Multiple sclerosis (MS) is a chronic (long-term), progressive, degenerative disorder that affects nerve fibers in the brain and spinal cord. Multiple sclerosis is widely believed to be an autoimmune disease, a condition in which the immune system attacks components of the body as if they are foreign.
A fatty substance, called myelin, surrounds and insulates nerve fibers and facilitates the conduction of nerve impulse transmissions. MS is characterized by damage to myelin (called demyelination) caused by the destruction of specialized cells (oligodendrocytes) that form the myelin. Demyelination causes scarring and hardening (sclerosis) of nerve fibers usually in the spinal cord, brain stem, and optic nerves, which slows nerve impulses and results in weakness, numbness, pain, and vision loss.
Because different nerves are affected at different times, MS symptoms often worsen, improve, and develop in different areas of the body. Early symptoms of the disorder may include vision changes, such as blurred vision or blind spots, and muscle weakness.
MS can progress steadily or cause acute attacks (exacerbations) followed by partial or complete reduction in symptoms (remission). Most individuals with the disease have a normal lifespan.
MS affects over 250,000-500,000 people in the United States and may affect 2.5 million people worldwide. Northern Europe and the northern United States have the highest prevalence, with more than 30 cases per 100,000 people. Multiple sclerosis affects two to three times as many women as men, and affects Caucasians more often. Most individuals experience their first signs or symptoms between ages 20 and 40. Children of parents with MS have a higher rate of incidence (30-50%). Heredity does play a role in the development of MS.
Multiple sclerosis is unpredictable and varies in severity. In some individuals, multiple sclerosis is a mild illness, but it can lead to permanent disability in others. Treatments can modify the course of the disease and relieve symptoms.
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types of multiple sclerosis
Multiple sclerosis is classified according to frequency and severity of neurological symptoms, the ability of the CNS to recover, and the accumulation of damage.
Primary progressive MS: Primary progressive MS causes steady progression of symptoms with few periods of remission. With primary progressive MS, symptoms get worse over time, but there are no relapses or remissions. Some people with primary progressive MS have brief periods of time during which their symptoms either stay the same or improve slightly. This type of MS is most often diagnosed in people over the age of 40.
Relapsing-remitting MS: In relapsing-remitting MS, symptoms come (relapses) and go (remissions). Symptoms may evolve over several days and then disappear, although some symptoms may remain. The course varies from person to person, but on average, relapses appear every two years. The period between relapses can be very long, as much as 20 years or more. A small percentage of people have only a single attack in their lifetime.
Relapsing-remitting MS is the most common form of the disease and is most frequently diagnosed between the ages of 20-40. Up to 80% of individuals with MS are diagnosed with the relapsing-remitting type. Only 50% of people with RR MS develop secondary progressive MS within the first 10 years.
Secondary progressive MS: Secondary progressive MS is initially similar to relapsing-remitting MS and eventually progresses to MS with no remission. The change from relapsing-remitting MS to secondary progressive MS generally occurs five to 15 years after the disease begins. With secondary progressive MS, neurological symptoms tend to worsen progressively, with or without superimposed relapses. Over time, it is common for secondary progressive patients to have fewer attacks (sometimes none at all), despite continual progression. About 30% of individuals with MS have secondary progressive disease.
Relapsing-progressive MS: Relapsing-progressive MS is a rare form of MS with a gradual worsening of symptoms from the beginning, with superimposed relapses and remissions.