Vasculitis is a general term that refers to inflammation of blood vessels. Vasculitis can affect very small blood vessels (capillaries), medium-size blood vessels (arterioles and venules), or large blood vessels (arteries and veins). If blood flow in a vessel with vasculitis is reduced or stopped, the tissues that receive blood from that vessel begin to die.
Some of the many forms of vasculitis may be restricted to particular organs. Examples include vasculitis that affects only the skin, eye, brain, or certain internal organs. There are also types of vasculitis that may affect many organ systems at the same time. Some of these generalized forms may be quite mild and may not require treatment. Others may be severe, affecting critical organs.
In most cases, the cause of vasculitis is unknown; however, it is clear that the immune system (the system that keeps the body healthy) plays a role. While the immune system usually works to protect the body, it can sometimes become overactive, attacking parts of the body. Sometimes an allergic reaction to certain medicines can trigger the immune system to go awry. In other cases, the origins may be traced to recent or ongoing infections, such as those caused by certain viruses.
Vasculitis can be very serious. In an extreme situation, when a segment of a blood vessel becomes weakened, it may then stretch and bulge (called an aneurysm). The wall of the blood vessel can become so weak that it ruptures and bleeds, possibly causing death. Fortunately, this is a very rare event.
If a blood vessel becomes inflamed and narrowed, the blood supply to the area of the body it serves may be partially or completely blocked. If alternate blood vessels (called collateral blood vessels) are not available in sufficient quantity to carry the blood to such sites, the tissue supplied by the affected vessels will die. Because vasculitis can occur in any part of the body, any tissue or organ can be affected.