function during formal examination versus informal observation. For example, a patient may show an inability to move a limb during a neurological exam yet use that same limb naturally at other times (a phenomenon sometimes called “collapsing weakness” or “give-way weakness”).
Clinical Presentation and Symptoms
While FND can take on myriad forms, common presentations include:
Motor Symptoms:
Paralysis or Weakness: A limb (arm or leg) may exhibit sudden and unexplained weakness or complete inability to move.
Abnormal Movements: Involuntary tremors, spasms, jerky movements, or gait disturbances that resemble those seen in Parkinson’s disease, dystonia, or ataxia.
Seizure-like Episodes (Non-epileptic attacks): Episodes can include convulsions, shaking, or unresponsiveness, but electroencephalogram (EEG) findings are typically normal, distinguishing them from epileptic seizures.
Sensory Symptoms:
Sensory Loss or Numbness: Partial or total loss of sensation in an area of the body without any identifiable nerve damage.
Visual Changes: Blurred vision or blindness without detectible disease of the eyes or optic pathways.
Hearing Changes: Hearing loss or deafness without signs of auditory system pathology.
Cognitive and Other Associated Symptoms:
Cognitive Disturbances: Concentration difficulties or memory lapses that cannot be explained by neurological tests.
Fatigue: Debilitating fatigue is often reported, impacting daily activities and quality of life.
Pain: Chronic pain syndromes like fibromyalgia can co-occur.
A person may present with more than one type of symptom simultaneously (e.g., episodes of psychogenic non-epileptic seizures (PNES) alongside limb weakness). Symptom severity can vary drastically, sometimes improving or worsening in a short time span, and can be closely linked with emotional or physical stressors.
Prevalence and Risk Factors
Prevalence estimates vary due to methodological differences across studies, but FND is not considered rare. Some estimates suggest that FND accounts for up to 16% of referrals to neurology outpatient clinics (Stone et al., 2010). While individuals of any age, gender, or background can develop FND, several risk factors have been identified:
Gender: Historically, higher diagnosis rates in women have been reported, though recent studies suggest that men are also frequently affected.
Stressful Life Events: Although not present in all FND patients, significant life stresses or traumas physical, emotional, or sexual are commonly reported.
Psychiatric Comorbidity: Depression, anxiety disorders, and post-traumatic stress disorder (PTSD) often co-occur, and these conditions can exacerbate or maintain FND symptoms.
Personality Factors: Some research indicates possible links to certain personality traits (e.g., high neuroticism), though findings remain inconsistent.
Childhood Trauma: A history of childhood adversity or trauma has been associated with a greater likelihood of developing FND in adulthood (Feinstein, 2011).
Pathophysiological Mechanisms
The precise pathophysiology of FND remains incompletely understood, but advancements in neuroimaging (e.g., functional MRI) have shed light on possible mechanisms. Unlike structural disorders like multiple sclerosis or tumour growth, FND involves dysfunction in neural circuits rather than tissue damage. Key brain regions implicated in FND include:
Cortical Regions for Motor and Sensory Control: FND symptoms may arise from disrupted connectivity between these cortical areas and higher-order executive regions that control attention, emotion, and self-awareness (Stone et al., 2016).
Limbic System and Emotion Regulation: Heightened activity in limbic regions, including the amygdala, can disrupt motor planning and sensory perception, linking emotional distress to physical symptom manifestation.
Motor Intention vs. Motor Execution: Research suggests an impairment in the neural signals that transform the “intention” to move into the actual motor command, creating a mismatch between what the brain “wants” to do and what the body actually does (Edwards et al., 2012).
What emerges is a biopsychosocial model of FND: innate vulnerability and genetic predisposition could interact with psychological factors like stress or trauma, resulting in physiological changes in brain circuitry. Over time, reinforced patterns of disordered signalling along with the patient’s beliefs, emotional responses, and learned physical reactions, may perpetuate the disabling symptoms.
Diagnostic Process and Challenges
Positive Diagnostic Signs
Traditionally, FND was often diagnosed by exclusion, only after ruling out all possible organic causes. However, contemporary practice encourages identification of “positive” clinical signs of FND that increase confidence in the diagnosis. Examples include:
Hoover’s Sign: Detects involuntary leg movement when testing hip extension in a supine position.
Give-way Weakness: A sudden, inconsistent drop in strength when resisting a force from the examiner.
Tremor Entrapment Test: When a patient with an apparent tremor unconsciously entrains that tremor to a rhythmic external cue like tapping with the other hand.
Identifying such signs can be reassuring for both patient and clinician, demonstrating that the issue is functional rather than fabricated or “all in the head.” This approach reduces diagnostic uncertainty, helps structure treatment, and alleviates unnecessary invasive testing.
