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

Reference:

• (1) Epilepsy Action 2005. The role of primary care in epilepsy management 2.
• (2) National Clinical Guideline Centre (NCGC) 2012. The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care.