Herpes simplex encephalitis (HSE) is a rare neurological disorder characterized by inflammation of the brain (encephalitis). Common symptoms include headaches, fevers, drowsiness, hyperactivity, and/or general weakness. The disorder may have some symptoms similar to those associated with meningitis, such as a stiff neck, altered reflexes, confusion, and/or speech abnormalities. Skin lesions usually are not found in association with herpes simplex encephalitis. Herpes simplex encephalitis is caused by a virus known as herpes simplex virus (HSV).
Symptoms associated with herpes simplex encephalitis usually develop over several days, often without warning. Early symptoms include headaches, fevers, and seizures. Additional symptoms include drowsiness with general weakness (stupor), and confusion or disorientation.
After the initial symptoms appear, affected individuals may develop speech abnormalities such as a diminished ability to communicate by speech, writing, and/or signs (aphasia), absence of the sense of smell (anosmia), and memory loss. In some cases, behavioral changes such as hyperactivity or psychotic episodes occur. Some symptoms of herpes simplex encephalitis may mimic meningitis. These symptoms may include a stiff neck, altered reflexes, confusion, convulsions, and paralysis.
Individuals with herpes simplex encephalitis may develop more severe symptoms, including loss of consciousness, hallucinations, and partial paralysis (hemiparesis). In some rare cases, herpes simplex encephalitis may affect the nerve-rich membrane lining the eyes (retina), resulting in inflammation of the retina (retinitis).
Herpes simplex encephalitis is a complication of infection with the herpes simplex virus. In most cases, the disorder results from herpes simplex virus type I (HSV-I). In rare cases, usually in newborns (neonatals), the disorder is caused by herpes simplex virus type II (HSV-II).
Herpes simplex infection is an acute viral disease usually spread from person to person. It is marked by small fluid-filled blisters appearing on the lips or genitals often accompanied by fever. Herpes simplex encephalitis rarely occurs in conjunction with oral or genital lesions. The herpes virus may become immediately active or remain in the body in an inactive (dormant or latent) state. After being active, the virus may become inactive and then recur (reactivate).
Symptoms associated with herpes simplex encephalitis may occur due to tissue degeneration associated with bleeding (hemorrhagic necrosis) of a tongue-shaped lobe (i.e., temporal lobe) of the cerebral hemisphere.
Herpes simplex encephalitis usually occurs during early childhood or adulthood. It affects males and females in equal numbers. The disorder is the most common form of acute encephalitis in the United States with approximately 2,000 cases occurring per year. It accounts for 10 percent of all cases of encephalitis in the United States per year.
A diagnosis of idiopathic herpes simplex encephalitis is made based upon a detailed patient history, a thorough clinical evaluation, identification of classic symptoms, and a variety of specialized tests. These tests include polymerase chain reaction (PCR) in cerebrospinal fluid (CSF), which may confirm infection of CSF with the herpes simplex virus. In some cases, advanced imaging techniques such as computed tomography and magnetic resonance imaging (MRI) can also be beneficial in diagnosing a case of herpes simplex encephalitis.
Prompt treatment of individuals with herpes simplex encephalitis is important as it improves the efficiency of treatment options.
Treatment with the antiviral drug Zovirax (acyclovir) has resulted in a dramatic improvement of symptoms in most individuals with herpes simplex encephalitis. It is manufactured by GlaxoSmithKline.
Another antiviral drug that has been used to treat herpes simplex encephalitis is vidarabine. However, antiviral therapy may not benefit affected individuals in advanced stages of the infection. Antiviral therapy should be started as soon as herpes simplex encephalitis is suspected.
Seizures that are often associated with herpes simplex encephalitis may be treated with drugs that reduce, prevent, or suppress seizures (anticonvulsants).
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McJunkin JE, et al. La crosse encephalitis in children. N Engl J Med. 2001;11:801-807.
Maertzdorf J, et al. Herpes simplex virus type 1 (HSV-1) induced retinitis following herpes simplex encephalitis: indications for brain-to-eye transmission of HSV-1. Ann Neurol. 2000;48:936-39.
Sauerbrei A, et al. Virological diagnosis of herpes simplex encephalitis. J Clin Virol. 2000;17:31-36.
Garcia de Tena J, et al. The value of polymerase chain reaction in cerebrospinal fluid for the diagnosis of herpetic encephalitis: a report of 2 cases and a review of the literature. An Med Interna. 2000;17:81-83.
Chan PK, et al. Use of oral valaciclovir in a 12-year-old boy with herpes simplex encephalitis. Hong Kong Med J. 2000;6:119-21.
Garcia-Barragan N, et al. An unusual presentation of herpetic encephalitis. Rev Neurol. 2000;30:441-44.
Pavone P, et al. Early relapse of herpes simplex encephalitis. Clinical and therapeutic implications. Minerva Pediatr. 1999;51:395-98.
Ito Y, et al. Exacerbation of herpes simplex encephalitis after successful treatment with acyclovir. Clin Infect Dis. 1999;30:185-87.
Kaplan CP, et al. Cognitive outcome after emergent treatment of acute herpes simplex encephalitis with acyclovir. Brain Inj. 1999;13:935-41.
Levitz RE. Herpes simplex encephalitis: a review. Heart Lung. 1998;27:209-12.
McGrath N, et al. Herpes simplex encephalitis treated with acyclovir: diagnosis and long term outcome. J Neurol Neurosug Psychiatry. 1997;63:321-26.
Hokkanen L, et al. Cognitive recovery instead of decline after acute encephalitis: a prospective follow up study. J Neurol Neurosurg Psychiatry. 1997;63:222-27.
Paillard C, et al. Recurrence of herpes simplex encephalitis. Arch Pediatr. 1999;6:1081-85.
Foucher A, et al. Herpetic encephalitis: prognostic elements in adults and children (49 cases). Rev Electroencephalogr Neurophysiol Clin. 1985;15:185-93.
Taylor WB, et al. Ocular infection with herpes simplex virus type 1: prevention of acute herpetic encephalitis by systemic administration of virus-specific antibody. J Infect Dis. 1979;140:534-40.
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