Clinical response in patients with idiopathic TTP and severe ADAMTS13 deficiency but without detectable inhibitor. Platelet count is shown in the top row and ADAMTS13 activity in bottom row as labeled. All data points of ADAMTS13 in each patient represented the means of 2 separate assays. The thick solid bar indicates daily plasma exchange (PEx); thick dashed bar, taper of plasma exchange; thin solid line, prednisone (P) administration; and thin dashed line, taper of prednisone. Other adjunctive therapies such as vincristine (V), splenectomy (S), and a combination of cyclophosphamide, vincristine and prednisone (CVP) are indicated with arrows in the top panel of the figure of each patient.