Multiple Sclerosis (MS), chronic, unpredictable, and often progressive disease of the central nervous system that attacks and destroys tissues in the brain and spinal cord. There are several forms of MS, but all forms affect nerve function, resulting in problems ranging from mild numbness and difficulty walking to paralysis and blindness.
MS results from a misdirected immune-system attack leveled primarily against myelin, a white, fatty material that coats wirelike nerve fibers in the central nervous system. Myelin provides insulation that speeds the transmission of nerve signals relaying information into, within, and out of the brain and spinal cord. When myelin is attacked and destroyed in MS, a process known as demyelination, nerve transmission flow is interrupted, resulting in a variety of neurological problems.
The site of myelin attack often dictates the nerve circuitry affected, and therefore the symptoms that are experienced. For example, if demyelination occurs in the nerve circuitry that carries messages between the muscles and the brain, then it may cause problems with movement. If demyelination occurs in the nerves that carry sensory information to the brain, MS may cause problems with sensory functions, such as vision. There is also evidence that, in addition to the myelin sheath surrounding the nerves, the nerve fibers themselves may be attacked at some point during the course of the disease.
Although MS can occur at almost any age, the disease usually strikes people who are between the ages of 20 and 40. For unknown reasons, MS is more common in Caucasians, women, and people living in temperate, rather than tropical, climates. The Multiple Sclerosis International Federation estimates that up to 2.5 million people in the world have MS, and according to statistics gathered by the National Multiple Sclerosis Society, approximately 400,000 people in the United States have the disease.
Propagation of a Nerve ImpulseThis animation depicts nerve impulse transmission in a person with a healthy nervous system. In multiple sclerosis, destruction of myelin, the white fatty material that coats and insulates nerve fibers in the central nervous system, interrupts nerve impulse transmission. This results in a variety of neurological problems, depending on the nerves affected.© Microsoft Corporation. All Rights Reserved.
The cause of MS is unknown, but genetics, an infectious agent, a faulty immune system, or a combination of these factors appears to play a role in why a person contracts the disease. While there is no evidence that MS is directly inherited, relatives of those with MS have a slightly increased risk of developing the disease. Identical twins of people with MS do not always get MS. Because identical twins share all the same genes another nonhereditary factor must play a role in triggering the disease. Researchers have identified two genes that appear to be associated with multiple sclerosis. Both genes contain the instructions for producing interleukin receptors—proteins on the surface of immune-system cells.
Epidemiological studies suggest this second factor is encountered early in life—probably before reaching puberty. Studies have shown that MS is more prevalent in people who spend their first 15 years of life in a temperate climate than in those who live their first 15 years in a tropical climate. Many believe that the second factor is an infectious agent, such as a virus or bacterium. But after years of study, no single infectious agent has been shown to trigger MS. Some experts propose that MS is not triggered by a single infectious culprit, but instead by the way a person’s immune system reacts to an infection.
Studies suggest that MS is an autoimmune disease, in which the immune system attacks the body’s own tissue. New information about the way the immune system may be fooled into attacking its own tissue enforces this possibility. Certain bacteria or viruses have been found to contain proteins that make them resemble the cells of body tissues, including those of the nervous system. In MS, the immune system may be activated to attack both the invaders and the tissues they resemble.
III SYMPTOMS AND COURSE
The symptoms of MS are different for everyone and vary widely in severity and duration. Symptoms include weakness, tingling, numbness, fatigue, incoordination, balance and vision problems, tremors, muscle stiffness known as spasticity, slurred speech, depression, bowel or bladder problems, sexual dysfunction, problems with memory or reasoning, and partial or complete paralysis. Although MS can cause severe discomfort and disability, it does not usually shorten life span.
Often MS begins with a single subtle symptom, such as blurred vision or leg tingling. For many people with MS, symptoms come and go unpredictably, making it difficult to plan for the future. While some people experience a course that does not significantly alter their lifestyles, others experience severe symptoms that may rob them of physical and mental abilities, their livelihoods, and their independence. Because it can alter family routines and roles, MS affects everyone in the family.
