Imaging and Seizure Surgery Research Update – Dr. Hiro Otsubo

​Video electroencephalography, or vEEG, is a widely used technique in the assessment for epilepsy surgery. vEEG is used in a hospital setting in an epilepsy monitoring unit (EMU), where a medical team can observe the physical symptoms of a person’s seizure and match these symptoms with their brain activity. This helps surgeons to identify where in the brain the seizures are starting. The surgeon then determines whether this area can be surgically removed without affecting important brain functions (e.g., language and memory).

In order to gather accurate information, more than one seizure needs to be observed. For this reason, many patients are weaned off their anti-seizure drugs when they are admitted to the EMU. However, this does not mean that seizures will start immediately. It can take a while for the drugs to leave the system. Certain drugs stay in the system longer than others – for example, phenobarbital (PB) can take up to 5.8 days and zonisamide (ZNS) up to 2.9 days for levels to reduce in the blood by 50%. Dr. Hiro Otsubo and his colleagues wanted to investigate if these drugs could safely be stopped earlier, prior to admission to the EMU (known as the pre-admission session). Although stopping anti-seizure drugs can lead to more seizures and provide more information for the medical team, it can also increase the risk of adverse or harmful events. Adverse events can include clustered seizures, an increase in seizure severity, status epilepticus, or significant injuries.

The research team studied 87 adults and children with epilepsy who were taking two or more anti-seizure drugs. Participants were divided into two groups: those who were taking PHB or ZNS and those who were not. For both groups, anti-seizure drugs were gradually withdrawn in the 4-day pre-admission session and during the vEEG session until the first seizure occurred. The researchers then looked at how long it took from the start of withdrawal for the first seizure to occur.

Across both groups, only four patients experienced seizures in the pre-admission period. There were no adverse events during the pre-admission session. During the vEEG period, almost all remaining participants had seizures (22 of 23 people in the PB/ZNS group and 59 of 64 in the no PHB/ZNS group). However, the average time to the first seizure was much longer in the PB/ZNS group (6.1 days) compared to the no PB/ZNS group (2.8 days). During the vEEG session, several people experienced clustered or frequent seizures, and status epilepticus occurred in two participants.

In summary, the researchers suggest that for people taking PB or ZNS, stopping these drugs before admission to the EMU can help to ensure that enough seizures are observed during the limited time window of a vEEG monitoring session. Although no serious adverse events occurred during the vEEG session, the safety of early withdrawal may not apply to all types of epilepsy patients.

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