Polyarteritis nodosa is an autoimmune disease. Your immune system is your body’s defense system. It fights diseases and infections. An autoimmune disease is a condition in which your body's immune system mistakenly attacks your own body. With polyarteritis nodosa, medium-sized arteries and, less commonly, small arteries become inflamed and damaged. The inflammation of the arteries affects many different organs.

The cause of polyarteritis nodosa is unknown. In relatively rare cases, however, it occurs with hepatitis B virus infection or hairy cell leukemia.