Encephalitis Clinical Presentation

Updated: Aug 07, 2018
  • Author: David S Howes, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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The clinical presentation and course can be markedly variable. The acuity and severity of the presentation correlate with the prognosis. A history of mosquito or tick bites or exposure to mouse/rat droppings should be sought. Recognizing certain mammalian animal bite(s) associated with rabies or exposure to a bat in an enclosed space for which antirabies treatment was not obtained is very important.

The viral prodrome is typically several days and consists of fever, headache, nausea and vomiting, lethargy, and myalgias. The specific prodrome in encephalitis caused by varicella-zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), measles virus, or mumps virus includes rash, lymphadenopathy, hepatosplenomegaly, and parotid enlargement. Dysuria and pyuria are reported with St Louis encephalitis. Extreme lethargy has been noted with West Nile encephalitis (WNE).

The classic presentation is encephalopathy with diffuse or focal neurologic symptoms, including the following:

  • Behavioral and personality changes, with decreased level of consciousness

  • Neck pain, stiffness

  • Photophobia

  • Lethargy

  • Generalized or focal seizures (60% of children with CE)

  • Acute confusion or amnestic states

  • Flaccid paralysis (10% of patients with WNE)

Of note, severe headache is not always found. Less common is the complaint of paraspinal backache.

Symptoms of herpes simplex virus (HSV) infection in neonates (aged 1-45 d) may include localized skin, eye, or mouth lesions in the early phase of illness with encephalitis. Diminished alertness, irritability, seizures, and poor feeding develop later in the course of illness, and disseminated disease and shock are late findings.

Herpes simplex encephalitis (HSE) in older children and adults is not typically associated with active herpetic eruptions and is characterized by the acute onset of more severe symptoms of encephalitis early in the course of illness.

Toxoplasma encephalopathy accounts for as many as 40% of HIV-positive patients with neurologic disease who present with a subacute headache, findings of subtle to remarkable encephalopathy, and, often, focal neurological complaints/findings. Rarely, this may be the presenting symptom complex of profound immune suppression due to HIV infection.


Physical Examination

Look for supporting evidence of viral infection. The signs of encephalitis may be diffuse or focal. At the extremes, 80% of patients with HSE present with focal findings. Typical findings include the following:

  • Altered mental status

  • Personality changes are very common

  • Focal findings, such as hemiparesis, focal seizures, and autonomic dysfunction

  • Movement disorders (St Louis encephalitis, eastern equine encephalitis [EEE], western equine encephalitis [WEE])

  • Ataxia

  • Cranial nerve defects

  • Dysphagia, particularly in rabies

  • Meningismus (less common and less pronounced than in meningitis)

  • Unilateral sensorimotor dysfunction (postinfectious encephalomyelitis [PIE])

Findings of HSV infection in neonates (aged 1-45 d) may include the following:

  • Herpetic skin lesions over the presenting surface from birth or with breaks in the skin, such as those resulting from fetal scalp monitors

  • Keratoconjunctivitis

  • Oropharyngeal involvement, particularly buccal mucosa and tongue

  • Encephalitis symptoms, such as seizures, irritability, change in level of attentiveness, bulging fontanelles

  • Additional signs of disseminated, severe HSV include jaundice, hepatomegaly, and shock

As noted above, Toxoplasma infection causing encephalitis is found in immune-suppressed patients. They exhibit significant encephalopathy with lethargy or personality changes, and 75% present may present with focal neuropathology.



Encephalitis may be associated with a number of complications, including the following:

  • Seizures

  • Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)

  • Increased intracranial pressure (ICP)

  • Coma