Does SUDEP risk change over time?

Much of what we know about the frequency of sudden unexpected death in epilepsy (SUDEP) in the general epilepsy population comes from studies performed in the late 1990s and 2000s. The rate of SUDEP is estimated to be about 1 per 1,000 patients per year. Because SUDEP is relatively rare, to improve accuracy of estimates, some of these studies often examined deaths occurring over many years in a population with a known prevalence of epilepsy. Other studies looked only at deaths in a single year.

These approaches cannot tell us whether SUDEP risk is static – that is, a person with epilepsy will always have a 1 per 1,000 risk of SUDEP each year - or if it changes with the duration of illness.

Studies Show SUDEP Rate Decreases with Time

To examine changes in SUDEP rates over time, the incidence of sudden death needs to be looked at in large groups of people with epilepsy followed over many years. Two recent studies reported that, indeed, the rate of SUDEP decreases with time.

In the first study, Ryvlin and colleagues looked at a group of people or cohort of 40,443 patients with drug resistant epilepsy who had a vagus nerve stimulator (VNS). This information came from a device registry.

• A significant decrease in the SUDEP rate was seen 3-10 years after VNS implant compared to the first 2 years. The yearly incidence of SUDEP was lowered by about 32% in people who had VNS over the longer period of time.
• The authors speculated that lower SUDEP rates over time may have been due to the long-term effects of VNS. The lack of a control group without VNS makes it difficult to attribute this decrease to a specific treatment.

In the second study, Tomson and colleagues examined a population-based cohort of 60,952 patients in the Swedish National Patient Register. People in this group had an epilepsy diagnosis between 1998-2005 and were known to be alive in 2006. The authors looked at the rate of SUDEP over the following 6 years.

• The incidence of SUDEP was highest in the first year of follow up for this cohort and then declined by about 7% each year.

What do these studies mean?

Both studies show the risk of SUDEP declines over time among people with epilepsy. The reason for this decline is not yet clear. It may be due to

• Continued treatment of epilepsy through medication trials, surgery, or neurostimulation
• The tendency for the people at highest risk to die early from SUDEP
• Improved awareness of SUDEP risk in recent years

To better understand the reasons for lower SUDEP risks over time, more research is needed that follows the types of treatment and changes in seizure frequency. Understanding the factors driving the decline may help uncover effective ways to lower and ideally eliminate the risk of SUDEP.