Errors in EEG interpretation and misdiagnosis of epilepsy. Which EEG patterns are overread?

The overinterpretation of EEGs is common and is an important contributor to the misdiagnosis of epilepsy. We reviewed our experience in order to clarify which EEG patterns are commonly overread as epileptiform.

We identified patients who were seen at our epilepsy clinic and were ultimately diagnosed as having conditions other than epilepsy. We selected those who had previously had an EEG read as showing epileptiform discharges and whose EEG was available for our own re-review.

37 patients met the above criteria. Eventual diagnoses were psychogenic nonepileptic seizures (10), syncope (7), other miscellaneous diagnoses (5) and unexplained nonspecific symptoms (15). None of the EEGs had epileptiform discharges. The descriptions of the abnormalities included 'temporal sharp waves' in 30, 'frontal sharp waves' in 2 and 'generalized spike-wave complexes' in 2. Three had no reports available to identify the alleged abnormality. The benign patterns mistaken for temporal (30) and frontal (2) sharp waves were simple fluctuations of background activity with temporal phase reversals.

By far the most common patterns overread as epileptiform are nonspecific fluctuations of background in the temporal regions, which are misread as temporal sharp waves.