Causes Make an Appointment Refer a Patient Ask a Question Reviewed by the National Heart Lung and Blood Institute (August 01, 2009) Vasculitis is an inflammation of the blood vessels, but what causes the inflammation is often unknown. It is sometimes a side effect of the body's immune system response to a recent or chronic infection. It also can be a side effect of the body's response to a medicine. The body sometimes recognizes a medicine as a foreign substance, and may develop an "allergic reaction" to try to get rid of it. Symptoms Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.