What is Multiple Sclerosis?
Multiple sclerosis (MS) is a complex brain disease that affects the central nervous system (CNS). The CNS includes the brain, spinal cord, and vision pathways. In MS, the immune system attacks the myelin sheath. This is the fatty tissue that surrounds and protects nerve fibers. It also attacks the nerve fibers themselves. This damage is called demyelination. The scar tissues that form when myelin is damaged are called sclerosis. They are also known as lesions or plaques.
When any part of the myelin sheath or nerve fiber is damaged or destroyed, nerve signals traveling to and from the brain and spinal cord get distorted or blocked. This causes many different symptoms. Sometimes the myelin can repair itself. MS symptoms go away after the immune attack or relapse. But over time, the myelin and nerve fibers cannot recover. They suffer permanent damage. This may cause a decline in how the body works. This depends on the disease course. Several MS disease courses have been identified.
Relapsing-Remitting MS
Relapsing-remitting MS (RRMS) is the most common MS disease course. About 85% of people with MS are first diagnosed with this course. It has clearly defined relapses followed by periods of partial or complete recovery with no clear worsening of MS disability between relapses.
MS relapses are also called "attacks," "exacerbations," or "flares." They are rapid, major worsening of existing symptoms or development of new symptoms. They last at least 24 hours and are not caused by infection, fever, or other stress. A relapse is different from the daily changes in symptoms. These changes are caused by varying function of the nervous system due to existing MS plaques. Unlike these daily changes, relapses are caused by new areas of inflammation and demyelination in the brain, spinal cord, or visual pathways. Most symptoms of relapses clear up with time, rest, and if needed, therapy. There are treatments that can speed up recovery from a relapse. However, if there is partial recovery, remaining symptoms can become permanent. MS relapses typically last a few days to weeks. If not taking a disease modifying therapy, people with RRMS typically have 1-3 relapses a year, although some people can go decades between relapses.
Infection, fever, and stress can all lead to major worsening of brain function that can look like an MS relapse. This is called a pseudo-relapse because, like daily changes, there is no new inflammation and demyelination occurring. A magnetic resonance image (MRI) can help tell the difference between MS relapses and pseudo-relapses. A pseudo-relapse is managed by treating the underlying infection or source of stress.
Primary Progressive MS
Primary progressive MS (PPMS) is marked by steady worsening of disease from the start without clear relapses. There may be changes in how fast it progresses or periods of stability during the course of the disease. About 15% of people with MS are first diagnosed with this course.
Secondary-Progressive MS
People with secondary-progressive MS (SPMS) are first diagnosed with RRMS and then transition to this progressive form of the disease. This course is marked by worsening of disability over years with fewer or no further relapses. Also, there are fewer or no new or enhancing plaques seen on MRIs. Not everyone with RRMS will transition to SPMS.
Clinically Isolated Syndrome
Clinically isolated syndrome (CIS) is a term that describes an event similar to a typical MS relapse. This happens in a person not previously diagnosed with MS. People who experience a CIS are at higher risk of developing MS. But not all go on to have MS.
