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What is Multiple Sclerosis?

By Sylvia Klineova, M.D. ; Updated August 14, 2017

Multiple sclerosis, or MS, is a neurological condition that affects the brain and the spinal cord. It is a chronic, lifelong condition in which certain parts of the nervous system are targets for inflammation and demyelination. Multiple sclerosis affects more than 400,000 people in United States and is the highest cause for non-traumatic neurological disability in young adults. It typically begins and is diagnosed between ages 20 and 50; in only a very small amount of people does the disease start before age 10 or after age 60.

Multiple sclerosis affects women more often than men and is found predominantly in Caucasians. It is also found more frequently in the Northern hemisphere.

Multiple sclerosis can cause various neurological symptoms, and if left untreated the disease will, in the majority of people, lead to permanent disability.

Inflammation and Demyelination

The key processes of MS are inflammation and demyelination caused by the white blood cells (the T and B cells). In people without MS, these cells cause immune reactions and protect them from viruses, bacteria or cancer cells. For people with MS, however, these immune cells attack the body's nerve cells and cause the destruction of the myelin.

Nerve cells require myelin to function properly. Nerve cells are similar to electrical cables in that they require sheaths of insulation called myelin. Myelin is crucial for the signals to travel through the body without interruption and at a certain speed. During the demyelination, myelin is destroyed by a process called inflammation caused by the immune cells. The inflammation usually lasts a few weeks, after which the body starts to remake the myelin and nerve cells regain their function.

Demyelinated nerve endings are not only unable to function properly, but they also lack a source of nourishment, which leads to further damage.

Multiple Sclerosis Subtypes

Based on how the disease runs its course, we divide MS into the three subtypes: relapsing-remitting, secondary progressive and primary progressive. The first neurological event in the MS course is called clinically isolated syndrome. While we try to fit every person within one of the categories, this disease is very different for everyone, and even patients in the same category do not have the identical disease course or response to the treatment.

Clinically Isolated Syndrome

This term is used to describe a first neurological event caused by inflammatory changes in either the brain or spinal cord. Different events can be experienced, but the most frequent ones are inflammation in the optic nerve causing decreased vision and eye pain, changes in sensation in arms, legs or torso, ability to feel, double vision and problems with balance. This first event suggests risk of developing further events leading to a diagnosis of MS, and further brain and spine imaging testing helps to determine how high this risk is.

Relapsing-Remitting MS

The majority of MS patients belong to this category and during the course of their disease will experience periodic relapses (times of disease activity) and remissions (times of quiescence). Inflammation and demyelination are the hallmark processes of the relapse period. During a typical relapse, patients experience various neurological impairments, such as weakness, numbness, balance problems or vision problems. Remission is generally a quiet time with no new activity, but patients can still notice brief reappearances of previously experienced symptoms.

Secondary Progressive MS

This subtype of MS is characterized by slow and gradual progression of neurological impairments, and it usually starts after years of relapsing-remitting MS. Patients usually notice a slow and gradual progression of already-present symptoms, increased numbness or weakness, increased problems with walking and balance and the need for a cane or walker. Daily tasks like walking to the store can become challenging and herald the progressive phase. This progression is sometimes difficult to grasp because symptoms can fluctuate and change from month to month. A definitive progression is usually established by evaluating changes present for the past six months to a year.

Primary Progressive MS

Progression of the disease starts from the onset in this MS subtype, and we cannot identify any periods of relapses and remissions. Contrary to its name, progression in PPMS can be slow, and some patients do reach a plateau with stable neurological status. But disability does increase over time.

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