Last edited 08/2018

There is no single test which can diagnose epilepsy (1).  Investigations that can be helpful in epilepsy are:

  • EEG -
    • should be carried out only to support a diagnosis of epilepsy when the clinical history suggests that the seizure is likely to be epileptic in origin. The EEG should not be used in isolation to make a diagnosis of epilepsy.
  • CT and MRI- may be necessary in those suspected of having focal neurological deficit
    • neuroimaging should be used to identify structural abnormalities that cause certain epilepsies.
    • MRI should be the imaging investigation of choice in individuals with epilepsy. It is particularly important in patients
      • who develop epilepsy before the age of 2 years or in adulthood
      • who have any suggestion of a focal onset on history, examination or EEG (unless clear evidence of benign focal epilepsy)
      • in whom seizures continue in spite of first-line medication.
    • CT is used when MRI is not available or contraindicated to identify underlying gross pathology or for children and young people in whom a general anaesthetic or sedation would be required for MRI but not CT
    • neuroimaging should not be routinely requested when a diagnosis of idiopathic generalized epilepsy has been made.(1)
  • other investigation which should be considered to identify potential causes and/or to identify any significant co-morbidity include
    • in adults - appropriate blood tests (plasma electrolytes, glucose, calcium)
    • in children and young people - blood and urine biochemistry
    • measurement of serum prolactin is not recommended for the diagnosis of epilepsy
  • a 12-lead ECG
    • should be performed in adults with suspected epilepsy
    • should be considered in children in cases of diagnostic uncertainty


  • the suggested necessary investigations for a first seizure are (2):
    • clinical examination
    • assessment of seizure semiology
    • routine laboratory tests (depending on clinical circumstances)
    • cerebrospinal fluid (if encephalitis or subarachnoid haemorrhage is suspected and drug screening (depending on clinical circumstances)
    • early standard electroencephalography, if possible within 24 hours
    • sleep deprived electroencephalography within 1 week
    • high resolution magnetic resonance imaging, if possible