Thrombotic microangiopathy not associated with the classic/idiopathic TTP-HUS

Thrombotic microangiopathy (TMA) is characterized by the formation of platelet thrombi and vascular wall injury in the microcirculation associated with hallmark clinical features of acute thrombocytopenia, microangiopathic hemolytic anemia (MAHA), and visceral organ injury, especially involving the kidneys and brain. Of all TMA cases, a third of them are due to the classic TTP-HUS; the remaining two-thirds are nonclassic and considered as secondary TMA that occurs in a variety of clinical settings including in microangiopathic antiphospholipid syndrome (MAPS), systemic lupus erythematosus (SLE) and other connective tissue diseases, a wide range of systemic infections, pregnancy, drug ingestion, disseminated malignancy, solid organ transplantation, bone marrow and hematopoietic stem cell transplantations, and, rarely, with severe pancreatitis and surgery. This chapter focuses on entities of secondary TMA and reviews their pathogenesis, clinicopathological presentation, diagnosis, prognosis, and treatment strategy.