Meningoencephalitis is an inflammation of both the brain and the meninges and encephalitis and meningitis often occur together. The resulting inflammation causes swelling of the affected areas of the brain which can cause increased pressure. This is because the brain is in a fixed compartment within the skull and has no room to expand. Therefore as the brain swells pressure starts to build up inside the brain. This pressure can affect or permanently damage the function of the nerves in the brain and damage the brain tissue itself. Therefore these diseases, if left untreated, can be fatal.
In addition to causing swelling that can cause pressure on the brain, meningitis and encephalitis can also damage the blood-brain barrier. This is a protective barrier that separates the specialised fluid found in the brain, called cerebrospinal fluid (CSF), from the blood that circulates around the brain. This protects the brain from certain foreign substances, toxins, chemicals and hormones in our blood stream that may be harmful to the brain. With the disruption of this barrier, white and red blood cells, immune system chemicals, toxins, increased amounts of protein, and the germs that cause inflammation can enter the cerebrospinal fluid (CSF). This then alters the consistency of the CSF which can cause this free flowing fluid to flow slowly. This combined with the swelling that occurs in meningitis and encephalitis can completely obstruct the flow of CSF. This can increase the CSF pressure which subsequently increases the pressure in the brain and spinal cord, and can decrease blood flow to the brain causing further injury.
Both meningitis and encephalitis are usually caused by infections. These may be bacterial, viral, fungal, or parasitic infection. Very rarely meningitis may be also be caused by surgery or other invasive procedures on the brain and this is called “chemical meningitis”. Encephalitis may also be caused by damage from the auto-immune system which will be discussed later. Most causes of meningitis and encephalitis however are caused by bacteria or viruses, with viral causes being the most common.
Meningitis and encephalitis can also be divided into whether they are acute, with a quick onset of symptoms, or chronic where symptoms can last a month or more. They can also be grouped into terms on their severity which can range from mild and self-limiting to fatal.