Synopsis
Choose electroencephalography and peripheral neurophysiology for a defined clinical question, prepare patients safely and interpret sampled physiological data without treating normal or incidental findings as definitive diagnoses.
- EEG records cortical electrical potentials from scalp electrodes; it supports seizure classification, detects some electrographic seizures and evaluates encephalopathy, but it is not a brain scan and does not measure intelligence or thoughts.
- A normal routine EEG does not exclude epilepsy because interictal discharges are intermittent and deep or small generators may not reach the scalp. Epilepsy remains a clinical diagnosis supported by eyewitness history and appropriate tests.
- Incidental epileptiform or non-specific abnormalities do not prove that a collapse was epileptic. Interpret morphology, state, activation, medicines and pre-test probability with a clinical neurophysiologist.
Key red flags
Evolving rhythmic EEG activity in frequency, distribution or morphology can represent seizure, including without major motor signs. Critical-care patterns may lie on an ictal–interictal continuum and need urgent specialist interpretation.
Investigation priorities
Support epilepsy classification and identify focal or generalised cerebral dysfunction after a clinically assessed event.
Management branches
A transient event involving loss of awareness, abnormal movement, sensory phenomena or post-event change raises possible epilepsy.
- Obtain eyewitness and video evidence, examine, check ECG and provoking metabolic or structural factors and arrange urgent specialist assessment according to red flags and NICE timing.
- Request EEG only to support a clinically suspected epileptic event and classification; provide the event description, medicines and timing rather than asking the laboratory to 'exclude epilepsy'.