Relapsing MS Glossary

Understanding more about relapsing MS

Common relapsing MS terms are defined here. To learn more about these terms, talk with your healthcare provider. Your healthcare provider is the best resource you have for learning more about your disease.

  • Autoimmune disease: When your immune system mistakes your own cells for a foreign invader and attacks them.
  • Blood-brain barrier: A wall of cells in the brain that prevents certain substances from entering.
  • Infusion:The process of flowing a solution into the body, usually through a vein.
  • Intravenous (IV): The passing of medicines into a vein through a needle attached to a tube.
  • Magnetic resonance imaging (MRI): A method of creating images of the inside of the body. MRI uses powerful magnets and radio waves to produce these images. Along with other devices, MRI may help confirm or determine a diagnosis. MRI can be particularly helpful when diagnosing disorders of the brain or spine because it can provide detailed pictures of certain regions of the body that are difficult to see using other types of scanning devices.
  • MRI brain lesions: Abnormal tissue in the brain detected by MRI.
  • Multiple sclerosis (MS): A disease that affects the brain and spinal cord. It is thought to be an autoimmune disease, and it is characterized by the demyelination, or destruction, of myelin sheath. Myelin sheath is the protective covering for the nerve fibers of the central nervous system, and it helps the nerve fibers transmit electrical impulses between different parts of the body. When myelin sheath is destroyed in MS, messages between different parts of the body are not transmitted as effectively. After the myelin is destroyed, scar tissue called sclerosis is left behind in the damaged areas, which are referred to as lesions or plaques. This damage to the nervous system can result in a myriad of symptoms, including vision problems and difficulty with muscle movement, coordination, and balance.
  • Myelin sheath: The thick, soft, white, fatty layer of protective material around nerve fibers. This material is called myelin. If the myelin sheath around nerve fibers deteriorates or is destroyed, it can interfere with the fibers' ability to transmit messages successfully from one part of the body to another.
  • Nerves: A bundle of nerve fibers that transmit messages between the nervous system and different parts of the body.
  • Physical disability progression: Total or partial loss of a person's bodily functions as measured by the Expanded Disability Status Scale (EDSS).
  • Relapse: When MS symptoms appear, reappear, or become worse. Also called a "flare-up," "attack," or "exacerbation."


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TYSABRI® (natalizumab) is a prescription medicine used to treat adults with relapsing forms of multiple sclerosis (MS) to slow the worsening of symptoms common in people with MS and to decrease the number of flare-ups (relapses). TYSABRI increases the risk of progressive multifocal leukoencephalopathy (PML). When starting and continuing treatment with TYSABRI, it is important to discuss with your doctor whether the expected benefit of TYSABRI is enough to outweigh this risk.

Important Safety Information

TYSABRI increases your risk of getting a rare brain infection—called progressive multifocal leukoencephalopathy (PML)—that usually leads to death or severe disability.

Before receiving TYSABRI, it is important to tell your doctor:
TYSABRI can cause serious side effects. If you have any of the symptoms listed below, call your doctor right away:
The most common side effects of TYSABRI are:
These are not all of the possible side effects of TYSABRI. For more information, ask your doctor. To report side effects to FDA, please call 1-800-FDA-1088.

Please see Full Prescribing Information (PDF) including Boxed Warning and Patient Medication Guide (PDF).

This information is not intended to replace discussions with your healthcare provider.