Brain biopsy is seldom performed but may be useful in patients with focal neurologic findings. It may be appropriate for patients with severe encephalopathy who show no clinical improvement if the diagnosis remains obscure. Rabies encephalitis and prion-related diseases (Creutzfeldt-Jakob disease and kuru) may be routinely diagnosed by culture or pathologic examination of brain biopsy tissue. Brain biopsy may be helpful to identify arbovirus and enterovirus infections, tuberculosis, fungal infections, and noninfectious illnesses, particularly primary central nervous system vasculopathies and malignancies.
With the exception of HSV, varicella-zoster virus, cytomegalovirus, and HIV, there is no specific therapy for viral encephalitis. Management is supportive and frequently requires intensive care unit admission to facilitate aggressive therapy for seizures, timely detection of electrolyte abnormalities, and, when necessary, airway monitoring and protection or reduction of increased intracranial pressure and maintenance of adequate cerebral perfusion pressure.
Intravenous acyclovir is the treatment of choice for HSV andvaricella-zoster virus infections. Cytomegalovirus infection is treated with ganciclovir. HIV infections may be treated with a combination of antiretroviral agents. M. pneumoniae infections may be treated with doxycycline, erythromycin, azithromycin, or clarithromycin, although the clinical value of treatingencephalitis associated with mycoplasmal disease is uncertain.
ADEM has been treated with high-dose intravenous corticosteroids, but it is unclear whether the improved outcome with corticosteroids reflects milder cases recognized by magnetic resonance imaging, fewer cases of ADEM caused by measles (which causes severe ADEM), or improved supportive care.
Among survivors, symptoms usually resolve over several days to 2 to 3 weeks. Although most patients with epidemic forms of infectious encephalitis (St. Louis, California, West Nile, and enterovirus infections) in the United States recover without sequelae, severe cases leading to death or substantial neurologic sequelae can occur with virtually any of these neurotropic viruses. About two thirds of patients recover fully before being discharged from the hospital. The remainder show clinically significant residua, including paresis or spasticity, cognitive impairment, weakness, ataxia, and recurrent seizures. Most patients with neurologic sequelae of infectious encephalitis at the time of hospital discharge gradually recover some or all of their function. The overall mortality for infectious encephalitis is approximately 5%.
Disease caused by HSV, Eastern equine encephalitis, or M. pneumoniae is associated with a worse prognosis. The prognosis may be worse for encephalitis in children younger than 1 year of age or with coma. Rabies, with very rare exceptions, is fatal.
Relapses of ADEM occur in 14%, usually within 1 year with the same or new clinical signs. Recurrences of ADEM may represent onset of multiple sclerosis in childhood.
The best prevention for arboviral encephalitis is to avoid mos-quito-borne or tick-borne exposures and to remove ticks carefully (see Chapter 122). There are no vaccines in use in the United States for the prevention of arboviral infection or for enteroviruses except for poliomyelitis. There are no specific preventive measures for HSV encephalitis except for cesarean section for mothers with active genital lesions (see Chapter 65). Rabies can be prevented by preexposure or postexposure vaccination. Influenza encephalitis can be prevented by use of influenza vaccination. Reye syndrome can be prevented by avoiding use of aspirin or aspirin-containing compounds for children with fever as well as use of varicella and influenza vaccines.