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Somatisation / Functional Neurological Disorder

Updated: Sep 20, 2021



Somatisation: The term is often invoked to explain pain and suffering in patients


Lipowski - 'A tendency to experience and communicate somatic distress and symptoms unaccounted for by pathological findings, to attribute them to physical illness, and seek help for them'


Contestation - 'Labeling an experience as of unknown cause appears to begin the search for a cause rather than to end it'

 

Functional Neurological Disorder

Epidemiology

The second most common cause to see a neurologist - after headache

12 per 100,000 per year

Women > Men (3:1)

FND affects young to old (but uncommon under 10yo)

Costs to the health system are huge


Symptoms

High levels of disability (equiv to MS or epilepsy)

Co-morbid neurological conditions occur in 20% though!


Functional limb weakness/tremor/dystonia:

- Commonly unilateral. Sudden onset. Feel like the limb 'does not belong to them'

- Voluntary movements are often impaired bu automatic movements are preserved (mismatch)

- Weakness is often global involving flexors and extensors equally


Functional cognitive symptoms:

- Memory and concentration issues are common - but often an attentional deficit

- Up to 25% of patients presenting to memory clinics actually have functional cognitive disorders

- Cognitive testing in this group is inconsistent

- Evidence for how to treat this is lacking


Urinary retention and 'scan negative' cauda equina syndrome


Other

Speech difficulties, sensory symptoms, visual loss, diplopia, hearing loss or sensitivity, globus, persistent postural perceptual dizziness (PPPD) (chronic dizziness)


Pain and fatigue

These are very common in patients but FND itself does not encompass these presentations


Work up

Collect all presenting symptoms - particularly pathophysiological triggers (migraine, acue pain, panic, infection etc)

Non specific lifestyle symptoms such as: Fatigue, sleep, pain, and concentration


Diagnostic pitfalls

Failure to consider comorbidities other medical conditions


Misdiagnosis fear

Studies repeatedly show a low rate of misdiagnosis

Don't just diagnose it when clinical features are 'unusual'

Don't just diagnose it because you suspect they have stress/psychological comorbidities

Normal imaging - doesn't mean anything

Incidental MRI and EEG findings also does not mean pathology


Hoover's sign

Weakness of hip extension but returns to normal if you lift the other leg.


Functional tremor

These are often inconsistent/variable frequency

Ask the patient to use the better hand to copy a movement, and if the tremor stops in the other hand at the time then consider functional tremor

Can do the same with foot tapping, and tongue following hand movements

Tremors that move to another body part when that one is held still, is also functional


Functional dystonia

Often fixed abnormal posture whereas normal dystonia is usually mobile


Functional seizures

Paroxysmal events that often superficially resemble epileptic seizures or epilepsy

20% of patients have a comorbid diagnosis of dissociative seizures and epileptic


Signs of dissociative seizures include:

- Longer duration >90 secs, Fluctuating course, Asynchronous movements, side-to-side head or body movement, closed eyes, memory of the event


NB: Urinary incontinence and physical injury are poor discriminators

NB: Often confused with syncope and presents to cardiology (sudden closing eyes and falling to the ground)

NB: Improvement with treatment does not differentiate either - as 40% of dissociative seizures improve with medication

NB: Eye witness reports are unreliable


Pathophysiology of dissociative seizures

Similar to panic attacks in some settings - Brief prodrome of escalating severe symptoms with autonomic arousal. A seizure can be seen as an involuntary, learned, brain 'reflex' which gets rid of the sensations that are unpleasant but not always fearful

 

References:

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, 21(1), 28.

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