Vasculitis occurs when your immune system mistakenly sees blood vessel cells as foreign. The immune system then attacks those cells as if they were an invader, such as a bacteria or virus. It's not always clear why this happens, but an infection, some cancers, certain immune system disorders or an allergic reaction may serve as the trigger.

Blood vessels affected by vasculitis become inflamed, which can cause the layers of the blood vessel wall to thicken. This narrows the blood vessels, reducing the amount of blood — and therefore oxygen and vital nutrients — that reaches your body's tissues. In some cases, a blood clot may form in an affected blood vessel, obstructing blood flow. Sometimes instead of becoming narrower, a blood vessel may weaken and form a bulge (aneurysm), a potentially life-threatening condition.

Vasculitis with no known cause (primary vasculitis)

For many of its forms, the cause of vasculitis is unknown. These forms of vasculitis are called primary vasculitis.

Vasculitis that occurs due to another disease (secondary vasculitis)

Forms of vasculitis for which an underlying disease is the cause are called secondary vasculitis. Examples of causes of secondary vasculitis include:

  • Infections. Some vasculitis occurs in response to an infection. For instance, most cases of cryoglobulinemia are the result of the hepatitis C virus infection, and the hepatitis B virus infection causes some cases of polyarteritis nodosa.
  • Immune system diseases. Vasculitis can also occur as the result of some diseases of the immune system, such as rheumatoid arthritis, lupus and scleroderma.
  • Allergic reactions. Sometimes an allergic reaction to a medication may cause vasculitis.
  • Blood cell cancers. Cancer that affects the blood cells, including leukemia and lymphoma, can cause vasculitis.
Oct. 08, 2011

You Are ... The Campaign for Mayo Clinic

Mayo Clinic is a not-for-profit organization. Make a difference today.