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“Implantation Effect” Study Indicates Possible Reduction in Seizures for Epilepsy Patients

August 11, 2020

Although medications can control seizures in most patients with epilepsy, a third of epilepsy patients don’t respond to anti-seizure medication. For patients with “medication refractory epilepsy,” surgery to remove parts of the brain where seizures start may be their best bet at controlling their condition. But brain surgery is a significant and invasive procedure, and it’s not always possible to safely remove the seizure onset region without affecting important brain functions.

A recent study published in the journal Epilepsy and Behavior provides glimpses into another treatment option that does not involve removing parts of the brain. The retrospective review was conducted in the Yale Comprehensive Epilepsy Center, and included neurosurgeons Dr. Jason Gerrard, MD, PhD, Director of Stereotactic & Functional Neurosurgery at Yale School of Medicine, Dr. Dennis Spencer, MD, the director of Epilepsy Research at Yale School of Medicine and their colleagues at the Yale Department of Neurology, including Dr. Jennifer Percy, MD, the lead author, and Dr. Adithya Sivaraju, MD, the senior corresponding author. The researchers found that the diagnostic procedure before cutting in to the brain itself, can result in an immediate, although temporary, reduction in seizures in patients.

Before surgery to remove the seizure onset region in the brain, doctors start with an intracranial study, which uses an EEG from electrodes placed onto and within the brain to capture images of the brain during seizures to figure out where seizure activity starts. This intracranial study allows doctors to study the seizure activity and determine which parts of the brain they can remove safely.

The study looked at existing data from intracranial studies performed at Yale New Haven Hospital from 2002 to 2016 and showed that 36 percent of patients showed marked and long-term benefits from intracranial monitoring, even without surgical treatment, such as resection, ablation, or neurostimulation. They highlighted three patients who remained completely seizure-free for more than five years, two of whom had thalamic depth electrodes, said Gerrard, who has also studied the same phenomenon, termed ‘implantation effect’ in Parkinson’s patients.

Since the implantation effect is still poorly understood, it’s impossible to determine which medication refractory epilepsy patients might benefit from this positive outcome, nor how long the seizure reduction effect may last. But the new data supports the theory that a network of interconnected neurons can lead to seizures and disruptions in those networks can alter or improve seizure activity even without removing brain tissue.

Submitted by Jennifer Chen on August 11, 2020