A systematic review was performed to provide evidence-based estimates about risk factors and incidence of SUDEP (Tellez-Zenteno, Ronquillo & Wiebe 2005). We searched Index Medicus, Medline, EMBASE, and the Cochrane database, for retrospective or prospective cohort and case-control English language studies exploring the risk factors and incidence of SUDEP in adults and children from 1966 to 2003. Of 83 potentially eligible articles 36 fulfilled eligibility criteria (29 cohort and 8 case-control studies). Salient findings follow:

Researchers do not use standard definitions of SUDEP. Standard definitions are essential for meaningful communication about clinical conditions. Some authors did not state a definition, some crafted their own, and others adhered to published definitions. A definition of SUDEP was explicit in 65% of studies, not clear in 29%, and not given in 6%. In many studies, the diagnosis of SUDEP was probable, not definite, because the most used definitions require post mortem data, and autopsies are performed infrequently in many settings. This suggests that the requirement of post mortem examination for a definitive SUDEP diagnosis may require revision. Specifically, how much certainty and precision does the post mortem examination add to the diagnosis of SUDEP?

The risk factors for SUDEP depend on the type of comparison. Studies exploring risk factors use one of two main comparison groups, i.e. non-SUDEP epilepsy deaths, and live people with epilepsy (PWE). Comparisons with non-SUDEP deaths explore best the circumstances surrounding death (e.g. seizures preceding death, place of death, AED levels at the time of death). Comparisons with live PWE explore best the lifestyle and clinical variables related to SUDEP (e.g. frequency of seizures, number of AEDs, use of other drugs). Therefore, the seemingly disparate risk factors found in these studies are really complementary.

High-risk and low-risk groups for SUDEP are identified. The risk of SUDEP is expressed as number of deaths per 1000 person-years. The risk is highest in studies of candidates for epilepsy surgery and epilepsy referral centres (2.2 to 10 per 1000), intermediate in studies including patients with mental retardation (3.4 to 3.6 per 1000), and lowest in children (0 to 0.2 per 1000). The incidence was similar in autopsy series (0.35 to 2.5 per 1000) and in studies of epilepsy patients in the general population (0 to 1.35 per 1000). PWE in the high-risk group typically suffer from more severe epilepsy, have frequent seizures, and require many AEDs. These factors are consistently associated with SUDEP (Langan & Nashef 2003; Lhatoo & Sander 2002; Stollberger & Finsterer 2004). The reasons for a lower risk in children require further investigation.

The contribution of SUDEP to overall mortality varies by risk group. As expected, in higher-risk groups SUDEP is a more frequent cause of death than in lower-risk groups. In studies of children, general population, epilepsy registers and autopsy series, SUDEP explained from 0 to 14% of deaths. In studies of epilepsy clinics, drug trials, epilepsy surgery or surgical candidates, and registers of patients with refractory epilepsy SUDEP explained from 29 to 75% of deaths.

Several aspects of SUDEP require further research. Prospective studies from seizure monitoring units could be fruitful. Standardisation of case ascertainment, definitions, and description of population sources is necessary to improve the analysis and interpretation of data. International panels could review the SUDEP definition and scientific journals could encourage researchers to adhere to standard definitions. Finally, researchers need to assess the impact that learning about SUDEP has on patients and their families, while exploring optimum risk communication and coping strategies for this infrequent, but devastating event.

Written By: Jose F. T