Encephalitis

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Encephalitis is an inflammatory disease of the brain. There are many infectious and non-infectious causes of encephalitis. Most cases of encephalitis are mild and self-limited in healthy people. Encephalitis can, however, sometimes lead to severe disease, disability, and death.

Magnetic resonance image of the brain, the organ affected by encephalitis. Source: WikiMedia Commons.

Contents

Types

Encephalitis

Encephalitis refers to inflammation of the brain by infectious and non-infectious causes.

Meningoencephalitis

Meningoencephalitis is a term used to refer to involvement of both the meninges and the brain tissue at the same time. Many diseases classified as meningitis (inflammation of the tissues surrounding the brain) or encephalitis often involve both areas of the central nervous system, and an overlap in signs and symptoms can be seen in these situations.

Meningovascular encephalitis

Meningovascular encephalitis refers to inflammation of the blood vessels in the brain with involvement of surrounding brain tissue. This is the form seen in encephalitis caused by syphilis.

Postinfectious encephalitis

Postinfectious encephalitis is characterized by the sudden onset of depression of consciousness, seizures, and other symptoms of encephalitis, 2 to 12 days after an infection has occurred in another part of the body. This has been reported after infection with rubella, influenza, mumps, measles, Epstein-Barr virus, and Herpes zoster virus.

Signs and Symptoms

Encephalitis usually has a slower onset than acute meningitis, but sometimes symptoms can develop rapidly. The course of illness can be relatively short (days to weeks) or can be prolonged (months). Time to onset of symptoms (incubation period) and length of illness depend on the cause of the encephalitis.

Because encephalitis is an inflammation of the brain, symptoms often involve levels of consciousness and state of mind. Symptoms can include the following:

  • Fever
  • Confusion
  • Change in personality
  • Nausea and vomiting
  • Lethargy
  • Seizures
  • Weakness in the muscles
  • Tremors
  • Trouble speaking
  • Difficulty thinking
  • Stupor
  • Coma

In children less than two years of age, symptoms can start suddenly and include high fever, convulsions, rigidity of extremities, drowsiness, and abnormal reflexes.

Symptoms can be mild or severe, and the disease process can be self-limited, requiring only supportive therapy, or can lead to death.

Causes

The list of agents and conditions that can cause encephalitis is quite long. Some of the more common causes are listed below.

Infectious causes

Photomicrograph of brain tissues showing a cyst of Acanthamoeba sp., a free-living ameba capable of causing encephalitis. Source: CDC/George Healy, Ph.D.

Viral

Most cases of infectious encephalitis are caused by a virus.

Other infectious agents

Non-infectious causes

Diagnosis

The two most important aspects to the diagnosis of encephalitis are the clinical presentation of the patient and examination of a sample of cerebrospinal fluid (CSF). CSF is fluid that circulates around the brain and spinal cord.

Examination of a sample of CSF involves a procedure called a lumbar puncture. This is usually a painless procedure where a small amount of CSF is removed at the base of the spine using a small needle. In people who have meningitis and encephalitis, there are usually several abnormal findings seen on examination of the CSF. These include an elevated white blood cell count, a low sugar content, and a high protein content. The CSF can also be stained and cultured to look for microbial pathogens. There are also rapid diagnostic immuno assay tests that can be done on CSF to quickly determine the cause of the disease.

Tests on blood samples can be done to look for viral causes of encephalitis. Test results often take several days, however.

Radiography such as magnetic resonance imaging (MRI) and cranial computed tomography (CT) is less important in the very early stages of encephalitis as a diagnostic tool, compared with clinical exam and CSF examination. However, it does play a role in cases where the diagnosis is not clear, or where there are complications, such as a brain abscess.[3]

Treatment

There are no effective antimicrobial agents for most viral causes of encephalitis and the great majority of these diseases are self-limited and resolve with supportive therapy. Acyclovir and related drugs are used for the treatment of Herpes simplex encephalitis.

