Viral encephalitis and epilepsy

Viral encephalitis presents with seizures not only in the acute stage but also increases the risk of late unprovoked seizures and epilepsy. Acute symptomatic and late unprovoked seizures in different viral encephalitides are reviewed here. Among the sporadic viral encephalitides, Herpes simplex encephalitis (HSE) is perhaps most frequently associated with epilepsy, which may often be severe. Seizures may be the presenting feature in 50% patients with HSE because of involvement of the highly epileptogenic frontotemporal cortex. The occurrence of seizures in HSE is associated with poor prognosis. In addition, chronic and relapsing forms of HSE have been described and these may be associated with antiepileptic drug-resistant seizures. Among the epidemic (usually due to flaviviruses) viral encephalitides, Japanese encephalitis (JE) is most common and is associated with acute symptomatic seizures, especially in children. The reported frequency of acute symptomatic seizures in JE is 7-46%. Encephalitis due to other flaviviruses such as equine, St. Louis, and West Nile viruses may also manifest with acute symptomatic seizures. In Nipah virus encephalitis, seizures are more common in relapsed and late-onset encephalitis in comparison to acute encephalitis (4% vs. 1.8%). Other viruses like measles, varicella, mumps, influenza, and entero-viruses may cause seizures depending on the area of brain involved. There is no comprehensive data regarding late unprovoked seizures in different viral encephalitides. Prospective studies are required to document the risk of late unprovoked seizures and epilepsy following viral encephalitis due to different viruses as well as to determine the clinical characteristics, course, and outcome of post-encephalitic epilepsy.