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Functional neurological disorder matters because the symptoms are genuinely experienced and genuinely disabling, even though no disease process explains them and the patient is not producing them on purpose. It is diagnosed when neurological symptoms, such as weakness, seizures or sensory loss, are present but incompatible with any recognised neurological disease, and specific positive clinical signs confirm that incompatibility. For example, imagine a patient with apparent leg weakness that vanishes when they are distracted and asked to move the weak leg to keep their balance, a sign no organic nerve disease would produce. In practice, finding one of these positive signs, not just excluding disease, is what confirms the diagnosis.

Positive signs actively demonstrate the functional pattern rather than merely excluding disease. Hoover's sign shows involuntary hip extension in the weak leg when the patient flexes the opposite hip against resistance. Tremor entrainment shows the tremor's frequency shifting to match a rhythmic tapping task set by the examiner, something an organic tremor does not do. Take a patient with a resting tremor asked to tap along to a set rhythm: if the tremor's own rhythm shifts to match the tapping, that entrainment is a positive functional sign. In practice, these positive signs let clinicians make the diagnosis confidently, rather than simply telling the patient nothing was found.

• How useful is an apparent lack of concern about a severe deficit in diagnosing functional neurological disorder?
• How should functional neurological disorder be diagnosed?
• Which way of explaining functional neurological disorder to a patient best supports recovery?

• Somatic symptom disorder, excessive worry or distress about physical symptoms generally, unlike this disorder's specific positive neurological signs.
• Factitious disorder, symptoms consciously produced to occupy the sick role, rather than the unintentional symptoms of functional neurological disorder.
• Malingering, symptoms consciously produced for an external reward, whereas functional neurological disorder is not consciously produced.
• Hoover's sign, involuntary hip extension confirming a functional pattern, unlike the fixed findings of a genuine neurological lesion.

• ICD-11 does not list it as a criterion.
• A normal scan does not by itself establish the diagnosis.
• It is far too non-specific to confirm anything.
• Its absence is common in functional disorder, so it excludes nothing.
• No such site-specific usefulness is established.

• Extract the defining phenomenology, duration, severity and functional-impact clues.
• Match the pattern to the most specific diagnostic or assessment construct.
• Actively test the closest look-alike against the missing or contradictory clue.
• Choose the precise term rather than a broader category that is merely compatible.