The Relationship Between Epilepsy and Sleep

The Thomas Haydn Trust in an aid to understanding Epilepsy and Sleep has published this mobile article. This article is not extensive and should not be used as medical advice; it's intended for information purposes only. This dictionary is also available for download from www.thomashaydntrust.com/publications.htm in .pdf format. [Please note that this is version 1 and further updates may be availalbe]

Written by

M C Walker, S M Sisodiya

Institute of Neurology, University College London, National Hospital for Neurology and Neurosurgery, Queen Square, London, and National Society for Epilepsy, Chalfont St Peter, Bucks. London, and National Society for Epilepsy, Chalfont St Peter, Bucks. September 2005. This article can be reproduced for educational purposes.

Introduction

Epilepsy has a complex association with sleep. Certain seizures are more common during sleep, and may show prominent diurnal variation. Rarely, nocturnal seizures are the only manifestation of an epileptic disorder and these can be confused with a parasomnia. Conversely, certain sleep disorders are not uncommonly misdiagnosed as epilepsy. Lastly, sleep disorders can exacerbate epilepsy and epilepsy can exacerbate certain sleep disorders. This chapter is thus divided into four sections: normal sleep physiology and the relationship to seizures; the interaction of sleep disorders and epilepsy; and the importance of sleep disorders in diagnosis.

Normal sleep physiology and the relationship to seizures

Adults require on average 7 - 8 hours sleep a night. This sleep is divided into two distinct states - rapid eye movement (REM) sleep and non-REM sleep. These two sleep states cycle over approximately 90 minutes throughout the night with the REM periods becoming progressively longer as sleep continues. Thus there is a greater proportion of REM sleep late on in the sleep cycles. REM sleep accounts for about a quarter of sleep time. During REM sleep, dreams occur; hypotonia or atonia of major muscles prevents dream enactment. REM sleep is also associated with irregular breathing and increased variability in blood pressure and heart rate. Non-REM sleep is divided into four stages (stages I - IV) defined by specific EEG criteria. Stages I/II represent light sleep, while stages III/IV represent deep, slow-wave sleep.

Gowers noted that in some patients, epileptic seizures occurred mainly in sleep. Sleep influences cortical excitability and neuronal synchrony. Surveys have suggested that 10 - 45% of patients have seizures that occur predominantly or exclusively during sleep or occur with sleep deprivation. EEG activation in epilepsy commonly occurs during sleep, so that sleep recordings are much more likely to demonstrate epileptiform abnormalities. These are usually most frequent during non-REM sleep and often have a propensity to spread so that the epileptiform discharges are frequently observed over a wider field than is seen during the wake state. Sleep deprivation (especially in generalised epilepsies) can also 'activate' the EEG, but can induce seizures in some patients. Thus many units perform sleep EEGs with only moderate sleep deprivation (late night, early morning), avoidance of stimulants (e.g. caffeine-containing drinks) and EEG recording in the afternoon. Sleep-induced EEGs in which the patient is given a mild sedative (e.g. chloral hydrate) are also useful.

Sleep and generalised seizures

Thalamocortical rhythms are activated during non-REM sleep giving rise to sleep spindles. Since similar circuits are involved in the generation of spike-wave discharges in primary generalised epilepsy, it is perhaps not surprising that non-REM sleep often promotes spike-wave discharges. Epileptiform discharges and seizures in primary generalised epilepsies are both commonly promoted by sleep deprivation. Furthermore, primary generalised seizures often occur within a couple of hours of waking, whether from overnight sleep or daytime naps. This is most notable with juvenile myoclonic epilepsy in which both myoclonus and tonic-clonic seizures occur shortly after waking, and the