Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease that causes a fall in the number of platelets. Platelets are small cells in the blood that help to form a clot when there is bleeding. Patients with ITP often have pinpoint-sized pinkish-purple spots (petechiae) or bruising of the skin, as well as nosebleeds, bleeding from the gums, and heavy menstrual periods.