Functional Neurological Disorder

Original Editors - Abby Naville and Alex Piedmonte from Bellarmine University's Pathophysiology of Complex Patient Problems project.

Top Contributors - Alexandria Piedmonte, Jessica Hetzer, Abby Naville, Melissa Borst, Elaine Lonnemann, Rachael Lowe, Naomi O'Reilly, Simisola Ajeyalemi, Kim Jackson, Wendy Walker, Adam Vallely Farrell, Mason Trauger, 127.0.0.1, Evan Thomas, WikiSysop and Vidya Acharya

Definition/Description

Functional Neurological Disorder (FND) is a condition characterized by neurological symptoms that are genuine and disabling, but which arise from alterations in nervous system functioning rather than structural damage to the brain. The symptoms are inconsistent with known patterns of neurological disease and show variability within the same task and between different tasks.

This patient population is not intentionally simulating symptoms but is genuinely experiencing them. Symptom presentation may not follow typical anatomical patterns, such as dermatomal, myotomal, and sclerotomal distributions. Physical therapists should carefully document these patterns to recognise clinical signs of FND.

The DSM-5-TR refers to this condition as "functional neurological symptom disorder" with "conversion disorder" listed as an alternative term. Current understanding has moved away from requiring psychological causation, recognising that many patients do not have identifiable psychological stressors. Different presentations can be reported under the ICD-10-CM codes of F44.4, F44.6, and F44.7, depending on whether the symptoms are motor, sensory, or mixed.

Prevalence

Functional neurologic disorders affect approximately 50 per 100,000 individuals in community populations, with similar prevalence across all geographical regions. When compared to biological males, biological females are 60-75% more likely to be diagnosed. As consultation with neurology and psychiatry are vital for diagnosis, this difference may be due to social factors regarding psychiatric intervention, but may also reflect variation in symptom presentation; males are more likely to present with myoclonus or parkinsonism. Although FND affects individuals across the lifespan, it appears to peak in one's late 30s. FNDs present with the following incidences each year:

• All FND: 4 to 12 per 100,000
• Motor FND: 4 to 5 per 100,000
• Seizure type FND: 1.5 to 4.9 per 100,000

Characteristics/Clinical Presentation

The onset of FND symptoms can occur at any age, though often presents during adolescence or early adulthood. While symptoms may follow stressful life events, this is not always the case. Symptoms often appear neurological, encompassing sensory and/or motor presentations. Generally, patients present with one symptom at any given time and the severity of symptoms may vary under certain circumstances. Often symptoms will be present within an exam but are absent during functional movement or reflex reactions. The most common symptoms include:

General: • Variable symptom presentation • Symptoms inconsistent with known neurological patterns • Positive clinical signs on examination

Motor: • Impaired coordination or balance and/or gait disturbance • Weakness or paralysis • Tremor or abnormal movements • Speech difficulties • Swallowing difficulties

Sensory: • Altered touch or pain sensation • Visual changes • Hearing changes • Cognitive symptoms • Functional seizures • Normal structural neuroimaging • Positive functional signs on examination

Prognosis is variable but many patients can improve with appropriate treatment. Those with acute onset of symptoms may have better outcomes. Young children and adolescents tend to have better outcomes. A multidisciplinary approach involving neurology, psychiatry, and rehabilitation services provides the best outcomes.

Associated Co-morbidities

FND commonly co-occurs with other conditions. Research shows that patients with FND have similar rates of depression and anxiety to those with other neurological conditions like epilepsy or Parkinson's disease. Common comorbid conditions include:

• Depression
• Anxiety disorders
• Post-traumatic stress disorder
• Other functional disorders (irritable bowel syndrome, fibromyalgia, chronic fatigue)
• Chronic pain
• Dissociative disorders
• Other neurological conditions (FND can co-exist with conditions like epilepsy or multiple sclerosis)

Adverse life experiences and trauma are risk factors but are not present in all cases.

Diagnostic Tests

FND is diagnosed based on positive clinical signs rather than as a diagnosis of exclusion. The following criteria from the DSM-5-TR can be used:

Table 1. DSM-5-TR Diagnostic Criteria for Functional Neurological Symptom Disorder

A. One or more symptoms of altered voluntary motor or sensory function.

B. Clinical findings provide evidence of incompatibility between the symptom and recognised neurological or medical conditions.

C. The symptom or deficit is not better explained by another medical or mental disorder.

D. The symptom or deficit causes clinically significant distress or impairment in social, occupational, or other important areas of functioning or warrants medical evaluation.

