In multiple sclerosis (MS), the immune system attacks the protective covering of the nerves, leading to impaired sensory and motor nerve function, and in most cases some degree of disability Figure 01. The myelin sheath is a protective covering around a portion of nerve cells that allows the cells to transmit impulses quickly and effectively. In MS, the myelin sheath is damaged, causing varying symptoms that include increased difficulty moving and progressive weakness.
MS follows four basic courses: relapsing-remitting, secondary progressive, primary progressive, and progressive-relapsing. During the first course, which is called relapsing-remitting MS, your symptoms will come and go. On average, a person will have a relapse every two years. Approximately 15% of all patients will only have a single attack of MS, and then never have symptoms again. In addition, some people have MS that will follow a relapsing-remitting course, but their symptoms will not progress. In fact, symptoms do not progress during the first 10 years of diagnosis in 50% of patients with relapsing-remitting disease.
The second course, which is called secondary progressive MS, also follows a pattern of relapse and remission, but symptoms get worse with each relapse. Thirty to fifty percent of patients with relapsing-remitting MS will eventually develop secondary progressive MS.
Fewer than 15% of MS patients will develop the third form, which is called primary progressive MS. In this form, symptoms get worse over time, and there is no distinct relapse-remission pattern.This form of MS is most common in people whose symptoms begin after the age of 40.
The fourth and most rare course of disease is called progressive-relapsing MS. In this form, the disease steadily worsens with distinct relapse periods. Approximately 5% of MS patients are diagnosed with this form of the disease.
Figure 01. Normal Nerve Cell with Myelin Sheath
Multiple sclerosis is an autoimmune disease, meaning that it occurs when the body’s immune system attacks itself. In MS, white blood cells known as T-cells launch an attack against the myelin sheath. This causes other immune-system cells to flood the area, leading to inflammation, swelling, and ultimately damage to the myelin sheath. The blood-brain barrier, which normally prevents drugs and other substances from traveling from the blood to the brain, also becomes much more permeable, leading to swelling and other problems. The myelin develops scars, which makes it more difficult for nerve impulses to travel along the axon of the nerve cells.
Environmental and hereditary factors are known to play a role in MS. The geographic prevalence of MS decreases nearer the equator, suggesting that some type of environmental exposure plays a role in a person’s likelihood of developing the disease. Genetics are also involved in MS, as shown by the fact that people with a close relative with MS have an increased risk of developing the disease. Some ethnic groups have a higher risk of MS than others; in the US, the disease is more common among Caucasians. Several interacting genes in conjunction with environmental factors (rather than by the action of a single gene) probably cause MS.
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