Immune thrombocytopenia (previously called idiopathic thrombocytopenia purpura) is the less scary and usually not life threatening little sister of thrombotic thrombocytopenic purpura. It is an immune mediated consumptive thrombocytopenia and typically a diagnosis of exclusion.
Mechanism
Production of autoantibodies to platelet components, usually the IIIa complex, is the primary accepted mechanism for ITP. However, it must be said that the pathogenesis is poorly understood.
Primary ITP
Thrombocytopenia (count <100e9/L) in the absence of any underlying cause. There is little research and the author has never been faced with the need to know about it. Call a haematologist, they might know.
Secondary ITP
Thrombocytopenia in the context of a proceeding or intercurrent illness, without some kind of other consumptive pathology like DIC, is usually a result of antibody crossreactivity causing (mostly) splenic platelet clearance.