USMLE – Amnesia
Loss of memory for a period of time may be due to a transient toxic confusional state, a psychological fugue state, the postictal period after a seizure or the syndrome known as transient global amnesia. The latter two especially require careful distinction by analysis of the history. A period of amnesia often follows a seizure, either a complex partial or generalized seizure, and this may cause diagnostic confusion if the seizure was not witnessed-for example, if it occurred in sleep.
TRANSIENT GLOBAL AMNESIA
This is a syndrome affecting predominantly middle-aged patients in which there is an abrupt, discrete and reversible loss of short-term memory function for a period of some hours. During this time patients know who they are and can perform motor acts normally, but act in a bemused way, repeatedly asking the same questions. After 4-6 hours memory functions and behavior return to normal but the patient is left with a period of time for which he or she has complete amnesia. There are none of the phenomena associated with seizures and, unlike epileptic amnesia, transient global amnesia tends not to recur. There are no associated cerebrovascular risk factors, making a vascular etiology unlikely. Transient global amnesia is thought to be due to a benign process similar to that causing a migraine aura, occurring in the hippocampus. The patient has no physical signs and further investigation may not be needed if epilepsy can be excluded.