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Electroencephalography (EEG) investigation


Electroencephalography (EEG) continues to provide valuable insight into brain function by demonstrating focal or diffuse background abnormalities and epileptiform abnormalities. It is an extremely valuable test in patients suspected of epilepsy and in patients with altered mental status and coma. Patterns in the EEG make it possible to clarify the seizure type; it is indispensable for the diagnosis of nonconvulsive status epilepticus and for separating epileptic from other paroxysmal (nonepileptic) episodes.

There are EEG patterns predictive of the cause of the encephalopathy (i.e., triphasic waves in metabolic encephalopathy) or the location of the lesion (i.e., focal polymorphic delta activity in lesions of the subcortical white matter).

Routine EEG

A routine EEG takes about 1 hour. It takes about 30 minutes to set up the recording and another 30 minutes for the recording itself. Some EEGs such as sleep deprived or Neonatal Intensive Care Unit recordings do take longer.

One of the common reasons for having the test is when epilepsy is suspected or to help decide what type of epilepsy a patient has. In some patients who have had a seizure an EEG will help predict whether they are likely to have more. In difficult cases we may need record the EEG for longer periods of time using sleep deprived, melatonin or ambulatory EEG recordings.

Neonatal EEG is performed if a neonate is suspected of having epileptic seizures. In neonates, epileptic seizures are often characterised clinically by subtle motor behaviour such as elevation of a limb, eye deviation, eyelid flutter, tonic posturing, bicycling movements of the legs, apnoea, and so on. The EEG is indispensable in establishing the epileptic nature of the motor activity by demonstrating an associated ictal pattern.

Go to the Neurophysiology overview page.

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