AbstractThrombotic microangiopathy (TMA) is a syndrome characterized by thrombosis in capillaries and arterioles, resulting in microangiopathic hemolytic anemia, thrombocytopenia and target organ injury. In TMA presenting with severe hypertension, it is difficult to determine whether the TMA is primary and due to thrombotic thrombocytopenic purpura (TTP) or secondary to severe hypertension. The response to antihypertensive medication favors the diagnosis of severe hypertension as the cause of TMA. Comorbid inflammatory disease supports the diagnosis of TTP-induced TMA. This case describes a 75-year-old woman with Castleman disease who presented with severe hypertension and TMA. She improved with hypertension therapy. However, ADAMST13 showed zero activity, and the diagnosis was TTP. In cases of TMA accompanied by severe hypertension, it is challenging to diagnose the cause of TMA. Even when there is a pronounced clinical response to lowering blood pressure, the diagnosis of TTP should be considered, particularly when an inflammatory disease is present.