Investigations

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

Notes:

• 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

References:

1. Rogers G. Introduction to Epilepsy. Chapter 127 - The role of primary care in the management of epilepsy. Published online by Cambridge University Press 2012
2. NICE. Epilepsies in children, young people and adults. NICE guideline NG217 Published April 2022