Transient global amnesia involves the sudden loss of memory of recent events and a transient inability to retain new information. The incidence is higher in people 50 years of age and older, although it remains a rare occurrence. The patient with transient global amnesia may be disoriented, but behavior is otherwise normal. Most attacks resolve within several hours, although the patient remains amnestic to events that occurred during the episode. Brown conducted a literature review and presents criteria for emergency diagnosis of patients with transient global amnesia.
The following criteria should be used in the evaluation of a patient with transient global amnesia: an attack must be witnessed by an observer who can provide additional information; anterograde amnesia (inability to form new memories) must be present; no other cognitive impairment or loss of personal identity may be present; patients with transient global amnesia know their names and have had no recent history of head trauma or seizures in the past two years; focal neurologic signs and epileptic features are absent; and resolution of the attack should occur within 24 hours.
Most cases of transient global amnesia are preceded by an emotional stress, intense pain or cold, or strenuous physical activity. The specific cause is unknown. Patients may feel something is wrong but often have to be urged by a concerned observer to seek medical help. Most patients with transient global amnesia are disoriented to time and place and exhibit repetitive questioning that may last throughout the attack. Although patients are described as confused, they do not exhibit features of a true confusional state, can follow complex commands and do not confabulate.
When diagnostic criteria are properly applied, transient global amnesia is not difficult to diagnose because it is a unique entity. However, several disorders may be misdiagnosed as transient global amnesia. These include acute confusional states such as toxin-induced memory loss, psychogenic amnesia and transient complex partial seizures that present in the postictal state. Each of these, however, has distinct accompanying symptoms or physical findings.
Detailed work-ups are unproductive in patients who have all of the features of transient global amnesia unless other clinical indications are present. No evidence supports the use of toxicologic evaluations, metabolic and electrolyte testing, spinal tap with spinal fluid analysis, computed tomography of the head or electroencephalography unless the initial examination reveals an appropriate indication, such as focal neurologic deficits. If the diagnosis is in doubt, early neurologic consultation is appropriate. Family members and patients should be reassured that the attack will end within 24 hours. Patients whose attack has not yet ended should be closely followed.
There is no increased incidence of vascular deaths or epilepsy in patients with an episode of transient global amnesia, but a significantly greater proportion of persons with recurrent episodes of transient global amnesia go on to experience epilepsy than do control subjects. Patients with recurrent episodes might best be advised not to drive for 12 months. Stroke morbidity is not increased in patients with transient global amnesia, and the risk of a recurrent attack of transient global amnesia within five years ranges from 3 to 20 percent.
The authors conclude that transient global amnesia is a benign syndrome with a low risk of subsequent neurologic or vascular disease. Evaluations should be extensive only if focal neurologic signs accompany the presenting symptoms.