患者,男性,8歲,上呼吸道感染后出理全身皮膚黏膜廣泛出血點,伴牙齦出血.查血常規(guī):WBC4.2×109/L,Hb115g/L,PLT12×109/L,PAIgG118.6ng/107血小板,骨髓象示巨核細(xì)胞增多,但有成熟障礙。經(jīng)激素治療5天后,復(fù)查血小板89×109/L,PAIgG81.2ng/107血小板。該患者的診斷是()