Investigations
History and Physical Examination
In order to diagnose epilepsy, it is important that your physician take a detailed history that will focus on the description of the seizure and pertinent information surrounding the seizures. These details will help distinguish seizures from other events such as syncope (fainting) or a movement disorder (such as tics), among other events. The physician will also take a thorough medical and neurological history that will assist in determining risk factors for epilepsy.
The physical examination is an important part of the assessment and is used to provide clues to what is causing the seizures and where in the brain the seizures may be coming from.
Investigations
There are different kinds of investigations that help diagnose epilepsy and potentially identify a cause for the seizures. The most common initial investigations are electroencephalography (EEG) and neuroimaging with MRI. Occasionally genetic testing may be indicated.
Electroencephalography (EEG)
EEG is the most informative investigation in those with epileptic seizures. The EEG uses electrodes that are precisely placed onto the scalp to record brain activity, typically for 30-40 minutes. The information is displayed on a monitor and is interpreted by an expert (neurophysiologist) trained in reading EEGs. There are procedures where people are asked to follow in order to enhance the information that can be obtained from the EEG such as sleep deprivation the previous night, sleeping during the EEG, hyperventilation (rapid breathing), and photic stimulation (flashing lights). Most EEGs have simultaneous video recording. This helps to identify clinical signs (behaviours) that occur with seizures.
The EEG is very useful in the diagnosis of epilepsy, the type of epilepsy (focal or generalized), where the seizures may be coming from, and possibly the epilepsy syndrome. Since it can only record the brain activity from the scalp, it is possible that it may not record seizures in individuals where their seizure focus is deep in the brain. In contrast, some individuals may have an abnormal EEG but not have epileptic seizures. Therefore, physicians must interpret EEG results carefully and also use the rest of the available person’s history. Most people who read EEGs have had rigorous training and passed the Canadian Society for Clinical Neurophysiology’s EEG exam .
Neuroimaging
Neuroimaging is an important investigation in patients with epilepsy, especially as part of the workup for epilepsy surgery. This is discussed in more detail elsewhere on this website.
Genetic/Inborn errors of metabolism
In recent years, a number of genetic disorders that may cause epilepsy have been identified (for example Dravet’s syndrome) and genetic disorders which may be associated with epilepsy (for example Tuberous Sclerosis and Trisomy 21). Thus genetic testing is playing an increasingly important role in finding the cause of an individual’s epilepsy and may impact their treatment. Genetic testing is usually performed by taking a blood test.
Inborn errors of metabolism are conditions people may be born with that may be associated with seizures. Individuals with these disorders will usually present with epilepsy during infancy and childhood with additional symptoms such as developmental delay. Inborn errors of metabolism are disorders where there is a block in a metabolic pathway leading to an abnormal buildup or a deficiency of products which may lead to seizures. An example of an inborn error of metabolism which may present with seizures is pyridoxine deficiency or Glucose Transporter 1 Deficiency. These may be tested for by specific blood, urine, cerebrospinal fluid tests as well as genetic testing.
If seizures become difficult to treat, or the diagnosis is unclear, additional investigations may be performed and can include the following:
Ambulatory EEG
This is a type of mobile EEG that is powered by a battery pack and allows continuous EEG recording for 24-72 hours. The electrodes are placed on the scalp in the hospital but the individual is able to walk around and sleep at home. Most ambulatory EEG monitoring systems do not have video although this is increasingly becoming available as an option. This type of EEG is useful because it increases the likelihood of capturing a seizure event.
Video-EEG Monitoring/Epilepsy Monitoring Unit
This procedure occurs in-hospital with prolonged concurrent video and EEG monitoring which may last 24 hours to many days. Anti-seizure medications may be withdrawn under a physician’s care in order to increase the likelihood of recording a seizure. It is of particular use for determining whether an event is a seizure or not, clarifying seizure type or for localizing a seizure focus for epilepsy surgery candidates.
Neuropsychology
A neuropsychological assessment is a series of behavioural and cognitive tests that examine different aspects of thinking, learning, and behavior in order to assist with finding a seizure focus. They also help to determine the effects of seizures on the brain. A neuropsychologist is a type of psychologist who administers the test and specializes in evaluating cognition and brain function. This may be performed before and after surgery. Neuropsychological tests may also be used to determine an individual’s educational and workplace needs.
Invasive EEG Monitoring
This very specialized video-EEG monitoring is often used prior to epilepsy surgery and involves recording seizures using electrodes that are surgically implanted directly on the brain (beneath the skull) or in the brain (depth electrodes). It is typically used when there is insufficient information from scalp EEG recordings regarding the exact location of the epilepsy focus.