What is Encephalitis?...

Encephalitis is an inflammation of the brain.  Encephalitis can be caused by either an infection invading the brain (infectious) or through the immune system attacking the brain

Causes of encephalitis

Viruses are the most common infectious cause of encephalitis.  Herpes Simplex Virus is the most frequently identified viral agent leading to viral encephalitis, however in rare circumstances, the common cold, tummy infection, skin rash and other minor infections may affect the brain.

More rarely bacteria, fungus and parasites can cause encephalitis

Non-infectious encephalitis can occur in two forms.  Sometimes the body’s reaction to a virus itself can lead to encephalitis.  This occurs when the immune system tries to fight off the virus and by mistake attacks the brain at the same time.

In some cases the immune system will create antibodies to attack abnormal tissue within the body (e.g. cancerous tissue). Unfortunately, a few of these antibodies may react against the patient’s healthy tissue proteins, attacking the tissue and causing an autoimmune disease.  This is known as Paraneoplastic Limbic Encephalitis.

Finding a specific antibody in the blood can identify other autoimmune causes of encephalitis, even though the trigger in these cases may not be known.

Symptoms

The symptoms of encephalitis are wide ranging because they are dependant upon the specific area of the brain affected by the inflammation

Typically encephalitis frequently begins with a ‘flu like illness which quickly develops into an illness with high fever, severe headaches, nausea, vomiting and an altered level of consciousness.  This can range from mild confusion or drowsiness, to loss of consciousness and coma.

Other symptoms include a high temperature, seizures, aversion to bright lights, inability to speak or control movements, sensory changes, neck stiffness or general uncharacteristic behaviour.

Diagnosis

There are a number of disorders that mimic the neurological symptoms of encephalitis including bacterial meningitis, stroke, brain tumours to name but a few.  Therefore clinical observations alone cannot readily distinguish encephalitis from other disorders and as a result a variety of hospital tests are often required.

A number of standard tests are often run in the early stages of suspected encephalitis.  Not all tests are required to identify encephalitis and the tests are not run in a particular order.  The common tests include:

Scans

Computerized Tomography (CT), Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) are types of scanning techniques used in the identification of encephalitis. 
CT scanning is used primarily as a screening examination to check for subtle changes in the brain and more importantly rule out other conditions such as tumours or strokes.
MRI offers more detailed imaging results and is the imaging technique of choice in determining encephalitis.
PET is a nuclear medicine imaging technique, which produces a three-dimensional image or map of functional processes in the body.  PET scanning is often considered the gold standard in imaging techniques, however the cost, complexity and availability of PET scanners means it is used infrequently.

Electroencephalogram (EEG)

The electrical activity produced by the brain is measured using electrodes placed on an individuals scalp.  The brain waves will often include abnormal patterns of activity when encephalitis is present.

For some individuals diagnosis of encephalitis will be based on the exclusion of other diseases, which have been dismissed under laboratory tests.  In particular for most cases the actual type of encephalitis infectious or non-infectious will have been determined.

In conjunction with the above clinical tests the history is of prime importance in the assessment of a patient with suspected viral encephalitis. 

The geographical location and travel history of the patient may offer clues as to the cause of the encephalitis.  Travellers from Asia may be infected with Japanese encephalitis, cerebral malaria should be considered in cases where patients have recently returned from Africa.

Considerations of recent illnesses, rashes within the family or in the community may also assist in the diagnosis.  Measles, mumps, chicken pox, parvovirus though occasionally can all cause encephalitis.

Lumbar Puncture (LP)

A LP is a procedure, which involves passing a needle under local anaesthetic between two of the backbones at the base of the spine in order to extract a sample of cerebrospinal fluid (CSF).

Obtaining a CSF sample is essential tool in clinical investigations, since CSF samples can reveal whether or not there is an infection present and whether it is likely to be a bacterial or viral infection.

The CSF sample can also be used to run further more complex tests such as the Polymerase Chain Reaction (PCR).  PCR is used to identify the genetic material of the infection and therefore therapy can be tailored to treat the specific infection.

Chronic / Subacute Infectious Encephalitis

Measles virus – Subacute Sclerosing Panencephalitis (SSPE)
Rubella virus – Progressive Rubella Panencephalitis
JC virus – causing Progressive Multifocal Leukoencephalopathy (PML)

Infectious Encephalitis

Herpes Simplex
West Nile
Japanese
Tick-borne
Mycoplasma
West Nile

Non-infectious / Post infectious Encephalitis

Acute Disseminated Encephalomyelitis (ADEM)
Encephalitis Lethargica (EL)
Hashimoto’s Encephalitis
Paraneoplastic Limbic Encephalitis
Voltage Gated Potassium Channel Antibody Limbic Encephalitis
Rasmussen’s Encephalitis

Treatment

Encephalitis is a very serious condition requiring prompt treatment; the earlier the treatment the greater the possibility of reducing both mortality and disability.  It is for this reason that patients are often given several different drugs at once and sometimes before the condition is accurately diagnosed.

Treatment of viral encephalitis

Acyclovir is the most frequently used anti viral drug and is effective against Herpes Simplex and Varicella Zoster viruses.  Acyclovir is given as a high dose intravenously (via the veins).  It is normally given over a period of 14 to 21 days.

Unfortunately there are no specific treatments for many other viral causes of encephalitis however a number of drugs have been used in the treatment of encephalitis.

Ganciclovir – HHV-6 induced encephalitis
Ribavarin – Rabies and measles induced encephalitis
Cidofovir – a general treatment of viral encephalitis
Interferon Alpha – measles induced encephalitis
Intravenous Immunoglobulin (IVIG) –
IVIG is a plasma protein replacement therapy for immunosuppressed patients.  IVIG is administered to maintain adequate/improve antibody levels to prevent/attack infections

Treatment of bacterial encephalitis

There is a range of antibiotic treatments available for bacterial encephalitis.  Usually patients are given a broad-spectrum antibiotic intravenously.  If the specific bacterial agent is identified then the specific antibiotic will be given.

Treatment of non-infectious/post infectious encephalitis

These treatments involve suppressing the patient’s immune system, since this type of encephalitis is caused by the immune system attacking the brain.

Such treatments include:

Corticosteriods – are sometimes used to reduce the inflammatory response and suppress the immune system in order to prevent the attacks on the brain.  Sometimes Corticosteriods are used in conjunction with plasma exchange therapy.

Plasma exchange - is used predominantly as a therapy for autoimmune disorders.  A specialist machine extracts blood from the patient and separates plasma from the blood cells in order to remove the disease-causing antibodies from the patients’ blood.  Plasma exchange offers the quickest short-term answer to removing harmful antibodies; however, the production of antibodies by the immune system must also be stopped, usually by the use of medications that suppress the immune system, such as Prednisone, Cyclophosphamide, Rituximab to name but a few.

Removal of tumour – the removal of the tumour together with immunosuppression therapy may help the treatment of Paraneoplastic Limbic Encephalitis.