2 Neuroscience2.11 Integrated neurobiology of syndromes and states
2.11.12 Medically unexplained symptoms
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Written by Resident Doctor Committee · Published
Terminology
Functional neurological disorder (FND) is diagnosed from positive clinical features in symptoms such as weakness, tremor or dissociative seizures, with no structural lesion explaining them.
"Medically unexplained" describes uncertainty, not a mechanism, and can wrongly suggest the symptoms are unreal.
ICD-11 bodily distress disorder depends on symptoms and the person's responses to them, not on whether the symptoms are medically explained.
Real symptoms, not deception
Functional symptoms are experienced as involuntary.
Inconsistency or normal imaging does not establish deception. Factitious disorder and malingering need separate evidence.
FND can coexist with epilepsy, stroke or multiple sclerosis.
Positive signs
FND is diagnosed from a coherent pattern of positive signs. Normal investigations alone are not enough, and no scan confirms or excludes it.
Sign | What it shows |
|---|---|
Hoover's sign | Weak voluntary hip extension on one side returns to normal strength when the opposite hip is flexed against resistance |
Tremor entrainment | Tremor shifts towards the rhythm tapped by another limb |
Distractibility | Symptoms change when attention shifts |
Hoover's sign separates functional from structural leg weakness, because it shows that automatic hip extension is preserved.
A gap between automatic and voluntary movement does not mean the person produces the symptom deliberately.
Causes and recovery
Trauma is neither required nor sufficient for FND, so clinicians should not search for a hidden psychological precipitant.
Physical illness, injury, surgery, pain or panic can precipitate symptoms.
Symptoms can improve, sometimes quickly, with explanation, rehabilitation and psychological support. Rapid change does not show prior conscious control.