Mean LOS: 8.2 days
Description: MEDICAL: Nervous System Infection, Except Viral Meningitis
Encephalitis, or inflammation of the brain, usually occurs when the cerebral hemispheres, brainstem, or cerebellum is infected by a microorganism. Approximately 2000 cases of encephalitis are reported each year in the United States, but this is probably only a fraction of the cases. Most forms have mortality rates of less than 10%, with the exception of eastern equine encephalitis, where mortality is as high as 50%. Determining the true incidence is impossible because reporting policies are neither standardized nor rigorously enforced.
Encephalitis has two forms: primary and postinfectious (or parainfectious). The primary form of the disease occurs when a virus invades and replicates within the brain. Postinfectious encephalitis describes brain inflammation that develops in combination with other viral illnesses or following the administration of vaccines such as measles, mumps, and rubella. In that case, encephalitis occurs because of a hypersensitivity reaction that leads to demyelination of nerves.
When the brain becomes inflamed, lymphocytes infiltrate brain tissue and the meninges of the brain. Cerebral edema results, and ultimately, brain cells can degenerate, thus leading to widespread nerve cell destruction. Complications from encephalitis can be short term or lifelong. Bronchial pneumonia and respiratory tract infections may complicate the course of encephalitis. Patients may go into a coma and experience all the complications of immobility, such as contractures and pressure ulcers. Other complications include epilepsy, parkinsonism, behavioral and personality changes, and mental retardation. A comatose state may last for days, weeks, or months after the acute infectious state.
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