There are four recognized patterns of MS. In the relapsing-remitting course, which affects most people with MS, a person experiences an attack of symptoms, which then completely or partially subside until the next attack. About half of those with this form of the disease will later develop secondary-progressive MS, which involves progressive worsening of symptoms and may also include occasional flare-ups followed by partial recoveries. Less common is primary-progressive MS, involving a steady worsening of disability from disease outset, such as painful muscle spasms, urinary incontinence, and possibly, eventually, paralysis. Another less common form is progressive-relapsing MS, which starts with a pattern of steadily worsening disability along with periodic flare-ups.
MRI CylinderA woman enters a magnetic resonance imaging (MRI) cylinder. MRI is a diagnostic technique that generates images of the internal body. It specializes in creating a thin-section image of any part of the body—especially the heart, veins, arteries, brain, and central nervous system—from any angle or direction. MRI scans of the brains of people with multiple sclerosis reveal characteristic patches, or lesions, indicating inflammation. The multiple areas of scarring, or sclerosis, give the disease its name.Corbis
MS can be difficult to diagnose, as no single laboratory test clearly identifies the disease. It is primarily diagnosed by reviewing a person’s medical history and giving a neurological exam that tests for abnormal reflexes, muscle weakness or poor coordination, alterations of sensation, damage to the optic nerve, and other signs of brain or spinal cord damage.
Several tests can help confirm the diagnosis. Magnetic resonance imaging (MRI) can reveal characteristic patches, or lesions, in the brain where inflammation is occurring or has occurred. The name multiple sclerosis comes from these lesions—multiple areas of scarring, or sclerosis, in the brain and spinal cord. To positively diagnose MS, doctors must find evidence of lesions that occurred at different points in time in at least two places in the central nervous system. Although most people with a definite diagnosis of MS have lesions revealed by MRI, the absence of lesions does not rule out the disease.
The evoked potential test determines how long it takes an electrical nerve impulse, such as that generated by a flashing light, to travel through nerve fibers to the brain. In people with MS, the signal may be slower because demyelination impairs message transmission to the brain. A spinal tap, or lumbar puncture, is sometimes used to examine the spinal fluid for elevated levels of certain immune-system proteins that are present in up to 90 percent of people with MS.
There is currently no cure for MS, but drugs are available that can slow the course of the disease. Synthetic forms of interferon (a natural immune chemical that regulates immune responses) reduce the frequency and severity of relapses and slow the accumulation of disability over time. Glatiramer acetate is a mixture of synthetic polymers that may serve as a decoy for the immune system, reducing its attacks on myelin. This, in turn, can reduce the frequency of relapses, which may slow the progress of the disease. It has become increasingly clear that early treatment is crucial to prevent or delay further damage to the nervous system.
There are also treatments for specific symptoms, including corticosteroids (often taken intravenously), that can shorten the duration of an MS attack. Several drugs can relieve spasticity, fatigue, and bladder problems. People with MS often find that nondrug treatments, such as regular exercise and adequate rest, can help them to maintain more active lives. Physical therapy and exercise can help strengthen weakened muscles and improve coordination. Occupational therapy can improve daily living skills by teaching people with MS how to function with reduced motility, and speech therapy can help with speaking and swallowing difficulties (see Speech and Speech Disorders: Speech Therapy).
Advances in treatment research are giving hope to those affected with MS, and their families. Current research focuses on ways to block natural inhibitors to myelin and nerve regeneration, on how to harness natural growth factors and replacement cells to protect or repair nervous system tissues destroyed in MS, and on seeking to understand and stop disease progression. Researchers also seek clues to genetic and environmental factors that may increase or decrease a person’s risk of developing MS. For example, some research studies suggest that vitamin D may help protect against MS. Vitamin D is thought to play a role in regulating the body’s immune response. Vitamin D is manufactured in the body, and levels of vitamin D can increase through exposure to sunlight. A protective effect from vitamin D could explain why the rate of MS increases with geographic distance from the equator, as exposure to sunlight decreases.
Stephen C. Reingold