Effective antimicrobials are available for some other infectious causes such as fungi, tuberculosis, bacteria, and some parasites.

Supportive therapy is important in the management of these diseases. There has been research on the use of agents to prevent or lessen brain swelling which can occur with either meningitis or encephalitis. The value of treatment with dexamethasone, a corticosteroid, has been demonstrated in children with meningitis caused by Haemophilus influenzae, and in adults with Streptococcus pneumoniae meningitis,[4] [5] although the topic is still controversial.[6]

Prevention

Many forms of encephalitis are transmitted to humans by insect vectors. Using insect repellents on skin and clothing can help prevent insect bites and infection with these viruses. Removing standing water from buckets, birdbaths, pet dishes, pots, tires, wading pools, and other reservoirs of water around the home help eliminate mosquito breeding areas. Mosquitoes can be repelled from skin using insect repellant that contains DEET or picaridin. According to the American Academy of Pediatrics, DEET is safe and effective in young children when used according to directions and when certain precautions are taken. [7] Pets should not be treated with DEET because they may ingest it after licking their fur. Mosquito nets are also effective, as is taking precautions during the early morning and evening when the mosquitoes are more likely to bite.

Other forms of viral encephalitis can be transmitted by the fecal-oral route. Good hygiene practices, such as vigorous hand washing, can help prevent such cases.

How Encephalitis is Spread

The treehole mosquito transmits the virus that causes La Crosse encephalitis. Source: CDC.
Viral causes of meningitis and encephalitis can be spread by insect vectors. Such cases include West Nile virus, St. Louis encephalitis, Eastern equine encephalitis, and La Crosse encephalitis. Other causes of this disease can be spread by coming in contact with fecal matter contaminated with viruses that can cause encephalitis, including coxsackievirus, echovirus, and poliovirus.

Non-viral causes of encephalitis are generally spread by the same mechanism as the underlying disease. For example, syphilis causes meningovascular encephalitis and is spread through sex. Naegleria, a parasite that can infect the brain, is spread in fresh water. Cat-scratch disease (an uncommon cause of encephalitis) is spread by a scratch or bite from cats (usually non-domestic cats).

Clinical Trials

Clinical research trials are ongoing in the areas of encephalitis. Visit ClinicalTrials.gov for more information.

Expected Outcome

Most people who develop viral encephalitis recover with supportive therapy. The mortality rate ranges from 5%-30% depending on the causative agent and the age of the subject; the elderly tend to have a higher death rate. Occasionally, long-term disabilities can result from encephalitis.

References

  1. Bristow MF, Kohen D. Neuroleptic malignant syndrome. Br J Hosp Med. 1996 Apr 17-30;55(8):517-20. Abstract
  2. Glass JP, Lee YY, Bruner J, Fields WS. Treatment-related leukoencephalopathy. A study of three cases and literature review. Medicine (Baltimore). 1986 May;65(3):154-62. Abstract
  3. Fitch MT, Abrahamian FM, Moran GJ, Talan DA. Emergency department management of meningitis and encephalitis. Infect Dis Clin North Am. 2008 Mar;22(1):33-52, v-vi. Abstract
  4. de Gans J, van de Beek D. Dexamethasone in Adults with Bacterial Meningitis. N Engl J Med. Abstract | Full Text
  5. Ozen M, Kanra G, Kara A, et al. Long-term beneficial effects of dexamethasone on intellectual and neuropsychological outcome of children with pneumococcal meningitis. Scand J Infect Dis. 2006;38(2):104-9. Abstract
  6. Mongelluzzo J, Mohamad Z, Ten Have TR, Shah SS. Corticosteroids and mortality in children with bacterial meningitis. JAMA. 2008 May 7;299(17):2048-55. Abstract
  7. American Academy of Pediatrics. West Nile Virus Information. Accessed My 7, 2008

External Links

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