What is the workup for transient global amnesia?

Workup for Transient Global Amnesia

The workup for transient global amnesia (TGA) is primarily clinical, with neuroimaging (MRI) performed 24-96 hours after symptom onset to confirm the diagnosis by identifying characteristic punctate lesions in the hippocampus. 1, 2

Clinical Diagnosis

TGA is characterized by:

• Sudden onset of anterograde amnesia with preserved immediate recall and remote memories
• Repetitive questioning about current events
• Preservation of other cognitive functions
• Self-limited episodes lasting less than 24 hours
• No other neurological deficits

Diagnostic Criteria (Hodge and Warlow)

• Episode must be witnessed
• Anterograde amnesia must be present
• No neurological signs or deficits
• No features of epilepsy or active epilepsy
• No recent head injury
• Resolution within 24 hours 3

Diagnostic Workup

History

• Document duration and pattern of memory loss
• Identify potential triggers:
  • Physical exertion
  • Valsalva-like maneuvers
  • Emotional stress
  • Sexual intercourse
  • Exposure to extreme temperatures
  • High-altitude conditions 4

Physical and Neurological Examination

• Complete neurological examination to rule out focal deficits
• Cognitive assessment focusing on:
  • Short-term memory
  • Orientation
  • Other cognitive domains (which should be intact) 1

Neuroimaging

• MRI of the brain: Optimally performed 24-96 hours after symptom onset
  • Look for punctate lesions in the CA1 field of the hippocampal cornu ammonis
  • Present in approximately 50% of cases with standard 1.5-3T MRI
  • Detectable in up to 90% of cases using 7T MRI 5, 2
• CT scan: May be performed initially to rule out other acute conditions but is not sensitive for TGA-specific findings 1

Laboratory Tests

• Basic laboratory tests to exclude metabolic causes:
  • Complete blood count
  • Electrolytes
  • Glucose
  • Thyroid function
  • Vitamin B12 levels 6

Differential Diagnosis

The workup should exclude other causes of acute amnesia:

• Stroke or TIA (especially involving posterior circulation)
• Seizures (complex partial seizures)
• Toxic-metabolic encephalopathy
• Wernicke's encephalopathy
• Psychogenic amnesia
• Early dementia 1, 4

Important Considerations

• TGA is a benign condition with no increased risk of subsequent stroke or TIA 1
• No specific treatment is required during an episode
• Recurrence rate is estimated between 2.9% to 23.8% over a lifetime 4
• The diagnosis is primarily clinical, but MRI can help confirm it
• Patients and families should be reassured about the benign nature of the condition 5

When to Consider Additional Testing

• If symptoms persist beyond 24 hours
• If there are any focal neurological deficits
• If there is a history of head trauma
• If there are features suggestive of seizures
• If the clinical presentation is atypical 3

By following this structured approach to the workup of TGA, clinicians can accurately diagnose this benign condition while appropriately ruling out more serious causes of acute amnesia.