Vasculitis is a condition that involves inflammation in the blood vessels. The condition occurs if your immune system attacks your blood vessels by mistake. This may happen as the result of an infection, a medicine, or another disease or condition.
Vasculitis can affect any of the body’s blood vessels. These include arteries, veins, and capillaries. Arteries carry blood from your heart to your body’s organs. Veins carry blood from your organs and limbs back to your heart. Capillaries connect the small arteries and veins.
Source: NIH.gov
