Severity of Stroke Predicts Epilepsy Onset

The more severe the stroke, the greater the likelihood of poststroke epilepsy (PSE). This was the finding of a Norwegian team of investigators who had previously confirmed that persons who have had a stroke are at risk for epileptic seizures.

Morten Lossius, MD, director of the Department for Education and Research at the National Centre for Epilepsy in Sandvika, and a team from the Norwegian Center for Health Services Research and Oslo University's Akershus University Hospital and Rikshopitalet took earlier research,¹ which evaluated short-term outcomes, a step further to evaluate the long-term prevalence of PSE, identify predictors, and assess whether patients who had received care in a stroke unit had better long-term outcomes than those who received care in a general medical ward. They found that the prevalence of PSE was 2.5% at 1-year follow-up after ischemic stroke, increasing to 3.1% at 7 to 8 years' follow-up.

Severity of the stroke was the key predictor of whether epileptic seizures would occur later, regardless of whether patients received specialized care in a stroke unit or recovered in a general medical ward. The researchers referred to the Scandinavian Stroke Scale to measure stroke severity. The study group consisted of 484 patients 60 years or older who presented to Akershus University Hospital within 24 hours of stroke onset between March 1994 and December 1995. The team found that those patients who, on hospital admission and day 1, had a Scandinavian Stroke Scale score of less than 30 were at higher risk for PSE.

NARROWING THE DEFINITION TO CLARIFY THE PREVALENCE

Stroke is the most common cause of epilepsy in persons older than 60 years, but prevalence rates of PSE vary according to the definition that a research team gives to PSE. Lossius' team used the definition found in the guidelines developed by the International League Against Epilepsy (ILAE),² which describe PSE as 2 or more unprovoked epileptic seizures occurring no earlier than 1 week after stroke. Thus, the team's findings on prevalence were in keeping with rates (average, 2.84%) reported in other published research founded on the ILAE definition. The team provides an overview of prevalence rates reported in the literature in their research article, which appears in the September issue of Epilepsia (Lossius MI, Rønning OM, Slapø GD, et al. Poststroke epilepsy: occurrence and predictors--a long-term prospective controlled study [Akershus Stroke Study]. Epilepsia. 2005;46:1246-1251).

CLINICAL IMPACT

Lossius and his team have stressed that additional studies focusing on prevention and management--for example, a look into whether acute thrombolysis can reduce the frequency of PSE--are needed. "PSE should be treated like any other symptomatic partial epilepsy. The patients are, however, usually old and more vulnerable to side effects. Therefore, one should be extra cautious when it comes to side effects and interactions with other drugs," Lossius added in a communication with Applied Neurology.

As for management of PSE in the United States, Edward B. Bromfield, MD, and Galen V. Henderson, MD, associate professor and assistant professor of neurology, respectively, in the Department of Neurology, Harvard Medical School,³ recommend careful analysis of whether an epileptiform seizure has occurred in a patient recovering from stroke. Differential diagnoses include syncope, migraine, transient ischemic attack, movement and sleep disorders, toxic metabolic disturbances, psychogenic nonepileptic seizures, and increased intracranial pressure.

The clinician must then consider whether the patient is at risk for a subsequent seizure; in this case, short-term treatment with an antiepileptic drug may be in order. Because most patients who have a late seizure (8 or more days after stroke) will have a subsequent one (meeting the criterion for a diagnosis of epilepsy), they should be considered for a longer term of therapy of 1 to 2 years. Those with confirmed PSE (2 late-stage seizures) should be treated for 2 years or longer. *

REFERENCES

1. Lossius MI, Rønning OM, Mowinckel P, Gjerstad L. Incidence and predictors for post-stroke epilepsy. A prospective controlled trial. The Akershus stroke study. Eur J Neurol. 2002;9:365-368.

2. Guidelines for epidemiologic studies on epilepsy. Commission on Epidemiology and Prognosis, International League Against Epilepsy. Epilepsia. 1993;23:592-596.

3. Bromfield EB, Henderson GV. Seizures and cerebrovascular disease. In: Ettinger AB, Devinsky O, eds. Managing Epilepsy and Co-existing Disorders. Boston: Butterworth-Heinemann; 2002:269-289.