Transient global amnesia or transient epileptic amnesia?

Sir, We read with great interest the letter of McCorry and Crowley concerning an attack of transient global amnesia (TGA) considered secondary to herpes simplex viral encephalitis. Some features of the reported attack are unusual. The patient was a relatively young person: 39 years compared with an average age of 61 with TGA. At the beginning the patient suddenly became ‘distressed’; he realized the change and left office. With TGA, the disturbance is usually obvious to witnesses but not to the patient himself. The EEG performed on the second day exhibited right temporal sharp waves. During and after TGA, as a rule the EEG is normal. Epileptiform abnormalities do not occur. TGA has to be differentiated from epileptic seizures with prominent disturbances of mnestic functions. After the first description, a number of further patients have been reported under different designations: epileptic amnesic attack, pure amnesic seizure or transient epileptic amnesia (TEA). In most cases, the separation from TGA should be easy keeping in mind the frequent recurrence and short duration of TEA, the combination with further seizure types and the abnormal EEG findings including temporal sharp waves. Repetitively asking the same question is typical for TGA, but can also be observed with TEA. A long duration is unusual for TEA. However, pure prolonged transient amnesia can occur in the form of non-convulsive status epilepticus. We would suggest an epileptic aetiology for the attack reported by McCorry and Crowley, rather than TGA. The aetiology of TGA has been under discussion for years, advocating ischaemic, migrainous, epileptic and other causes. None of these appears completely convincing. Clearly symptomatic cases have been described with mild head injury, stroke and space-occupying lesions, among others. TGA symptomatic to herpes simplex encephalitis would represent a novelty. PCR results should be interpreted cautiously when neither signs and symptoms nor CSF findings or imaging results can readily be attributed to the virus detected. TEA marking the start of a temporal lobe epilepsy—non-lesional so far—seems to be a more plausible interpretation. The occurrence of some inconspicuous simple partial seizures (auras) in the past or further seizures in the future would clarify the situation and offer the opportunity of anti-epileptic drug treatment.