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Should epilepsy patient have a vagal implant?

Q - A patient with severe intractable epilepsy has been offered a vagal nerve stimulator implant. What should I know about it?

A - Vagal nerve stimulator (VNS) implantation involves the placement of a stimulator device, a thin disc approximately 1.5 inches in diameter, deep under the skin in the upper left chest. This is connected to the left vagus nerve via a thin lead. It sends out an electrical signal at regular intervals, typically for 30 seconds every five minutes.

VNS implantation is indicated in intractable epilepsy which is unsuitable for resective neurosurgery. It appears to be effective both for generalised and partial epilepsies. There have been multiple excellent trials which indicate that while only about 2 per cent of patients show seizure freedom, some 40-50 per cent show seizure reduction of over 50 per cent and 70-80 per cent report significant improvement in quality of life over the one or two years after implantation. Efficacy of VNS implantation is similar to that of an effective new anti-epileptic drug.

Adverse effects are limited and rarely result in the need to switch off or remove the stimulator. Common effects include a slight pulling in the neck and hoarseness of voice for the period of stimulation. Surgery is a straightforward one-hour procedure.

Surgical complications occur in about 2 per cent; stimulus-associated adverse events are usually mild, transient and reversible.

VNS does not replace anticonvulsants but complements them.

Improvement in seizure control and quality of life often builds up over the first two years after implantation ­ this applies to all forms of refractory epilepsy. Typically, even if the seizure frequency is not significantly reduced, the seizure severity or the severity of post-ictal complications is much reduced.

Dr Jonathan Bird is consultant neuropsychiatrist, The Burden Centre for Neuropsychiatry, Frenchay Hospital, Bristol

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