Transient Global Amnesia

Basics

Transient global amnesia (TGA) has the following features:
- Episode of amnesia with abrupt onset
- No focal neurologic signs or symptoms
- Temporary, severe, anterograde amnesia:
  - Acute inability to form new memories
  - Permanent memory gap after the episode
- Temporary short-range retrograde amnesia:
  - More recent memories at more risk
  - Previously encoded memories unavailable only temporarily
- Gradually improves until only remaining memory deficit is the gap induced by the anterograde amnesia
  - Some retrograde loss may be permanent
- Mean duration of symptoms: 4–6 hr
  - Majority resolve within 8 hr
Incidence between 3 and 8 per 100,000 people:
- 75% occur in patients 50–70 yr old
- 10% occur in patients <50 yr
- Rare in patients <40 yr

Multimodal MRI, SPECT, and PET have shown some abnormalities of regional blood flow in selectively vulnerable hippocampal structures
The exact etiology of TGA is unknown; speculated causes are controversial:
- Vasoconstriction due to hyperventilation:
  - Psychogenic hyperventilation in setting of age-related cerebrovascular autoregulatory dysfunction
- Hippocampal venous congestion with Valsalva:
  - Increased prevalence of internal jugular vein insufficiency on ultrasound
  - Intracranial venous reflux not seen
- Migraine (in younger patients)
  - Destabilization of the CA1 sector of the hippocampus via glutamate release
  - Increased prevalence of migraine history in TGA patients
  - No increased frequency of TGA in patients with migraines
No correlation between TGA and thromboembolic cerebrovascular disease has been found
- TGA patients in fact have a lower risk of future cerebrovascular events than TIA patients

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