Encephalitis

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

Encephalitis is an acute inflammation of the brain.

Encephalitis with meningitis is known as meningoencephalitis.

Signs and symptoms

Patients with encephalitis suffer from fever, headache and photophobia with weakness and seizures also common. Less commonly, stiffness of the neck (nuchal rigidity) can occur with rare cases of patients also suffering from stiffness of the limbs, slowness in movement and clumsiness depending on which specific part of the brain is involved. Nuchal rigidity may lead to a misdiagnosis of meningitis, but treatment is the same. The symptoms of encephalitis are caused by the brain's defense mechanisms activating to get rid of the infection. Other symptoms can include drowsiness and coughing.

Cause

Viral

Viral encephalitis can be due either to the direct effects of an acute infection, or as one of the sequelae of a latent infection. A common cause of encephalitis in humans is herpes (HSE). It causes inflammation of the brain.

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.

Another cause is granulomatous amoebic encephalitis.

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 meningoncephalitis. 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).

Treatment

Treatment is usually symptomatic. Reliably tested specific antiviral agents are available only for a few viral agents (e.g. acyclovir for herpes simplex virus) and are used with limited success for most infection except 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. Anticonvulsants are used to prevent seizures.

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 Parkinsons 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).

See also

• Awakenings
• Rasmussen's encephalitis

References

www.ncbi.nlm.nih.gov 1: Neurology. 1991 Feb;41(2 ( Pt 1)):228-33. Related Articles, Links Hashimoto's encephalopathy: a steroid-responsive disorder associated with high anti-thyroid antibody titers--report of 5 cases. Shaw PJ, Walls TJ, Newman PK, Cleland PG, Cartlidge NE. Department of Neurology, University of Newcastle upon Tyne, UK.

External links

• Encephalitis.info resource providing evidence based support to people affected and professionals
• WHO: Viral Encephalitis
• eMedicine-1 and eMedicine-2 Information on the causes, symptoms, and treatment options for Encephalitis.
• Encephalitis Global, Inc. Website offering information and support to encephalitis survivors, caregivers and loved ones. Encephalitis Global Inc. is a USA 501(c)(3) public charity; annual FACES Encephalitis Conference information available at the website.
• A case study of a Limbic Encephalitis patient
• Meningitis and Encephalitis Information Page at NINDS
• Information on Encephalitis from Headway - the brain injury association UK based charity providing information and support