[Acquired thrombotic thrombocytopenic purpura with a smoldering clinical course].

Acquired thrombotic thrombocytopenic purpura (aTTP) is caused by a deficiency of ADAMTS13 activity due to neutralizing auto-autoantibodies (inhibitors) against ADAMTS13. Patients with aTTP show a rapid and fatal clinical course, unless an effective therapeutic intervention such as plasma exchange therapy (PEX) is performed. There is, however, a small population of patients who show a smoldering clinical course, for which no effective treatment strategy has yet been established. We herein report a 77-year-old man, who had repeated episodes of cerebral infarction and persistent thrombocytopenia over several months, but was not correctly diagnosed as having aTTP at a local hospital. However, sudden progression to an unconsciousness state together with thrombocytopenia prompted his physician to make a clinical diagnosis of aTTP, and the patient was then referred to our hospital, where the diagnosis of aTTP was confirmed by analyzing ADAMTS13. An improvement of his clinical signs was achieved with PEX and steroid therapy, but the latter had to be discontinued due to the development of grade 3 liver dysfunction. Despite discontinuation of steroid therapy, his clinical condition remained stable, but with a persistently low level of ADAMTS13 activity associated with the presence of low-titer inhibitors. Our experience may raise awareness of the diagnosis and treatment of aTTP with a smoldering clinical course.