Transient global amnesia and the forgotten EEG pattern

We read with interest the excellent retrospective study of YooSeok Kwon, reporting a high proportion (22.9%) of patients with transient global amnesia (TGA) and epileptiform discharges (mostly with a left dominance) detected within days of the episode of TGA. Authors should be commended for having conducted a study aimed to shed further light on the pathogenesis of such a fascinating disorder. It is noteworthy to consider that epileptiform discharges on the EEG are not by themselves synonymous with epilepsy. Previous reports in the literature described in EEG recordings of these patients a frequent occurrence of Subclinical Rhythmic Electrographic Discharges of Adults (SREDA), an otherwise uncommon distinctive rhythmic pattern seen on EEG in subjects older than 50 years, considered to be unrelated to epilepsy. Surprisingly, this rare EEG pattern, which has a prevalence of 1 per 2500 recording, has been reported to occur much more frequently (3–25%) among TGA patients. The correlation of SREDA with mechanisms which produce TGA is debatable, although – overall considered – it seems unlikely. However, the risk of considering this spiky pattern fortuitously found in EEG of patients with TGA as truly epileptic, with following misdiagnosis of transient epileptic amnesia should be taken into account and avoided. This and other EEG patterns of uncertain significance that occur without any correlation with epilepsy should be well known by neurologists and promptly recognized to avoid misdiagnosis of epilepsy due to an overinterpretation of normal sharp patterns.