87. 25-year-old female presented with a history of easy bruising for 3 months and extensive skin bleeding for 1 day. Physical examination was normal except extensive petechia and purpura all over her body. CBC: Hb 12.0 g/dL, MCV 79 fL, RDW 16.5 %, WBC 6.7x109/L, PMN 75%, L 20%, M 4%, E 1%, no abnormal cells, platelet 5.0x109/L. Anti-HIV was negative. The most likely diagnosis is *