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.
Signs and symptoms 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.
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, varicella zoster virus, and JC virus.
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, Western equine encephalitis virus or Venezuelan equine encephalitis virus, variola
minor virus and variola major virus.
Henipaviruses; Hendra and Nipah, are also known to cause viral encephalitis.
Bacterial and other It can be caused by a bacterial infection,
such as bacterial meningitis, spreading directly to the brain, or may be a complication of
a current infectious disease syphilis.
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.
Limbic system encephalitis In a large number of cases, called limbic
encephalitis, the pathogens responsible for encephalitis attack primarily the limbic system.
Autoimmune encephalitis
It has recently been recognised that there are types of encephalitis resulting from an
attack of the brain by the body's immune system.
These autoimmune conditions include but are not limited to VGKC antibody associated encephalitis,
Anti-GAD antibody associated encephalitis, NMDA receptor antibody associated encephalitis,
and Hashimoto's encephalitis.
The majority of patients with autoimmune encephalitis do not harbor a tumor and the etiology of
the disease in these patients is less clear, often leading to a delayed diagnosis.
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.
Neurologist Oliver Sacks used the Parkinson's drug L-DOPA to revive those still alive in
the late 1960s.
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.
Diagnosis 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 or by polymerase chain reaction that amplifies the RNA or DNA of
the virus responsible.
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 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 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 Vaccination is available against tick-borne
and Japanese encephalitis and should be considered for at-risk individuals.
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 has had contact with chicken pox virus should be given prophylaxis
with hyperimmune zoster immunoglobulin.
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.
During 2010 it caused about 120,000 deaths, down from 144,000 in 1990.
Herpes simplex encephalitis has an incidence of 2–4 per million population per year.
See also Rasmussen's encephalitis
Bickerstaff's encephalitis La Crosse encephalitis
Wernicke's encephalopathy Meningitis
Cerebritis References
External links The Encephalitis Society - A Global resource
on Encephalitis Autoimmune Encephalitis Alliance
WHO: Viral Encephalitis Encephalitis Global Inc.
- A USA charity sharing information and support