Encephalitis

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Encephalitis
Classification and external resources
Coronal T2-weighted MR image shows high signal in the temporal lobes including hippocampal formations and parahippogampal gyrae, insulae, and right inferior frontal gyrus. A brain biopsy was performed and the histology was consistent with encephalitis. PCR was repeated on the biopsy specimen and was positive for HSV
ICD-10	A83-A86, B94.1, G05
ICD-9	323
DiseasesDB	22543
eMedicine	emerg/163
MeSH	D004660

Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue. More advanced and serious symptoms include seizures or convulsions, tremors, hallucinations, and memory problems.

Cause

Viral

Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection. The most common causes of acute viral encephalitis are rabies virus, Herpes simplex, poliovirus, measles virus, and JC virus.^[1] Other causes include infection by flaviviruses such as Japanese encephalitis virus, St. Louis encephalitis virus or West Nile virus, or by Togaviridae such as Eastern equine encephalitis virus (EEE virus), Western equine encephalitis virus (WEE virus) or Venezuelan equine encephalitis virus (VEE virus).

Bacterial and other

It can be caused by a bacterial infection, such as bacterial meningitis, spreading directly to the brain (primary encephalitis), or may be a complication of a current infectious disease syphilis (secondary encephalitis). Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Lyme disease and/or Bartonella henselae may also cause encephalitis. Cryptococcus neoformans is notorious for causing fungal encephalitis in the immunocompromised. Streptococci, staphylococci and certain Gram-negative bacilli cause cerebritis prior to the formation of a brain abscess.

Autoimmune disease may also cause encephalitis.^[2]

Diagnosis

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, poor appetite and fever.

Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningoencephalitis. Examination of the cerebrospinal fluid obtained by a lumbar puncture procedure usually reveals increased amounts of protein and white blood cells with normal glucose, though in a significant percentage of patients, the cerebrospinal fluid may be normal. CT scan often is not helpful, as cerebral abscess is uncommon. Cerebral abscess is more common in patients with meningitis than encephalitis. Bleeding is also uncommon except in patients with herpes simplex type 1 encephalitis. Magnetic resonance imaging offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may show sharp waves in one or both of the temporal lobes. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination. Diagnosis is often made with detection of antibodies in the cerebrospinal fluid against a specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible (such as varicella zoster virus). Serological tests may show high antibody titre against the causative antigen.

Treatment

Treatment is usually symptomatic. Reliably tested specific antiviral agents are few in number (e.g. acyclovir for herpes simplex virus) and are used with limited success in treatment of viral infection, with the exception of herpes simplex encephalitis. In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important. Corticosteroids (e.g., methylprednisolone) are used to reduce brain swelling and inflammation. Sedatives may be needed for irritability or restlessness. For Mycoplasma infection, parenteral tetracycline is given. Encephalitis due to Toxoplasma is treated by giving a combination of pyrimethamine and sulphadimidine.

Prevention

Post-infectious encephalomyelitis complicating small pox vaccination is totally avoidable now as small pox is now eradicated. Contraindication to Pertussis immunisation should be observed in patients with encephalitis. An immunodeficient patient who have had contact with chicken pox virus should be given prophylaxis with hyperimmune zoster immunoglobulin.

Encephalitis lethargica

Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1918 to 1930. Those who survived sank into a semi-conscious state that lasted for decades until the Parkinson's drug L-DOPA was used to revive those still alive in the late 1960s by Oliver Sacks.

There have been only a small number of isolated cases in the years since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be either a bacterial agent or an autoimmune response following infection.

Limbic system encephalitis

In a large number of cases, called limbic encephalitis, the pathogens responsible for encephalitis attack primarily the limbic system (a collection of structures at the base of the brain responsible for emotions and many other basic functions).

Epidemiology

The incidence of acute encephalitis in Western countries is 7.4 cases per 100,000 population per year. In tropical countries, the incidence is 6.34 per 100,000 per year.^[3]

Herpes simplex encephalitis has an incidence of 2–4 per million population per year.^[4]

See also

• Awakenings
• Chronic Fatigue Syndrome aka Myalgic Encephalomyelitis
• Rasmussen's encephalitis

Mystery illness - ovarian teratoma associated encephalitis(audio report)

References

• Shaw PJ, Walls TJ, Newman PK, Cleland PG, Cartlidge NE (February 1991). "Hashimoto's encephalopathy: a steroid-responsive disorder associated with high anti-thyroid antibody titers—report of 5 cases". Neurology 41 (2 (Pt 1)): 228–33. PMID 1992366. 

External links

• WHO: Viral Encephalitis
• Meningitis and Encephalitis Information Page at NINDS
• MR & CT scan diagnosis of HSV encephalitis Medical Image Database