EEG in epilepsy

Last reviewed 01/2018

NICE have stated the role of EEG in making a diagnosis of epilepsy

• an EEG is done only to support a diagnosis of epilepsy in patient in whom the clinical history suggests that the seizure is likely to be epileptic in origin
• the standard EEG can help classify individuals with a clinical diagnosis of an epileptic seizure into different epilepsy seizure types and epilepsy syndromes
• if an EEG is considered necessary, it should be performed after the second epileptic seizure but may, in certain circumstances, as evaluated by the specialist, be considered after a first epileptic seizure"
• an EEG should not be
  • used to exclude a diagnosis of epilepsy in a patient in whom the clinical presentation supports a diagnosis of a non-epileptic event
  • performed in the case of probable syncope because of the possibility of a false positive result
  • used in isolation to make a diagnosis of epilepsy
• repeated standard EEGs may be helpful when the diagnosis of the epilepsy or the syndrome is unclear. However, if the diagnosis has been established, repeat EEGs are not likely to be helpful
• when a standard EEG has not contributed to diagnosis or classification, a sleep EEG should be performed
  • repeated standard EEGs should not be used in preference to sleep or sleep-deprived EEGs
• long-term video or ambulatory EEG may be used in the assessment of children, young people and adults who present diagnostic difficulties after clinical assessment and standard EEG
• photic stimulation and hyperventilation should remain part of standard EEG assessment The patient and family and/or carer should be made aware that such activation procedures may induce a seizure and they have a right to refuse (1)

This contrasts with advice from a BMJ review that states essential diagnostic procedures in patients with a first seizure include (2):

• early standard electroencephalography, if possible within 24 hours
• sleep deprived electroencephalography within 1 week

An abnormal EEG pattern seen in children, young people and adults presenting with a first unprovoked seizure can be used to predict seizure recurrence (1)

Reference:

• (1) National Clinical Guideline Centre (NCGC) 2012. The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care.