Overlapping and Comorbid Conditions
One of the biggest challenges in diagnosing FND is the wide overlap with other neurological or medical conditions. Patients with undiagnosed multiple sclerosis, for example, might initially present with symptoms that appear functional. Similarly, complex co-occurring conditions such as fibromyalgia, irritable bowel syndrome (IBS), or chronic fatigue syndrome (CFS) complicate the diagnostic picture. The presence of psychiatric comorbidities like anxiety or depression is common, but having these conditions does not negate the seriousness or authenticity of FND symptoms.
Management and Treatment Approaches
Given the multifaceted nature of FND, an integrated treatment plan that involves different specialists; neurologists, psychiatrists, psychologists, physiotherapists, and occupational therapists tends to be most effective. Treatment aims not only to reduce symptom severity but also to improve function, coping strategies, and overall quality of life.
Psychoeducation and Reassurance
Explaining the Diagnosis: Providing a clear explanation of FND, emphasising that symptoms are real even if no structural damage is present. Concrete visual aids (e.g., diagrams showing nervous system pathways) can help patients (and families) grasp how the brain can “misfire” and create functional symptoms.
Building Therapeutic Alliance: A compassionate and validating approach can help mitigate stigma and enhance treatment adherence. Patients often report relief in learning that FND is neither “imagined” nor a sign of irreversible organ damage.
Physical Therapy and Rehabilitation
Movement Retraining: Physical therapists familiar with FND use specialised techniques to encourage normal movement patterns, sometimes relying on distraction or automatic exercises (e.g., walking to a rhythm or with visual cues) that bypass maladaptive motor circuits.
Occupational Therapy: Focuses on real-world tasks like bathing, dressing, or cooking and helps patients relearn functional skills to regain independence.
Psychological Interventions
Cognitive Behavioural Therapy (CBT): CBT can be effective in reshaping unhelpful thoughts and beliefs that might sustain symptoms (e.g., catastrophising, hypervigilance to bodily sensations).
Trauma-Focused Therapy: If trauma or significant life stress underlies symptom onset, approaches like Eye Movement Desensitization and Reprocessing (EMDR) or prolonged exposure therapy can be beneficial.
Mindfulness and Relaxation Techniques: These may help reduce stress, anxiety, and symptom exacerbation.
Medication
While no medications specifically target FND’s root mechanism, pharmacotherapy can address comorbid depression, anxiety, or chronic pain. Selective serotonin reuptake inhibitors (SSRIs) and other psychotropic medications may improve overall well-being.
Multidisciplinary Approaches
Collaborative Care: A healthcare team that communicates regularly, ideally holding joint consultations can ensure that treatment strategies are aligned and consistent.
Support Groups: Peer support can reduce feelings of isolation, offer coping tips, and affirm that individuals are not alone in facing an often-misunderstood condition.
Prognosis
The prognosis of FND varies widely depending on individual factors such as symptom type, duration, presence of comorbidities, and access to specialised care. Research shows that a shorter duration of symptoms before diagnosis, early and consistent treatment, and the absence of severe psychiatric or psychosocial stressors may lead to better outcomes (Feinstein, 2011). Conversely, a prolonged delay in diagnosis or a care environment that invalidates the patient’s symptoms can deepen uncertainty, stigma, and chronic disability. In some cases, certain FND symptoms may persist long-term, but many individuals experience at least partial improvement, especially with appropriate, multifaceted intervention.
Crucially, emerging studies indicate that FND need not be viewed as a life-long, intractable disorder. Rehabilitation approaches that emphasise the brain’s neuroplastic potential, its ability to “retrain” itself offer hope for meaningful recovery. Engagement and perseverance in therapy, consistent follow-ups, and social support from family, friends, or community services remain key to maximising progress.
Simply Put
Functional Neurological Disorder (FND) exemplifies the intricate relationship between the mind, brain, and body. Far from a historical curiosity or mere “conversion” of emotional stress into physical symptoms, FND is a clinically significant condition driven by altered communication within neural networks. While it can be challenging to diagnose and treat, recent research and clinical practice developments have improved our understanding of how biological, psychological, and social factors intersect in FND. Recognising the legitimacy of these symptoms is crucial, as is providing patients with evidence-based treatments from movement retraining and psychological therapies to education and comprehensive care.
In many respects, the study of FND points to broader truths about health: that mind and body are inseparable, and that invisible or intangible factors like stress, past trauma, and subconscious processes can shape neurological function in profound ways. Through ongoing research into the mechanisms behind FND and through nurturing a patient-centred approach, clinicians and researchers continue to refine strategies for diagnosis, intervention, and recovery. As these efforts advance, individuals living with FND can benefit from a more empathetic healthcare environment, innovative therapeutic tools, and, ultimately, a greater likelihood of regaining control over their lives.
