Encephalitis

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Diagnosis

Diagnosis of encephalitis is based on the following:

• Medical history (including recent exposure to insects, travel, personality changes, and contact with unusual animals or illnesses)
• Neurological examination
• Blood and urine tests
• Imaging tests (e.g., CT scan, MRI scan, EEG)
• Spinal tap

A neurological exam is performed to evaluate mental status, detect neurological problems such as motor dysfunction and seizures, and help determine which area of the brain is affected.

Blood and urine tests are used to isolate and identify viruses. Enzyme-linked immunosorbent assays (ELISA), including IgM-capture ELISA (MAC-ELISA) and IgG ELISA, can identify viruses that cause encephalitis soon after infection. Polymerase chain reaction (PCR) can identify small amounts of viral DNA.

Computed tomography (CT scan) and magnetic resonance imaging (MRI scan) produce computer images of the brain and are used to detect abnormalities such as swelling (edema) and bleeding (hemorrhage). MRI is able to detect abnormalities earlier in the course of the infection.

Electroencephalogram (EEG) involves placing electrodes on the scalp to record and analyze electrical activity in the brain. Wave patterns can suggest seizure disorder or a specific viral infection, such as herpesvirus.

Spinal tap, or lumbar puncture, is performed to detect signs of infection in cerebrospinal fluid and help make a diagnosis. In this procedure, a needle is inserted between two lower spine (lumbar) vertebrae, cerebrospinal fluid is collected, and the fluid is analyzed for elevated white blood cell counts, blood, and the presence of virus.

Treatment

Treatment for encephalitis depends on the cause. Some cases of viral encephalitis can be treated successfully if medication is started as soon as possible.

If herpes simplex encephalitis is suspected, antiviral medication such as acyclovir (Zovirax®) or ribavirin (Virazole®) is often administered immediately to improve chances for recovery and prevent complications. Side effects of these medications include nausea, vomiting, and headache. Treatment for viral encephalitis also includes palliative care.

There is no cure for arboviral encephalitis and the goal of treatment is to relieve symptoms (palliative). Palliative care may include intravenous fluids (to prevent dehydration), antibiotics (to prevent secondary infections), and other medications (to prevent complications). Diuretics (e.g., furosemide, mannitol) may be administered to reduce intracranial pressure and benzodiazepines (e.g., lorazepam [Ativan®]) may be administered to prevent seizures.

Prognosis

Prognosis depends on the type of encephalitis, the patient's age, overall health, and status of the immune system. Encephalitis caused by rabies, eastern equine encephalitis, Japanese encephalitis, and untreated viral encephalitis caused by herpesvirus carry a high risk for serious neurological damage and death. The prognosis is worse in very young patients, elderly patients, and patients with compromised immune systems.

Acute disseminated encephalitis and encephalitis caused by rabies infection is often fatal. Rabies is transmitted through the bite of an infected animal and there is no cure once symptoms have developed.

Prevention

In areas where arboviral encephalitis is prevalent, insecticide spraying may be used to control outbreaks. Wearing insect repellent and avoiding outdoor activities when mosquitoes are active may also be helpful.

A vaccine for Japanese encephalitis is available in the United States. People traveling to areas of the world where this disease is prevalent should be vaccinated. A vaccine for tick-borne encephalitis is available in Europe.

Administering antiviral medication (e.g., acyclovir) as soon as possible when encephalitis caused by herpes virus is suspected may prevent serious neurological complications.

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