What is the prognosis of encephalitis?

Updated: Aug 07, 2018
  • Author: David S Howes, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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The prognosis is dependent on the virulence of the virus and the patient’s health status. Extremes of age (< 1 y or >55 y), immune-compromised status, and preexisting neurologic conditions are associated with poorer outcomes.

Untreated HSE has a mortality of 50-75%, and virtually all untreated or late-treatment survivors have long-term motor and mental disabilities. The mortality in treated HSE averages 20%, and the neurologic outcome correlates with the neurological disability present at the time of the first dose of acyclovir or comparable antiviral agents. Approximately 40% of survivors have minor-to-major learning disabilities, memory impairment, neuropsychiatric abnormalities, epilepsy, fine-motor-control deficits, and dysarthria.

Outcomes in arboviral JE and EEE are catastrophic, similar to untreated HSE, with high mortality and severe morbidity, including mental retardation, hemiplegia, and seizures. Other arboviruses cause substantially less morbidity and mortality. For example, St Louis encephalitis and WNE have a mortality rate of 2-20%, the higher rates found in patients older than 60 years. Long-term sequelae with St Louis encephalitis include behavioral disorders, memory loss, and seizures.

WEE is associated with few deaths and much less morbidity, although developmental delay, seizure disorder, and paralysis occasionally occur in children, and postencephalitic parkinsonism may occur in adults. CE is typically associated with mild illness, and most patients make a full recovery; however, the minority of patients with severe disease have a 25% chance of focal neurologic dysfunction. Death rates from WEE and LAC are less than 5%.

PIE secondary to measles is associated with a mortality rate approaching 40% of cases, with a high rate of neurologic sequelae in survivors. SSPE is uniformly fatal, although the disease course may last anywhere from several weeks to 10 years.

VZVE has a mortality of 15% in immune-competent patients and virtually 100% in immune-suppressed patients. The mortality for EBV encephalitis is 8%, with substantial morbidity found in approximately 12% of survivors.

Rabies encephalitis and acute disseminated encephalitis are virtually 100% fatal, although there are rare survivors reported in the medical literature.

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