Vasculitis is inflammation of blood vessels. In people with vasculitis, inflammation damages the lining of affected blood vessels, causing narrowing, the formation of blood clots (thrombosis), and/or blockage. As a result, there may be restriction of oxygenated blood supply to certain tissues, potentially resulting in pain, tissue damage, and, in some cases, malfunction of certain affected organs. The specific cause of vasculitis is not fully understood. However, in most cases, it is thought to be due to disturbances of the body's immune system. Follow the links below to find WebMD's comprehensive coverage about vasculitis, what it looks like, how to treat it, and much more.