Epilepsy and viral infections.

In Clinical Science Viral infections may cause seizures via several pathogenetic mechanisms. Systemic infections, such as influenza, can lead to metabolic compromise, as well as occasional direct central nervous system (CNS) invasion—even though not usually neu-rotrophic. Although viral infection confined to the meninges rarely causes seizures and does not increase risk for later epilepsy , encephalitis is a major cause of seizures and subsequent epilepsy (1). In addition to the acute pathogens, syndromes caused by " unconventional " agents, such as Creutzfelt–Jacob disease or progressive multifocal leukoencephalopathy, often are associated with seizures or myoclonus at some time in their course. Seizures are caused by direct CNS infection by human immune deficiency virus (HIV), as well as with the secondary infections associated with acquired immune deficiency syndrome (AIDS). In addition, recent data suggest that persistent infection with a latent agent, human herpesvirus 6, may be associated with development of mesial temporal sclerosis. Systemic Viral Infections and Seizures Several systemic infections may involve the CNS. Neurologic complications of influenza—although rare in comparison to the overall incidence of the disease—include seizures provoked by fever and systemic illness, encephalitis, extrapyra-midal syndromes, Guillain-Barré syndrome, transverse myelitis, myositis, and myocarditis (2). Although neurologic complications are reported most often in children, this may be related to higher overall attack rates; adults over 60 were relatively spared, perhaps due to prior exposure to antigenically similar agents. Influenza may be associated with as many as 20% of uncomplicated febrile seizures (3). Some viral strains may be more likely to cause neurologic disease. H1N1 patients had more severe neurological disease, including encephalopathy and focal findings, but the incidence of seizures was the same as in previous influenza epidemics. Children with neurological complications during the 2009 H1N1 epidemic were more likely to have had underlying neurological disease—such as seizures or developmental de-lay—than those with neurologic involvement during previous seasonal influenza (4). In patients with influenza and altered mental status, evidence for direct CNS infection is limited but may include edema and increased thalamic signal on MRI (5). Seizures occur in about 50% of patients. Most patients recover without sequelae, and there are no data to suggest that antiviral treatment affects the neurologic course (2). A rarer influenza-associated acute encephalopathy/ encephalitis (> 80% occurring in children) can present with a fulminant neurological illness in association with any influenza viral serotype and may be associated with an underlying genetic disorder in proinflammatory cytokine …