The EEG in nonepileptic seizures.

Nonepileptic seizures are episodes that resemble seizures but are not epileptic. The importance of EEG in the diagnosis of NES is that misread (overread) EEGs are an important contributor to the misdiagnosis of epilepsy. About 20% to 30% of patients with refractory "seizures" seen at epilepsy centers have been misdiagnosed, and the vast majority have psychogenic nonepileptic seizures (PNES). Many such patients have had previous EEGs interpreted as epileptiform. These misdiagnoses based on EEG are easily perpetuated, complicate management, and adversely affect outcome. The reasons for the overinterpretation of EEGs include the common misconception that phase reversals indicate abnormalities and not applying strict criteria to make sharp transients epileptiform. The diagnosis of PNES typically begins with a clinical suspicion and then is confirmed with EEG-video monitoring. However, ictal EEG may be negative in some partial seizures and may be uninterpretable because of artifacts. Movements can generate rhythmic artifacts that mimic an electrographic seizure. Analysis of the ictal semiology (i.e., video) is at least as important as the ictal EEG. Provocative techniques, activation procedures, or "inductions" can also be useful for the diagnosis of PNES.