SUDEP: definitions and classifications
[Part 1: Facts; Nashef L]
SUDEP is a category of deaths in people with epilepsy, and not a condition. It is likely that this category includes cases with different mechanisms and circumstances. Definitions for what is included in this category are needed as they allow for comparisons between different studies and for monitoring trends.
Two SUDEP definitions/classification systems (Annegers, 1997; Nashef, 1997) have been in use for more than 15 years. The Nashef definition (Sudden, unexpected, witnessed or unwitnessed, non traumatic and non drowning death in an individual with epilepsy, with or without evidence for a seizure and excluding documented status epilepticus, where post-mortem examination does not reveal a toxicologic or anatomic cause for death) focused on strictly defined cases with negative post-mortem, while the Annegers definition additionally gave guidance on classifying the many cases where information is incomplete, with 'definite' (negative post-mortem), 'probable' (sudden death as above, in benign circumstances but without post-mortem) and 'possible' categories. Both definitions have been useful. The strictly defined category may be particularly helpful in studying mechanisms, while broader categories need to be taken into account in epidemiological work, especially in population based work where information is often lacking.
These complementary definitions together have provided the basis for classification of SUDEP cases in most studies to date. They have been more recently combined in one classification system (Nashef et al., 2013). The aim was to extend, clarify and unify definitions in use while maintaining consistency with most published research in the last two decades. The combined classification, in addition to concepts inherent in the previous definitions, includes nine main recommendations:
The use of the term ‘unexpected’ rather than ‘unexplained’;
That the category of SUDEP be applied irrespective of whether there is evidence of a terminal seizure;
The ‘possible’ SUDEP category should be used only for cases with competing causes of death, with cases left unclassified when data are insufficient to reasonably permit their classification;
Cases that would otherwise fulfil the definition of SUDEP should be designated as SUDEP ‘plus’ when evidence indicates that a pre-existing condition, known before or after autopsy, could have contributed to the death, which otherwise is classified as SUDEP (e.g., coronary insufficiency with no evidence of myocardial infarction or long-QT syndrome with no documented primary ventricular arrhythmia leading to death);
To be considered SUDEP, the death should have occurred within 1 hour from the onset of a known terminal event;
For status epilepticus as an exclusion criterion for SUDEP, the duration of seizure activity should be 30 minutes or more;
A specific category of SUDEP due to asphyxia should not be designated, the distinction being largely impractical on circumstantial or autopsy evidence, with more than one mechanism likely to be contributory in many cases;
Death occurring in water but without circumstantial or autopsy evidence of submersion should be classified as ‘possible’ SUDEP. If any evidence of submersion is present, the death should not be classified as SUDEP;
A category of ‘near’ SUDEP should be agreed to include cases in which cardiorespiratory arrest was reversed by resuscitation efforts with subsequent survival for more than 1 hour.
The proposal also included scenarios that demonstrated each SUDEP category and recommended that if disagreement existed about which category fits a particular case, a consensus decision is reached by a panel of informed reviewers to adjudicate the classification of the case.
Classification systems are by their nature to some extent arbitrary, particularly in a situation where most deaths are unwitnessed and where there is no pathological diagnosis of SUDEP. Nevertheless, the older definitions have been workable and stood the test of time, and the unified definition will hopefully fit in with the older classifications and be applicable and useful in different studies and for monitoring purposes. It is likely that additional clarification will be needed in time. Already the category of 'fatal near SUDEP' has been applied in cases of 'near' SUDEP where the death occurred more than one hour after the terminal event (Ryvlin et al., 2013).
Consultant Neurologist and Reader
King's College Hospital, London, UK
How to cite:
Nashef L. SUDEP: definitions and classifications. In: Hanna J, Panelli R, Jeffs T, Chapman D, editors. Continuing the global conversation [online]. SUDEP Action, SUDEP Aware & Epilepsy Australia; 2014 [retrieved day/month/year]. Available from: www.sudepglobalconversation.com.