Vasculitis occurs if your immune system attacks your blood vessels by mistake. What causes this to happen isn't fully known.
A recent or chronic (ongoing) infection may prompt the attack. Your body also may attack its own blood vessels in reaction to a medicine.
Sometimes an autoimmune disorder triggers vasculitis. Autoimmune disorders occur if the immune system makes antibodies (proteins) that attack and damage the body's own tissues or cells. Examples of these disorders include lupus, rheumatoid arthritis, and scleroderma. You can have these disorders for years before developing vasculitis.
Vasculitis also may be linked to certain blood cancers, such as leukemia and lymphoma.