What Is Multiple Sclerosis?

Heather and Jane are paid spokespersons for Biogen Idec, and these are their stories. Individual results may vary.

Multiple sclerosis (MS) is a chronic, progressive disease affecting about 400,000 people in the United States and more than 2.1 million people worldwide. Doctors call MS "chronic" because it never goes away, and "progressive," because it typically worsens over time.

MS affects your central nervous system (CNS), which includes your brain and spinal cord. Your CNS sends and receives signals to and from all parts of your body through nerve fibers. Most nerve fibers in your CNS are surrounded by a coating, called myelin, that helps nerve fibers transmit the signals they receive.

When you have MS, however, the myelin becomes inflamed and damaged. As a result, your CNS can no longer communicate with the rest of your body as effectively as before.

Doctors believe that the damage MS does to your myelin is the result of an autoimmune response. When your body has an autoimmune response, your immune system targets healthy parts of your body mistaking them for bacteria or other foreign substances.

This same autoimmune response also damages your blood-brain barrier. Normally, the blood-brain barrier, a wall of cells around the blood vessels in your CNS, protects your brain from bacteria and other harmful substances in your blood. When you have MS, holes appear in your blood-brain barrier. This allows harmful immune cells to cross into your CNS where they can cause inflammation and tissue damage, also known as lesions.

The Impact of MS on your CNS

In addition to causing lesions in your CNS, MS may also cause the brain and the spinal cord to shrink, a process known as atrophy. The exact relationship between lesions, shrinkage and the symptoms you may experience is still unknown.

How MS gets worse over time

MS can progress, or become worse, in two different ways: through flare-ups and through a process called silent activity.

Flare-ups

Flare-ups are the outward signs of active inflammation in your CNS. During a flare-up, you may develop new symptoms or your existing symptoms may get worse. Flare-ups may:

• Range from mild to severe
• Come on without warning
• Last for days, weeks, or months
• Cause permanent damage to your CNS
• Lead to future disability

On average, people who don't treat their MS have about one flare-up a year. What's more, some people have flare-ups more often than just once a year. That may not sound too scary, but even mild flare-ups can cause permanent damage to your CNS and contribute to future disability. That's why it's so important to start an MS treatment that can help reduce flare-ups.

Silent activity

Silent MS activity takes place with no outward symptoms. That makes it, in some ways, more dangerous than a flare-up, because it may cause damage you can't feel directly and can't report to your doctor. Types of damage include:

• Damage to the blood-brain barrier: Holes occur in the barrier that normally protects your brain from bacteria and other harmful substances in your blood
• Brain lesions: Injuries to your brain tissue
• Brain shrinkage: The loss of brain tissue

Safety and efficacy of treatment with AVONEX beyond three years is not known.

Talk with your doctor to find out if AVONEX is right for you.