Multiple sclerosis (MS) is a chronic condition that affects the central nervous system. This system includes the brain and spinal cord. It contains the nerves that control everything your body does, such as thinking, feeling, seeing, smelling, tasting, and moving. MS affects about 1 in 400 Canadians and usually appears between the ages of 20 and 49, although it may occur at any age.

Your nerves are covered by an intact protective layer known as the myelin sheath. This covering helps to speed electrical signals in the brain. With MS, researchers think that the myelin sheath somehow becomes inflamed and damaged in small patches. It is not known what chain of events starts this damage, but once the injury occurs, electrical signals in the brain are slowed down.

It is believed that MS is an autoimmune disease (a condition in which an individual's immune system starts reacting against his or her own tissues) and cannot be spread from person to person. For unknown reasons, the immune system sees the myelin sheath as foreign and attacks it.

There are 3 types of MS:

Relapsing-remitting MS is the most common form of MS, affecting 85% to 90% of people with the condition at onset. This type of MS is associated with "flare-ups" where symptoms worsen for weeks or months, and with remissions where symptoms completely or partially improve.

Primary-progressive MS affects 10% to 15% of people with MS and is associated with slow, but mostly continuous, worsening of the disease from the time of onset.

Secondary-progressive MS is associated with an initial period of relapsing-remitting disease followed by steady worsening and minor remissions. Approximately 65% of people with relapsing-remitting MS will develop this form of MS within 15 to 20 years.

The cause of MS is still unknown. However, most research suggests that an abnormal response by the immune system damages the myelin sheath.

Normally, the immune system protects and defends the body against foreign substances. But with autoimmune diseases, the body attacks its own tissue. Researchers don't know exactly what causes the immune system to do this, but they know that certain factors are involved, including:

• gender: Women are 2 to 3 times as likely as men to get the disease.
• family history of MS: A family history increases the risk of developing MS. The closer the relationship, the higher the risk. For example, if your identical twin develops the illness, your chances are about 30%. But research has shown that there is no single "MS gene." It will take many more years to understand the role that genetics play in MS.
• environmental factors: MS occurs most commonly in those living in northern climates, including anywhere north of Denver or Philadelphia in North America. MS is also common in Northern Europe and Japan. Where you spend your early life may play a role in your odds of developing MS. Tropical and southern regions may be considered low risk. If you moved from the south to a higher risk area in the north during your early life, you may still have a low risk for the disease. There is some early evidence that sunlight exposure and high levels of vitamin D may decrease the chance of developing MS. However, further research is required before supplements can be recommended for this purpose.
• infections: Researchers believe that many autoimmune diseases are provoked by some kind of infection that strikes people who have a certain genetic makeup. Many bacteria carry proteins that can mimic the cells of the body. This can trick your body's defences into attacking your own tissues, even after the infection has gone. Recently, researchers have been looking at viruses as possible triggers, especially those that cause chickenpox and herpes

MS is unpredictable and affects each person in a different way. People can experience different symptoms of varying severities during an attack.

The type of symptoms depends on the location of the damage. Symptoms commonly include:

• bladder problems, such as urinary incontinence
• bowel problems, such as constipation
• cognitive problems (e.g., memory loss)
• difficulty walking
• dizziness and sensations of spinning
• extreme tiredness
• headache
• hearing loss
• itching
• mental health problems (e.g., depression)
• muscle stiffness or spasms
• numbness and tingling
• pain
• seizures
• sexual problems, such as reduced sensation, decrease in sex drive, and problems maintaining an erection
• speech and swallowing problems
• shaking
• vision problems

Having one or more of these symptoms does not necessarily mean that you have MS, but you should see a doctor if you suspect that your symptoms might be related to MS.

If your doctor suspects MS, you will be referred to a neurologist for various tests. Neurological tests examine reflexes, eye movements, strength, sensation, and coordination. Your medical and family histories will also play an important role in the diagnosis.

Further tests might include:

• magnetic resonance imaging (MRI), a type of scan that takes pictures of your brain and spinal cord
• evoked potential, which measures nerve signals from your body to your brain; in MS, these signals are slower and weaker
• spinal fluid examination, which checks the spinal fluid for signs of MS

To confirm a diagnosis of MS, a person must have signs of disease in different parts of the nervous system and at least two separate flare-ups. However, if a person has suffered only a single attack of symptoms that could be MS, an MRI may be done to evaluate the chance of this progressing to MS. Early treatment of a single flare-up may prevent or delay further relapses.

Although no cure exists for MS, treatment aims to reduce the number of relapses or attacks, and to lessen their severity when they do occur. To accomplish this, medications are given by injection. High doses of steroids (given either intravenously or orally) are used to treat relapses.

Disease-modifying medications* such as teriflunomide, fingolimod, glatiramer, dimethyl fumarate, interferon beta-1a, interferon beta-1b, peginterferon beta 1a, alemtuzumab, daclizumab, ofatumumab, ocrelizumab, cladribine, siponimod, and natalizumab are used to reduce disease activity and progression.

A variety of other medications and lifestyle interventions may be used to help manage symptoms such as bladder or bowel problems, tiredness, pain, depression, anxiety, muscle spasms, sexual dysfunction, vision problems, difficulty walking, and stress, but these have no effect on the actual disease. Rehabilitation programs, including physical and occupational therapy, are an important part of helping people live with MS.

Other ways to reduce the burden of symptoms include:

• getting a yearly flu shot
• avoiding and minimizing stress
• avoiding heat, such as in whirlpools and hot showers
• exercising moderately
• doing muscle-stretching exercises

Research currently focuses on medications to counter the specific immune antibodies that attack myelin, on growth factors that can help replace myelin between attacks, and on experimental techniques such as bone marrow transplant and surgical procedures.