encephalitis (inflammation of the brain)

Encephalitis is an inflammation of the brain. In most cases, this is triggered by an infection with viruses. If not only the brain itself but also the meninges are affected, this is called meningoencephalitis.

There is also the possibility of non-infectious inflammation of the brain, such as non-febrile acute disseminated encephalomyelitis (ADEM). This is thought to be caused by a faulty response of the body's immune system. Brain inflammations are to be distinguished from pure meningitis.

Most often, encephalitis is triggered by a viral infection. Two forms are distinguished:

• In the primary form, the viruses directly cause the inflammation of the brain.
• In the parainfectious form, the body's own immune system gets out of control and subsequently attacks the brain itself (autoimmune reaction). This faulty reaction is based on the fact that during an inflammation, antibodies against cell components of the brain (autoantibodies) have been formed, as a result of which the immune system now attacks the body's own structures in the brain.

Inflammation of the brain can be triggered by the following viruses, among others:

• Measles viruses
• Herpes viruses
• Mumps viruses
• Epstein-Barr viruses
• Influenza viruses
• Varicella zoster viruses
• TBE viruses (early summer meningoencephalitis viruses, which can be transmitted by a tick bite)

In addition, bacteria (for example, borrelia or tuberculosis bacteria), fungi, parasites, protozoa (trypanosomes), or certain autoimmune diseases can also lead to encephalitis.

Children, young adults and people with a weakened immune system (for example, due to HIV infection or immunosuppressive therapy) have a higher risk of developing encephalitis.

The symptoms of encephalitis are strongly dependent on the respective triggers of the inflammation, as many pathogens only affect certain brain regions. Depending on the affected brain region, the symptoms vary.

In the case of encephalitis triggered by viruses, general, flu-like symptoms such as fatigue, headache, fever and nausea occur at the beginning. As the disease progresses, various specific symptoms become apparent in addition to high fever:

• sudden impairment of the ability to concentrate and memory
• unconsciousness, confusion
• behavioural changes such as mood swings, paranoia, hallucinations or disorientation
• neurological deficits, for example speech disorders or paralysis of individual extremities or the eye muscles
• if the meninges are also irritated, stiffness and pain in the neck and back (meningismus signs)
• epileptic seizures

In order to diagnose encephalitis, the symptoms and medical history are first taken in a medical consultation (anamnesis). Details such as previous general illnesses, viral infections or tick bites are particularly important. Also holiday trips in the recent past as well as contact with farm animals or other persons with encephalitis are important. If necessary, additional attempts are made to obtain a second description from a relative or friend of the patient, as persons with encephalitis are often limited in their thinking, perception, and ability to communicate.

A detailed physical (bodily) and neurological examination is then performed. Here, in addition to the symptoms described, skin symptoms or disturbances of the water balance are sometimes detected.

If encephalitis is suspected, a sample of cerebrospinal fluid (CSF) is taken by lumbar puncture and examined in the laboratory for the presence of pathogens or signs of inflammation. The exact nature of the pathogen can be determined with the aid of a polymerase chain reaction (PCR), as even the smallest amounts of virus particles are sufficient to determine the cause of the disease. However, since the pathogens of encephalitis are often only detectable after a longer period of time and the cerebrospinal fluid is still free of pathogens in the acute phase of the brain inflammation, the diagnosis "encephalitis" is made in many cases on the basis of the characteristic symptoms. Only at a later stage is the diagnosis confirmed by laboratory diagnostics.

Normally, if encephalitis is suspected, a computer tomography (CT) scan is also performed to rule out other brain diseases such as cerebral haemorrhage. Magnetic resonance imaging (MRI) may also be used. In order to better visualize the consequences of the inflammation on brain function already in the early stages of the disease, electroencephalography (EEG) is often performed.

Since encephalitis is a severe disease with a high risk of complications, patients must always be treated and observed as inpatients in hospital. Life-threatening complications can be detected and treated more quickly in this way. The actual therapy varies depending on the cause of the encephalitis.

In the case of encephalitis, it is particularly important to start treatment immediately to prevent the brain from suffering damage from the inflammation. Since the exact nature of the pathogen is often not yet known when the diagnosis is made, a combination of various antibiotics (drugs against bacteria) and virustatics (drugs against viruses) is administered at the beginning of the therapy. If after some time the exact pathogen could be determined in the laboratory, the ineffective drugs are discontinued and the treatment is continued specifically with the most effective drugs.

If the encephalitis is due to a viral infection, viral drugs are used. As an example, the active substance aciclovir would be effective in the case of herpes encephalitis or varicella encephalitis, and a combination of ganciclovir and forscamet would be conceivable in the case of cytomegalovirus encephalitis. Antifungal (antifungal) medications are used for fungal infections. The earlier the drugs are given, the better the prognosis.

Antiepileptic drugs (drugs for epileptic seizures) are prescribed to lower intracranial pressure, if necessary. Antipyretic drugs or painkillers may also be necessary.

The prognosis of encephalitis is highly dependent on the severity of the disease as well as the type of pathogen. If the disease is diagnosed and treated early, the chances of recovery are usually quite good.

Even the very severe encephalitis caused by herpes simplex viruses can nowadays be treated well with medication, so that more than 80 percent of patients recover. In some cases, however, irreversible damage to the nervous system remains. Since the timing of the start of treatment is crucial for a favourable prognosis, indications such as sudden onset of high fever or disturbances of consciousness should be taken seriously and clarified by the doctor immediately.

A safe method of preventing encephalitis that occurs in the context of measles, mumps, rubella or polio is a vaccination against the respective viruses. There are also vaccinations for other pathogens, which are particularly useful for people who live in endangered areas or want to travel there. Examples of this would be vaccinations against the TBE virus (early summer meningoencephalitis virus) in tick areas or vaccinations against Japan B encephalitis, which is common in rural areas in Southeast Asia.

In some cases, the administration of antibodies (immunoglobulins) may also be helpful in reducing the severity of encephalitis. Even if the affected person has already been exposed to the pathogen, antibody treatment can be very effective - but therapy should be started as early as possible.