Errors in EEG Interpretation and Misdiagnosis of Epilepsy

Abstract

Background/Aims: 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. Methods: 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. Results: 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. Conclusions: 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.

The tragedy of over-read EEGs and wrong diagnoses of epilepsy

“…Approximately 30% of patients seen at epilepsy centers for refractory seizures do not have seizures and have been misdiagnosed [1]. As illustrated here, many of them have histories not in the least suggestive of seizures, and have their diagnosis based largely (and sometimes solely) on an 'abnormal' EEG [2][3][4][5][6][7][8].…”

“…to order an EEG than to take a history. The combination of vague, nonspecific symptoms with an equivocal (weak) EEG abnormality is a common cause of inappropriate diagnoses of seizures [4][5][6][7][8]10].…”

“…The EEG patterns that can be over-read include well-known normal variants, but in reality these are relatively rare and the vast majority of over-read patterns are either wicket rhythms or 'nameless variants', that is, simple fluctuations of sharply contoured background rhythms or fragmented a activity that do not fit into a well-described EEG waveform [6,8]. These 'nameless' fluctuations of normal backgrounds have been described under different names and are found on most EEGs [11][12][13][14][15][16].…”

“…These 'nameless' fluctuations of normal backgrounds have been described under different names and are found on most EEGs [11][12][13][14][15][16]. Differentiating normal variants from meaningful spikes and sharp waves can at times be challenging, but helpful rules have been described [6][7][8][17][18][19][20][21][22][23][24]. Unfortunately, this is only well known by EEG-epilepsy specialists, and most EEGs are read by general neurologists (just like most ECGs are initially read by noncardiologists).…”

Clinical Significance of Epileptiform Activity in Electroencephalogram

“…При определении эпилептиформной активно-сти следует помнить о другой, очень важной стороне вопроса -неправильной интерпретации различных электрических потенциалов на ЭЭГ и их толковании как эпилептиформной активности [26,59]. Это могут быть доброкачественные ЭЭГ-варианты в бодрство-вании (например, лямбда-волны, полифазные по-тенциалы, гипервентиляционная гиперсинхрония), во сне (например, гипнагогическая гиперсинхрони-зация, маленькие острые пики, вертекс-потенциалы) (рис.…”