Encephalitis

Encephalitis is an inflammatory disorder of the brain. Common etiologies in immune competent individuals include herpes simplex virus (HSV), arboviruses, and a postviral syndrome mediated by the autoimmune system (30%). In immunocompromised patients, cytomegalovirus (CMV), toxoplasmosis, and fungal infections can cause encephalitis.

HSV causes 2000 cases of encephalitis annually in the United States, with no specific age-related, geographic, or seasonal preference. Mortality is 70% in untreated individuals, and patients with advanced disease almost always become permanently disabled. Herpes encephalitis can cause bizarre behavior that may be misdiagnosed as a psychiatric disorder.

Although the signs and symptoms discussed here pertain specifically to HSV encephalitis, most features are shared by the encephalitides caused by other entities.

Causes

Encephalitis is caused by any types of viral infections. Herpesvirus is the common cause and encephalitis can also result from infection following smallpox vaccination and reactivation of viral infection such as influenza, chickenpox, measles, mumps, and rabies.

Arthropod-borne viruses, which are usually transmitted by mosquitoes, cause arboviral encephalitis. People who live in warm, moist climates are at higher risk for this type.

Symptoms

• AMS +++++: personality changes ++++, drowsiness ++++
• Onset may be insidious or abrupt
• Headache +++
• History of an antecedent prodromal influenza-like illness +++
• Seizures +++: focal (85%), generalized (15%)

Signs

• Fever +++++
• Focal neurologic signs ++++, hemiparesis +++
• Of those conscious, difficulty speaking or complete aphasia +++
• Meningismus +++
• Evidence of increased intracranial pressure (papilledema or elevated opening pressure on LP) +++

Treatment

When encephalitis is caused by the herpes simplex virus or chickenpox, the condition can be treated with intravenous acyclovir, an antiviral drug. Because early treatment can reduce the chances of dying from encephalitis, it is very important to start treatment with acyclovir as soon as encephalitis is suspected, even if the exact cause of the illness is unknown. If encephalitis caused by the herpes simplex virus is treated promptly, the death rate of 70 to 80% drops to less than 30%.

Viruses carried by mosquitoes and ticks that cause encephalitis cannot be destroyed with drugs and will not respond to acyclovir. You can also use the symptoms with medications provided by the doctor to keep the patient comfortable.