Makindo Medical Notes.com

TGA was first described in 1956 and since then epilepsy, transient ischaemic attacks (TIA), migraine and now intracranial venous stasis have been implicated in its aetiology but no firm aetiology has been proven and the prognosis appears to be benign

About

• Transient global amnesia was first described by Fisher and Adams in 1964 as a transient event in which there is altered behaviour with prominent memory loss
• Benign but poorly understood syndrome. Can be misdiagnosed as TIA

Aetiology

• Possibly migrainous but no headache
• Possible venous congestion with reduced perfusion of thalami or mesial temporal structures
• Poorly understood. Not a harbinger for stroke
• Rarely seen in those under 50

Clinical

• Diagnosis is historical and you need to talk with a witness
• Patient has a period of few hours of short-term memory loss
• Asks questions and confused about recent events
• Knows self, recognises family, familiar surroundings
• Often becomes distressed and agitated at the memory loss
• The amnestic period then comes to a gradual end and normality resumes
• the patient has no recall whatsoever of that time
• During the amnestic period the patient has no difficulty walking, talking, speaking
• There is no lateralising neurology. Social skills are normal.
• Precipitants include sex, exercise, exertion, swimming in cold water.
• Emotional event or indeed no obvious precipitant.

Diagnostic criteria [1]

• The attack was witnessed and reported.
• There was obvious anterograde amnesia during the attack.
• There was an absence of clouding of consciousness.
• There were no focal neurological signs or deficits during or after the attack.
• There were no features of epilepsy.
• The attack resolved within 24h.
• The patient did not have any recent head injury or active epilepsy.

Differentials

• TIA: NO ! no single arterial vessel occlusion does this precise pattern
• Temporal lobe epilepsy: the patient is obtunded, drowsy. rare de novo.
• Acute psychotic state: does not follow above requirements
• Functional/Stress

Investigations

• None needed if classical history. If the history is unclear or atypical and does not have the features discussed then needs a workup such as for TIA/Seizures.
• MRI: not needed but can show a usual tiny dot of DWI restriction in the hippocampus and associated areas not in keeping with typical infarction

Management

• None needed if classical history
• Reassurance. Avoid mislabels as TIA

References

• [1] Hodges JR, Warlow CP. Syndromes of transient amnesia: towards a classification. A study of 153 cases. J Neurol Neurosurg Psychiatry. 1990 Oct;53(10):834-43