What is transient global amnesia?

Transient Global Amnesia (TGA)

Transient global amnesia is a benign, temporary neurological syndrome characterized by sudden onset of anterograde amnesia with preserved immediate recall and remote memories, typically lasting less than 24 hours, with no established relationship to extracranial carotid or vertebral artery disease. 1, 2

Clinical Features

• Core characteristics:

  • Sudden onset of profound anterograde amnesia (inability to form new memories)
  • Mild retrograde amnesia (variable impairment of past memories)
  • Repetitive questioning about circumstances and events
  • Complete resolution within 24 hours
  • No other neurological deficits
  • Preserved immediate recall and remote memories

• Typical presentation:

  • Patients appear confused and disoriented to time
  • Repeatedly ask the same questions despite receiving answers
  • Often have time disorientation
  • May experience associated symptoms like vomiting, headache, blurry vision, dizziness, and nausea 2

Diagnostic Criteria (Hodges and Warlow)

1. Episode must be witnessed
2. Presence of anterograde amnesia during the attack
3. No clouding of consciousness or loss of personal identity
4. No focal neurological signs or deficits
5. No features of epilepsy
6. No history of active epilepsy or recent head injury
7. Resolution of symptoms within 24 hours 3

Common Precipitating Factors

• Physical exertion
• Emotional stress
• Valsalva-like maneuvers
• Exposure to extreme temperatures
• High-altitude conditions
• Acute illness
• Sexual intercourse 2

Pathophysiology

The exact mechanism remains unclear, but current theories include:

• Impaired venous drainage of the hippocampus
• Temporary dysfunction in the CA1 field of the hippocampal cornu ammonis
• Possible association with migraine mechanisms
• Not related to extracranial carotid or vertebral artery disease 1, 4

Diagnostic Approach

1. Clinical diagnosis based on characteristic presentation and exclusion of other causes
2. Neuroimaging:
   • MRI performed 24-96 hours after symptom onset may show punctate diffusion-weighted imaging lesions in the CA1 field of the hippocampus
   • CT scan to rule out acute pathology like stroke or hemorrhage
3. EEG to exclude seizure activity
4. Laboratory tests to exclude metabolic causes

Differential Diagnosis

• Transient ischemic attack (TIA)
• Transient epileptic amnesia (TEA)
• Complex partial seizures
• Psychogenic amnesia
• Acute confusional state
• Drug intoxication or withdrawal
• Migraine aura
• Early dementia 4, 5

Prognosis and Management

• Self-limited condition with complete resolution within 24 hours
• No specific treatment is required during an episode
• No increased risk of subsequent stroke or TIA 3, 2
• Recurrence rate: 2.9% to 23.8% over lifetime 2
• No need for long-term medication
• Reassurance to patients and families about the benign nature of the condition

Important Distinctions

• Unlike TIA, TGA is not associated with increased risk of future stroke 3
• Unlike seizures, TGA typically lasts hours rather than minutes
• Unlike psychogenic amnesia, TGA has a characteristic pattern of memory loss
• TGA is specifically mentioned in guidelines as not clearly attributable to extracranial carotid or vertebral artery disease 1

Clinical Pearls

• TGA is a diagnosis of exclusion 6
• The repetitive questioning pattern is highly characteristic
• Patients typically have no recollection of the episode after recovery
• TGA can occur after epilepsy surgery but should not be confused with seizure recurrence 5
• Despite memory impairment, patients can perform complex tasks during episodes

TGA represents a distinct clinical entity that, while dramatic in presentation, is benign in nature and outcome, requiring recognition primarily to avoid unnecessary interventions and provide appropriate reassurance.