Important note: The DSM-5-TR no longer requires identification of a psychological stressor or demonstration that symptoms are not intentionally produced.

Positive diagnostic signs include:

Hoover's sign: A test for functional leg weakness. The sign relies on the principle of synergistic contraction. When testing hip flexion of the affected leg, involuntary extension of the "weak" leg occurs when the unaffected leg is flexed against resistance.

Tremor entrainment: Functional tremor changes frequency or stops when the patient performs a rhythmic task with another body part.

Give-way weakness: Sudden loss of resistance during strength testing, unlike the smooth weakness seen in organic conditions.

Neuroimaging studies show altered brain network connectivity in FND, particularly in networks involved in self-agency and attention.

Etiology/Causes

The pathophysiology of FND involves alterations in brain network functioning rather than structural damage. Current models suggest:

• Altered functioning in brain networks that control voluntary movement and sensory processing
• Disruption in the sense of agency (feeling of control over one's movements)
• Abnormal predictive processing and attention
• Overactivity of the limbic system in some cases
• Dysfunction of brain networks that give movement the sense of voluntariness

While psychological factors and stress can be triggers, they are not required for diagnosis and are absent in many cases. Physical triggers such as injury, pain, or infection are equally important. The condition is best understood through a biopsychosocial model that considers multiple contributing factors.

Systemic Involvement

FND can affect multiple systems:

Motor:

• Weakness or paralysis
• Gait disturbance
• Tremor
• Dystonia
• Myoclonus

Sensory:

• Numbness
• Pain
• Visual symptoms
• Hearing changes

Cognitive:

• Memory difficulties
• Concentration problems
• Dissociative symptoms

Other:

• Functional seizures
• Speech difficulties
• Swallowing problems
• Bladder symptoms

Medical Management

Treatment requires a positive diagnosis based on clinical signs, with clear explanation to the patient that their symptoms are real and recognised. Treatment approaches include:

Education and Explanation

• Clear diagnosis based on positive signs
• Explanation that symptoms are real and potentially reversible
• Use of analogies (e.g., "software problem rather than hardware damage")

Physiotherapy

• Specialised physiotherapy focusing on retraining movement
• Different approach from standard neurological physiotherapy
• Focus on automatic movements and distraction

Psychological Therapy

• Cognitive behavioural therapy (CBT)
• Treatment of comorbid conditions
• Address maintaining factors

Multidisciplinary Approach

• Integration of neurology, psychiatry, psychology, and rehabilitation services
• Consistent messaging across team members

Medications

• No specific medications for FND
• Treatment of comorbid conditions (depression, anxiety, pain)

Physical Therapy Management

Physical therapy is a key treatment for motor FND. The approach differs from standard neurological physiotherapy:

Assessment:

• Thorough history including symptom onset and variability
• Identification of positive signs
• Assessment of movement patterns and compensatory strategies
• Functional assessment

Treatment Principles:

• Education about FND and positive prognosis
• Retraining normal movement patterns
• Using distraction and automatic movements
• Graded exposure to challenging activities
• Addressing unhelpful movement patterns

Specific Techniques:

• For weakness: Start with movements that work, progress gradually
• For gait disorders: Use external cues, backwards walking, dual tasks
• For tremor: Distraction techniques, changing movement patterns
• Focus on function rather than impairment

Behavioural Strategies:

• Positive reinforcement of normal movement
• Avoiding excessive focus on symptoms
• Building confidence in movement
• Addressing fear avoidance

Examples of Treatment Progression:

• Pre-gait activities: weight shifts, sit-to-stands, balance training
• Gait training with variations: different speeds, surfaces, dual tasks
• Functional activities relevant to patient goals
• Community reintegration

Evidence from randomised trials shows that specialised physiotherapy can be effective for functional motor disorders, with improvements in physical function and quality of life.

Differential Diagnosis

Conditions to Consider:

• Neurological conditions: Multiple sclerosis, myasthenia gravis, dystonia, epilepsy
• Rheumatological conditions: Systemic lupus erythematosus
• Metabolic conditions
• Structural lesions

Important Distinctions:

• FND can co-exist with other neurological conditions
• Diagnosis based on positive signs, not exclusion
• Presence of another condition does not exclude FND

Red Flags Requiring Further Investigation:

• Progressive symptoms following typical neurological patterns
• Objective signs of neurological disease
• Abnormal investigations consistent with symptoms

Resources

• Case Study: Functional Neurological Disorder Case Study
• Neurosymptoms.org - Patient Information
• Functional Neurological Disorder Society
• FND Action
• FND Hope International
• Physiotherapy for Functional Motor Disorders