Encephalitis

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.

Viral
Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection. A common cause of encephalitis in humans is herpes simplex virus type I (HSE) which may cause inflammation of the brain. This can result in death. Other causes include infection by flaviviruses such as St. Louis encephalitis or West Nile virus, or by Togaviridae such as Eastern equine encephalitis (EEE), Western equine encephalitis (WEE) or Venezuelan equine encephalitis (VEE).

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 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).

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.

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).