Pure sleep epilepsy is traditionally defined as an “established pattern of seizures purely from sleep.” This retrospective and qualitative definition is difficult to apply in clinical practice and to use when developing guidelines for important daily activities such as driving. Patients who have had a first-ever unprovoked seizure from sleep often have questions about their risk for seizure recurrence, particularly from wakefulness, and driving implications. Therefore, there is a clinical need to determine the risk for seizure recurrence in this population, including developing an evidence-based definition of pure sleep epilepsy.
For a study published in Neurology, my colleagues and I assessed the rate of seizure recurrence from sleep and wakefulness after a first ever seizure from sleep, and a more specific definition of pure sleep epilepsy was proposed. Consecutive adult patients after a first-ever unprovoked seizure from sleep were recruited over 11 years. After baseline seizure workup, patients were prospectively followed to determine seizure recurrence from sleep and wakefulness and outcomes were correlated with potential clinical predictors of awake seizures.
Risk of Awake Seizure After a Sleep Seizure
Of the 239 patients with a first-ever seizure from sleep, 174 (73%) had seizure recurrence. Most patients had their second (75%) and third (81%) consecutive seizures from sleep. In addition, 89 patients (37%) developed awake seizures, with half occurring within 2 years of the initial seizure. The probability of an awake seizure within 1 year of a first-ever seizure from sleep was 13.9%, falling to 2.0% to 5.3% per year after 3 years (Figure). Additionally, the risk for awake seizures after three or more consecutive seizures from sleep was 8.7% within the first year of the third seizure, with the annual risk falling to below 5% in subsequent years.
Predictors for awake seizures after a first-ever sleep seizure on multivariate analysis were a positive family history of epilepsy (P=0.01) and EEG epileptiform abnormalities, particularly generalized epileptiform abnormalities (P=0.03). However, neither were sufficiently discriminative to have significant clinical implications.
Defining Pure Sleep Epilepsy: Implications for Clinical Practice and Driving
The key take-home point from this study is that most patients have seizure recurrence after a first unprovoked seizure from sleep, with many continuing to have sleep-only seizures (ie, pure sleep epilepsy). However, approximately one-third of patients with a first-ever seizure from sleep develop awake seizures, with half of these occurring as their second-ever seizure. For the majority of the others who eventually had an awake seizure, this occurred within 3 years of the initial seizure. Therefore, pure sleep epilepsy can be defined as three consecutive seizures from sleep or 3 consecutive years of sleep-only seizures with no previous awake seizures. This definition allows clinicians to prospectively diagnose pure sleep epilepsy with greater confidence.
These findings have implications for driving. Many jurisdictions around the world permit patients with pure sleep epilepsy to drive a private motor vehicle, with the stipulated period of seizures only during sleep ranging from 1-3 years. As no patient with epilepsy is ever truly free of the risk for future awake seizures, driving authorities and the community at large accept a certain risk of seizure-related accidents to allow patients to return to the road. A relative risk of a crash of less than or equal to two, equating to an annual awake seizure risk of less than 20%, is commonly deemed acceptable in driving guidelines, which is equivalent to driving when sleep-deprived or within legal alcohol limits. Based on this relative risk, the results of our study provide support for allowing patients to return to driving a private motor vehicle after 12 months of sleep-only seizures with no previous awake seizures. These findings may inform driving decisions and allow driving authorities to develop evidence-based driving guidelines for patients with pure sleep epilepsy.