GPAtlas🧭 When to suspect
Transient global amnesia (TGA) is a striking but benign syndrome of sudden, isolated, profound anterograde amnesia – an abrupt inability to lay down new memories – in an otherwise well, fully conscious adult, usually aged over 50.
• The clinical hallmark is persistent, stereotyped, repetitive questioning ("What are we doing?", "Where am I?") asked in the same tone every few minutes.
• Personal identity, language and complex skills (making tea, driving, dressing) remain entirely intact.
• Episodes typically last 2–12 hours (mean around 6) and, by definition, resolve fully within 24 hours, leaving a permanent gap in memory for the event itself but no other deficit.
There is often a recognised precipitant:
• Vigorous physical exertion
• Emotional or psychological stress
• Immersion in cold or hot water
• A Valsalva manoeuvre
• Sexual intercourse
Two clinical skills matter most in primary care:
• TGA is a diagnosis of exclusion: during the acute episode it cannot be reliably distinguished from stroke, TIA, seizure or hypoglycaemia, so a patient who is still amnesic is a medical emergency.
• Once the diagnosis is secure, the news is reassuring – TGA is benign, needs no drug treatment, and does not increase the future risk of stroke, epilepsy or dementia.
| Diagnostic criterion (Hodges & Warlow) | Clinical note |
|---|---|
| Witnessed attack | A capable observer must be available – the diagnosis rests on the collateral history, as the patient cannot recall the event. |
| Clear anterograde amnesia | • Cannot retain new information for more than a few seconds during the attack • Mild retrograde amnesia may coexist |
| Preserved consciousness and identity | • No clouding of consciousness • The patient knows who they are and recognises family |
| Cognition limited to amnesia | No aphasia, apraxia or agnosia – attention, language and visuospatial skills are intact. |
| No focal or epileptic features | No limb weakness, sensory loss, visual field defect or seizure activity. |
| No recent head injury or active epilepsy | These point to alternative diagnoses (post-traumatic or epileptic amnesia). |
| Resolution within 24 hours | • Most settle within 2–12 hours • An episode lasting longer than 24 hours is not TGA |
TGA is not rare: incidence is around 3–8 per 100,000 per year, rising in those over 50, with a mean age of about 62 and a roughly equal sex distribution. The strongest recognised association is with a history of migraine.
Source: Practical Neurology · NEJM review
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