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Transient global amnesia
A paroxysmal, transient (less than 24 hours) loss of memory function.
Immediate recall ability is preserved, as is remote memory; however, patients
experience striking loss of memory for recent events and an impaired ability
to retain new information. In some cases, the degree of retrograde memory
loss is mild.
Causes
Temporary vascular insufficiency to hippocampus or its thalamic connections.
There are many theories as to how this can happen:
- A result of a migraine attacks: The most compelling evidence in
favor of the migraine theory is that patients who suffer from a TGA
event have a slightly higher incidence of a previous migraine.
- Seizure (eg, temporal lobe) is unlikely.
- A sequelae of transient ischemic attacks (TIA): as indicative
of cerebrovascular disease is unlikely.
- One theory proposed by Lewis is that venous congestion causes disrupted
blood flow to the thalamic or mesial temporal structures.
- The frequently cited triggers for TGA can increase either sympathetic
activity and/or intrathoracic pressure. This, in turn, could cause back-pressure
in the jugular venous system, disrupting intracranial arterial flow
with secondary venous congestion/ischemia to memory areas in the brain.
Symptoms
Mainly affects individuals >65yrs old. characterized by amnesia
in time, place and past memory but not to self for 3-12hrs (typically
less than 24 hrs). Many patients are anxious or agitated
- Neurologic examination of the patient typically fails to demonstrate
any abnormalities (other than memory dysfunction).
- If any lateralizing or focal findings are noted on the examination,
then the diagnosis of TGA should be questioned.
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Diagnosis
Lab Studies
- CBC with differential
- Electrolyte panel
- Screening clotting tests, including prothrombin time (PT), activated
partial thromboplastin time (aPTT), INR
- When a patient initially presents with TGA, stroke must be ruled
out.
Imaging Studies
Brain MRI and/or CT scan
- Any patient presenting with features of TGA should receive an imaging
test to rule out a stroke possibility, especially if significant risk
factors are present.
- MRI with DWI can readily demonstrate acute ischemic changes early
and guide management.
- If an MRI cannot be obtained readily, then at least a CT scan should
be done initially if the patient is presenting to an emergency department.
Other Tests
- ECG, EEG: These tests are important if the diagnosis of TGA is in
doubt. If symptoms have occurred more than once, then at least a routine
EEG should be done to help investigate a seizure possibility by demonstrating
any interictal activity.
Treatment
Medical Care: Once TGA is diagnosed, provide reassurance to the patient
and schedule at least one follow-up visit with a neurologist.
Diet: No dietary restrictions are necessary.
Activity: Avoid activities that could produce an unusual increase in
intrathoracic pressure (see trigger factors).
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