SUDEP Rate Lower in Epilepsy Patients After VNS
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COPENHAGEN ― Results of a large long-term study suggest that patients with drug-resistant epilepsy treated with vagus nerve stimulation (VNS) have a reduced risk of sudden unexpected death in epilepsy (SUDEP).
"It appears reasonable to conclude that VNS treatment in the long term significantly reduces the risk of SUDEP," said Philippe Ryvlin, MD, PhD, Department of Clinical Neurosciences, CHUV, Lausanne, Switzerland.
A study by Annegers and colleaguessuggested that SUDEP decreased with adjunctive VNS therapy, but this was not confirmed in another comparable study by Granbichler and colleagues.
The current study increased the power of these previous two studies "by 100-fold," said Dr Ryvlin. The new findings were reported here at the 2nd Congress of the European Academy of Neurology.
Dr Ryvlin and colleagues used a US database for their study. As he explained to meeting delegates, the US Food and Drug Administration requires all patients with drug-resistant epilepsy receiving VNS to be registered in a database and then followed.
VNS Database
From the database, researchers identified patients implanted with VNS from 1988 to 2012. They calculated VNS exposure from the date of implant until death, device explant, known date the device was disabled, or last follow‐up date of December 31, 2012.
Because SUDEP has not yet been included as an International Classification of Diseases code for cause of death, researchers developed an algorithm to determine deaths probably related to SUDEP. They had information on contributing factors and, in almost half the cases, on circumstances of death from families, physicians, and autopsies.
The cause of 70% of deaths was considered not related to SUDEP, such as suicides, accidents, murders, or a neurological disorders such as stroke.
The other 30% of deaths were considered "potential" SUDEP. For example, when the cause of death was listed as epilepsy or convulsions, SUDEP might be "assumed" if the patient "was perfectly normal before and was found dead in bed in the morning," said Dr Ryvlin.
In the study that included 40,443 patients, there were 3689 deaths after a mean follow up of 6.9 years. According to their algorithm, the researchers concluded that 22% of these were related to SUDEP.
The SUDEP rate was 2.9/1000 patient-years (95% CI 2.8 - 3.1). This compared with a rate of 4.1 in the Annegers study and 3.3 in the Granbichler study.
The SUDEP rate for the first 1 to 2 years of VNS treatment was 3.6 (95% CI 3.8 - 4.0), and after 2 years it was 2.7 (95% CI 2.5 - 2.9).
“It's not a huge difference ― the odds ratio is 0.7 (95% CI 0.6 - 0.9) ― but it's significant; the confidence intervals do not overlap,” said Dr Ryvlin.