Abstract
In the investigation of psychogenic nonepileptic seizures (PNES), the main differential diagnoses are between convulsive PNES and tonic-clonic seizures, between swoon PNES and syncope, and between pseudoabsence PNES and absence seizures. For the best diagnostic certainty, events must be captured, ideally using video-electroencephalogram (EEG), including an electrocardiographic channel. The “video” part of video-EEG allows EEG changes (or lack of them) to be interpreted in the appropriate clinical context. When the diagnosis is based on less good data (e.g., video alone or EEG alone), then the limitations and constraints of the tests should borne in mind, and a lesser degree of certainty must be accepted. Tests such as serum prolactin (PRL) level and postictal EEG should be regarded as adjunctive rather than definitive. Excluding additional epilepsy with a good probability is not possible using investigations alone. In particular, one standard interictal EEG recording is of little value in excluding additional epilepsy, though multiple or prolonged recordings may offer additional sensitivity.