Signs or symptoms of encephalitis (inflammation of the brain) can vary in scope, severity and duration. In most cases, symptoms do not tend to be serious. However, encephalitis can be fatal in some instances.

Symptoms of encephalitis can take anywhere from one to 30 days to appear, although most symptoms become apparent within five to 15 days after the initial infection. Some possible symptoms, which may range in severity and warrant medical attention, include the following:

• Drowsiness or lethargy (possibly extreme)
• Headache (possibly severe)
• Photophobia (aversion or sensitivity to light)
• Stiffness in the neck or back
• Fever
• Convulsions or vomiting
• Loss of balance
• Difficulty moving an arm or leg
• Difficulty walking
• Double vision
• Loss of consciousness
• Loss of sensation anywhere in the body
• Memory difficulties
• Problems with speech or hearing
• Seizures
• Sudden personality changes
• Bleeding within the brain (intracerebral hemorrhage)
• Paralysis
• Confusion
• Muscle weakness

Symptoms of encephalitis can be much more difficult to detect in infants. Infants younger than 3 months who have a fever higher than 100.4 degrees Fahrenheit (38 degrees Celsius) require immediate medical attention. Other symptoms typically associated with encephalitis in infants, include:

• Full or bulging “soft spot” (fontanel) on the head
• Body stiffness, or floppiness or decreased body tone
• Crying that is ongoing, or that worsens when picking up or touching the child
• Vomiting
• Lethargy
• Poor appetite

Encephalitis may occur along with inflammation of the membranes lining the brain (meningitis). When physicians are trying to diagnose meningitis, encephalitis or some overlap of the two, a distinguishing factor is often the patient’s brain function. Patients with meningitis might exhibit discomfort, lethargy or distraction by headache, but their cognitive function remains normal. However, individuals with encephalitis commonly exhibit aberrations in brain function, like speech or motion disorders, altered cerebral status or motor or sensory problems. Left untreated, encephalitis can lead to coma and death.