Multiple Sclerosis (MS) is a disease that affects your central nervous system, which includes your brain and spinal cord. It affects about 400,000 people in the United States. You can develop MS at any age, but it's usually diagnosed in people 20 to 40 years old. Women are twice as likely to be diagnosed with MS as men. You may be at higher risk if you are Caucasian, have a family history of MS or grew up in a northern climate. MS damages the coverings around nerves in your brain and spinal cord. This covering—called myelin—is like the covering around an electric wire. When myelin is damaged, nerve signals between your brain, spinal cord and body are slowed or interrupted. Over time, the damage may become permanent.

For most people with MS, symptoms tend to come and go. Symptoms may flare up for weeks or months and then go away. Symptoms are different for different people, but common symptoms include:

  • Vision changes
  • Tiredness and lack of energy (fatigue)
  • Thinking and memory problems
  • Muscle weakness
  • Tremor
  • Numbness or tingling sensations
  • Muscle stiffness or spasms
  • Clumsiness or balance problems, which may affect walking
  • Speech problems
  • Dizziness
  • Bowel or bladder function problems
  • Shock-like sensations in the neck or spine

Most people with MS do not become severely disabled. They have symptoms that come and go and their disease is helped by medications. When symptoms flare up and new symptoms develop, that's called a relapse. When symptoms go away, it's called a remission. However, a few people with MS have symptoms that stay and tend to get worse. They do not have remissions. These people may become more disabled.

MS occurs when the body’s defense system—the immune system—attacks myelin as if it were a foreign invader, like a virus or bacteria. The immune system sends proteins, called antibodies, and white blood cells to attack myelin. The attack causes inflammation, which may leave scar tissue behind. This type of attack is called an autoimmune disease.

Why some people develop MS and others don't is not known. The cause may be certain genes that increase your risk for MS. These genes may need to be triggered or activated by something in your environment. A viral infection is one possible trigger.

Types of Multiple Sclerosis

There are three main types of MS:

  • Primary-Progressive MS (PPMS): This type affects 10 to 20 percent of people with MS. People with this type of MS do not have flares of symptoms followed by improvement. Once symptoms start, they get gradually worse.
  • Relapsing-Remitting MS (RRMS): This is the most common type, affecting 65 to 80 percent of those with MS. People with this type experience flare-ups or relapses, and then symptoms decrease or go away completely. Remission can last years before symptoms return. Flare-ups and relapses are unpredictable but may be triggered by infection and fever.
  • Secondary-Progressive MS (SPMS): About half of those who have relapsing-remitting MS develop SPMS within 10 years. People with this type experience worsening of symptoms and more permanent symptoms. They may or may not have periods of remission.