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What Is Multiple Sclerosis?

Multiple sclerosis (MS) is a lifelong disease that affects your central nervous system (CNS), which is made up of your brain and spinal cord. MS is thought to be an autoimmune disease, a type of condition that causes the immune system to work against the body and attack healthy cells or tissue. In MS, immune cells, which may be triggered in the blood, attack the CNS. The resulting symptoms range in type and severity.

MS affects over 2 million people across the globe, and is about 2-3 times more common in women than in men. An MS diagnosis generally occurs between 20 and 50 years of age, but can happen in those younger or older. In fact, MS is the leading cause of neurological disability in young adults.

The course of MS is different for each person, but there are four disease types that usually occur: Relapsing-Remitting, Primary-Progressive, Secondary-Progressive, and Progressive-Relapsing.

Relapsing-Remitting Multiple Sclerosis

Relapsing-remitting MS (also called relapsing MS) accounts for around 85% of initial MS diagnoses. Flare-ups, or relapses, are visible signs of inflammation in the CNS. They are followed by periods of remission, which could result in complete or near-complete recovery.

AVONEX® (interferon beta-1a) is approved by the FDA to treat relapsing forms of MS, decreasing the number of flare-ups and slowing the occurrence of physical disability common in people with MS. AVONEX is approved for use in people who have experienced a first attack and have lesions consistent with MS on their MRI.

How Does MS Affect the Body?

While it's unclear exactly how MS causes CNS damage, doctors believe immune cells enter into the CNS and injure tissue. It's thought that when the immune system attacks the CNS, it damages the nerve fiber coating, called myelin, and creates scar tissue or sclerosis (which is how MS got its name).

The nerve fibers, or axons, that make up your CNS send and receive messages to all parts of your body. Myelin typically surrounds axons, adding protection and promoting effective signaling.

The damage to the axons interferes with communications between the CNS and the rest of the body. Because damage to the CNS communication system affects the entire body, symptoms of MS can range from general, such as fatigue, to specific, such as optic neuritis.

Relapsing MS & Disease Progression

Both flare-ups and silent progression can cause relapsing MS to worsen.


Flare-ups are the most noticeable and unpredictable reminders of relapsing MS. During a flare-up, also known as an exacerbation, attack, or relapse, existing MS symptoms worsen or new symptoms may appear. It's believed flare-ups are visible signs of inflammation in the CNS as the immune system attacks CNS cells. Each flare-up can occur without warning.

A flare-up is defined as lasting at least 24 hours and occurring at least 30 days after a previous flare-up. But flare-ups may vary in severity and can last from a few days to several months. On average, people who don't treat their relapsing MS have about one flare-up per year. While that may not sound like a lot, even infrequent or mild flare-ups can cause permanent damage to your CNS and may lead to future disability.

Silent Progression & Lesions

Even with no symptoms or visible signs, relapsing MS can advance within the CNS. Your neurologist may monitor disease progression using magnetic resonance imaging (MRI) scans. What they're looking for are lesions, or scar tissue, in your CNS. Some common types of lesions that can be studied with MRIs are T1 lesions with gadolinium enhancement (Gd+) and T2 lesions.

  • T1 lesions with Gd+ enhancements: Gd+ is a substance that helps your neurologist identify lesions using MRI. T1 lesions are typically thought to be new areas of active inflammation within the CNS.
  • T2 lesions: T2-weighted MRIs show the overall number of lesions (lesion load), which can include recent lesion development as well as previous damage.

The link between lesions and physical disability is not well understood.


Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Please see the full Prescribing Information and Medication Guide for additional important safety information. This information is not intended to replace discussions with your healthcare provider.


Kelly: Why I choose AVONEX


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