Vasculitis is inflammation of blood vessels. In individuals 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 (ischemia), potentially resulting in pain, tissue damage, and, in some cases, malfunction of certain affected organs. Vasculitis may affect veins and arteries of any type or size; may involve a single organ or many organs and tissues of the body; and may be a primary disease process or occur due to or in association with a number of different underlying disorders. Therefore, the range and severity of symptoms and findings associated with vasculitis may vary greatly. The specific underlying 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.