What is transient global amnesia (TGA)?

Transient Global Amnesia: Clinical Features and Management

Transient global amnesia (TGA) is a benign, self-limiting neurological syndrome characterized by sudden onset of anterograde amnesia with preserved immediate recall and remote memories, typically lasting less than 24 hours, with complete resolution and no specific treatment required. 1

Clinical Features

TGA presents with distinctive characteristics:

• Core symptoms:

  • Sudden onset of anterograde amnesia (inability to form new memories)
  • Mild retrograde amnesia (difficulty recalling recent past events)
  • Preserved immediate recall and remote memories
  • Repetitive questioning about circumstances or location
  • Time disorientation and confusion 2

• Associated symptoms may include:

  • Vomiting, headache, blurry vision, dizziness, and nausea 2
  • No focal neurological deficits or altered consciousness 3

• Duration: Episodes resolve completely within 24 hours 1, 3

Diagnostic Criteria

The diagnosis of TGA is primarily clinical, based on the Hodge and Warlow criteria (1990) 3:

1. Episode must be witnessed and involve anterograde amnesia
2. No neurological signs or deficits
3. No features of epilepsy or active epilepsy
4. No recent head injury
5. Complete resolution within 24 hours

Precipitating Factors

TGA is often preceded by:

• Physical exertion
• Emotional stress
• Valsalva-like maneuvers
• Exposure to extreme temperatures
• High-altitude conditions
• Acute illness
• Sexual intercourse 2, 3

Pathophysiology

While not fully understood, TGA may be related to:

• Impaired venous drainage of the hippocampus 2
• Possible association with cerebral venous congestion or small thrombi in the deep cerebral venous system 4
• Potential relationship with migraine headaches 2

Diagnostic Evaluation

Although diagnosis is primarily clinical, investigations help exclude other conditions:

• Brain MRI: May show punctate areas of restricted diffusion in the hippocampi, though these findings can be subtle and may require specific timing (24-72 hours after onset) 5
• Basic laboratory tests: Complete blood count, electrolytes, glucose, thyroid function, and vitamin B12 levels to exclude metabolic causes 1
• EEG: To rule out seizure activity 6

Differential Diagnosis

TGA must be differentiated from:

• Stroke/transient ischemic attack
• Epileptic seizures
• Psychogenic amnesia
• Intoxication
• Metabolic disorders (hypoglycemia, hypoxia)
• Acute confusional states 1

Management

• No specific treatment is required during an episode 1, 2
• Reassurance to patient and family about the benign nature of the condition
• Observation until symptoms resolve
• No need for long-term medication 1

Prognosis

• Complete resolution within 24 hours
• Lifetime recurrence rate between 2.9% and 23.8% 1, 2
• No increased risk of subsequent stroke or TIA 1, 3
• Conflicting evidence regarding risk of future seizures or dementia 2

Clinical Pearls

• TGA is a diagnosis of exclusion 6
• Despite being called "transient," some mild cognitive impairment may persist beyond the acute episode 4
• TGA has also been associated with takotsubo cardiomyopathy in some cases 2
• Patients typically have no memory of events during the episode after recovery 5

TGA remains a fascinating clinical entity that, while alarming to patients and families, carries an excellent prognosis with complete recovery in virtually all cases.