What are meningitis and encephalitis?
Meningitis is an inflammation of the three membranes that cover the brain and spinal cord (the meninges). Encephalitis is an inflammation of the brain. Meningoencephalitis is an inflammation of both the brain and the meninges.
The meninges are layers of tissue that protect the central nervous system, which is comprised of the brain and the spinal cord. The central nervous system is also cushioned and protected by the watery fluid called cerebrospinal fluid (CSF) that surrounds the brain and flows between the meninges, in the spaces within the brain called ventricles, and along the spinal cord.
Meningitis and encephalitis result from infections of the central nervous system caused by a bacterium, virus, fungus, or parasite. These infections can be acute or chronic, and their severity can range from mild and self-limited to fatal. Their associated inflammation and swelling increase pressure on the brain and nerve tissue. This can hinder, or permanently damage, the function of nerves and the body systems that they control. Rarely, certain drugs can cause meningitis, and autoimmune disease can sometimes cause encephalitis.
Meningitis and encephalitis can disrupt the blood-brain barrier that separates the brain from circulating blood and regulates the distribution of substances between the blood and CSF. The blood-brain barrier helps keep large molecules, toxins, and most blood cells away from the brain. With the disruption of this barrier, white and red blood cells, immune system chemicals, toxins, increased amounts of protein, and the microorganism causing the inflammation may be found in the CSF. CSF is a clear, watery liquid that normally flows freely around the brain and spinal cord. With meningitis and encephalitis, the flow of CSF may slow or become obstructed, which can increase CSF pressure, increase pressure on the brain and spinal cord, and decrease blood flow to the brain.