Transient Global Amnesia
Definition and Causes:
The term transient global amnesia (TGA) refers to a complete memory loss for a short duration of time (often 1-8 hrs); lasting no more than 24 hrs. It is a well-known phenomenon whereby, individuals experience the sudden loss of memory for recent events and are unable to retain new information.
The precise cause of TGA is not known, however, some studies using brain imaging techniques suggest that there may be transient disruption in blood flow within key memory centers in the brain. Some have observed the association between TGA with:
- Physical or emotional stress
- Strenuous physical activity/exercise
There may be a small correlation between TGA and patients who suffer from migraines.
Many patients are anxious or agitated and may repeatedly ask questions concerning ongoing events.
- Sudden onset of memory loss for previous events (retrograde memory loss). The extent is variable from patient to patient. For some, the memory disturbance might be a few days, while others may have memory loss for months or even years
- The memory loss is often described as “confusion”, as it is not apparent to witnesses why the individual suddenly cannot recall specific events
- Personal identity and recognition of familiar objects or people are often retained, although the patient may not recognize recently acquired objects or people (e.g. newborn grandchild), if their association with the patient is within the period of retrograde memory loss
- Asks the same questions repeatedly because she or he does not remember the answer
- Is unable to recall the episode of memory loss once recovered
- Usually, there are no other symptoms, such as weakness, speech or vision problems
- When the symptoms begin to clear up, the patient’s memory is usually restored completely (sometimes within minutes). They continue to be amnestic for the event, or at best have an only sketchy memory of the event
Investigations and Treatment:
Physicians may enquire about:
- Unusual emotional or physical stress/strain
- Head trauma
- Prior history of seizures, migraine, stroke, and dementia
- Prescribed or illicit drug use
- Psychiatric history (depression, anxiety, bipolar)
- Recent infections (cold, flu)
- Potential exposure to infectious organisms (e.g. working environment and travel history)
- Vital signs: Blood pressure, heart rate, temperature, respirations
- Neurological examination: A brief assessment of memory plus evaluation of speech, vision, muscle tone, strength and reflexes, gait, posture, and balance
Diagnosis is largely based on
- Clinical presentation: Sudden loss of memory, in a fully conscious individual, that is transient and recovers fully
- Not associated with recent head trauma
- No history of seizures
- No abnormality of physical examination and labs (see below)
Labs and imaging:
Routine blood work, including electrolytes, white blood cell count, hemoglobin (to assess for anemia) as well as some blood work such as, a toxicology (drug) screen, and imaging of the brain by CT scan, MRI, and electroencephalogram (EEG) to assess for seizures may all be used to assess for or exclude other causes of memory disturbance.
TGA is usually a benign condition, and no specific treatment is required. Patients may be referred to a neurologist for an opinion. If TGA felt to be the most likely cause then patients are usually counseled and provided with some reassurance.
There is no medication required to treat TGA.
Risk Factors and Prevention:
The exact cause is unknown; so there is no standard prevention.
Overall prognosis is usually very good. While transient ischemic attacks (TIA) are a warning sign of an impending stroke, TGAs DO NOT herald a stroke. Generally, TGA is a solitary event; however, a small percentage (~5%) of patients who have had TGA may experience a recurrent event.
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