Vagus nerve stimulation (VNS) is a type of therapy that can be used to treat seizures. It is recommended only for patients whose seizures cannot be fully controlled with anticonvulsants, or anti-epileptic medications.
Seizures are common in Batten disease, an inherited neurodegenerative disorder that mostly commonly develops in childhood.
What is the vagus nerve?
The vagus nerve is the longest nerve in the body and has a branch running down each side of the body. It connects the brain to the neck, chest, and abdomen, transmitting nerve signals between the brain and different body parts including the heart, lungs, and digestive system.
Signals are passed along a nerve as an electrical impulse. This triggers a reaction at the synapse, or the end of a nerve, to release chemical messengers, called neurotransmitters, to stimulate or inhibit other nerves.
What is VNS?
VNS refers to any mechanism used to stimulate the vagus nerve, but most commonly involving surgically implanting a device that delivers electrical pulses to the brain, via the vagus nerve.
The device is similar to a heart pacemaker and is surgically placed under the skin, on the left side of the chest, under the collarbone. It’s connected to the left vagus nerve in the neck by a wire under the skin.
Seizures occur when the balance of nerve signaling in the brain is disrupted, resulting in an overstimulation as too many signals are fired. When the vagus nerve is stimulated, it can transmit signals to other parts of the brain and may stop or reduce the severity of a seizure, but it is not yet clear how exactly VNS is able to do this.
When is VNS used?
VNS may be used regularly to reduce, shorten, or prevent seizures, along with other medications. A few weeks following surgery, the device can be turned on and programmed by a healthcare professional to stimulate the vagus nerve at specific intervals and intensities. This can then be adjusted based on the patient and the number and severity of seizures.
VNS can also be used as a rescue treatment to quickly stop a seizure or reduce the recovery time. It can be activated to produce a stronger pulse for a short period of time by a magnet. If the patient shows warning signs of an oncoming seizure, the device can be activated by patients themselves, or by a parent or caregiver. It is essential that this is detailed in the patient’s emergency seizure management plan, and that relevant individuals are trained on when and how to use the VNS device.
Newer VNS models may automatically increase the impulses in response to an increase in heart rate, a common warning sign of an oncoming seizure.
VNS has been approved by the U.S. Food and Drug Administration since 1997 as an epilepsy therapy, and since June 2017, for children as young as 4 years old.
VNS does not work for all patients, and can have varying levels of effectiveness. In cases where the patient does not respond after two years, the device can be turned off or removed.
The device is powered by a battery that needs to be replaced periodically when it starts to get low, through a similar surgical procedure. The battery life will be reviewed as part of regular checkups.
As with any surgical procedure, there are small risks of complications associated with VNS implantation such as adverse reactions to the anesthetic, bleeding, or infection. Other side effects associated with VNS may include a sore throat, hoarse voice, coughing, or difficulty swallowing.
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