ENCEPHALITISENCEPHALITIS

Overview

Encephalitis is acute inflammation of the brain. It often coexists with inflammation of the covering of the brain and spinal cord (meningitis).

Encephalitis is more common in children and young adult.

Encephalitis ranges from mild to severe and may result in permanent neurological damage and death.

Causes and Risk Factors

Encephalitis is most common caused by a viral infection. Many types of viruses may cause it.

Exposure to viruses can occur through :

- Breathing in respiratory droplets from an infected patient.

- Contaminated food or drink.

- Insect, especially mosquito bites.

- Skin contact.

Types

Primary Encephalitis

This type results from viral infection of the brain and spinal cord. Primary encephalitis may occur in isolated cases (sporadic) or occur in many people at the same time in the same area (epidemic). The most common type of sporadic infection

is herpes simplex encephalitis, which is caused by the herpes virus.

Arthropod-borne viruses (transmitted through the bite of insects and ticks) may cause arboviral encephalitis. Mosquitoes are the most common agents of transmission.St Louis encephalitis.

Japanese encephalitis.

Enterovirus : Coxsackie virus, Echovirus, PoliovirusRabiesCytomegalovirusEpstein-Barr virus

Secondary Encephalitis This type develops as a complication of a viral infection or reactivation of a latent virus. Viruses can become reactive when the immune system is suppressed by other conditions (e.g., malnutrition, stress, disease). Infections that may cause secondary encephalitis include influenza, chickenpox (varicella-zoster), measles (rubeola), mumps, and German measles (rubella).

Secondary encephalitis that develops as a result of a variola virus infection following smallpox vaccination or reactivation of another viral infection (called acute disseminated encephalitis) is often fatal.

AIDS patients and others at high risk can develop encephalitis due to parasites such as :- Certain roundworms, Cysticercosis- Toxoplasmosis- Malaria - Amoeba

Encephalitis may also be caused by bacteria such as :Lyme disease

LuesTuberculosis

Signs and Symptoms

Primary symptoms of encephalitis include sudden fever, stiff neck, malaise, photophobia and headache.

Infants may develop bulging of the fontanels of the skull.

Other early symptoms include the following: Abnormal sleep patterns Behavioral changesExhaustion Nausea Muscle stiffness Sore throat Upper respiratory tract infection (coughing,

sneezing)

Neurological complications that may be permanent or improves as the infections runs its course include the following :Altered mental state (e.g., disorientation,

personality changes) SeizuresPtosis, diplopia, strabismus Hyperactive deep tendon reflexes Increased intracranial pressure

Loss of consciousness Mental retardation Motor dysfunction Paresis of the extremities Projectile vomiting Pupil irregularities Tremor

Diagnosis

Medical history Including recent exposure to insects, travel, personality changes, and contact with unusual animals or illnesses.

Neurological examination 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 Blood and urine tests are used to isolate and identify viruses. Serology test to detect antibodies to a virus in the cerebrospinal fluid.Enzyme-linked immunosorbent assays (ELISA) can identify viruses that cause encephalitis soon after infection. Polymerase chain reaction (PCR) can identify small amounts of viral DNA. PCR becomes the mainstay of non invasive diagnosis.

Spinal tap

Opening pressure : elevatedPleocytosis of 10 – 1000 cells/mm3 ( usually lymphocyt )

Erythrocyt, xanthochromia frequently seen ( presence or absence not diagnostic )

Glucose : normal or mildly decreased

Protein : mildly elevated

Virus is rarely recovered from CSF

CT Scan may shows :- brain swelling - temporal hypodensity and contrast enhancement

MRI may shows :- temporal lobe pathology including loss of gray - white differentiation - brain swelling- hemorrhagic component

EEG may show focal slowing and spiking in the temporal lobe that are indicative of Herpes simplex encephalitis

Treatment

Treatment for encephalitis depends on the cause. With the exception of herpes simplex and varicella-

zoster encephalitis, the viral encephalitis is not treatable.

Some experts advise immediately giving Acyclovir, the standard treatment for herpes simplex encephalitis to all patients whose symptoms indicate encephalitis.

If herpes simplex encephalitis is suspected, antiviral medication such as acyclovir 10 mg/kg every 8 hours is administered intravenously immediately for 10 – 14 days to improve chances for recovery and prevent complications.

Palliative care may include :

- Antibiotics to prevent secondary infections

- Drug for reducing intracranial pressure :

furosemide, mannitol and corticosteroid - Anticonvulsant to prevent seizures :

Phenytoin, benzodiazepines (e.g., lorazepam)

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 herpes virus 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 arbo viral 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.