Immune-pathophysiology and -therapy of childhood purpura

Childhood purpura Overview Purpura (from the Latin, purpura, meaning "purple") is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin. Purpura measure 0.3-1cm, while petechiae measure less than 3mm and ecchymoses greater than 1cm. The integrity of the vascular system depends on three interacting elements: platelets, plasma coagulation factors and blood vessels. All three elements are required for proper hemostasis, but the pattern of bleeding depends to some extent on the specific defect. In general, platelet disorders manifest petechiae, mucosal bleeding (wet purpura) or, rarely, central nervous system bleeding; coagulation disorders present as ecchymoses or hemarthrosis; and vasculitic disorders present with palpable purpura. Purpura may be secondary to thrombocytopenia, platelet dysfunction, coagulation factor deficiency or vascular defect as shown in table 1. A thorough history (Table 2) and a careful physical examination (Table 3) are critical first steps in the evaluation of children with purpura. When the history and physical examination suggest the presence of a bleeding disorder, laboratory screening studies may include a complete blood count, peripheral blood smear, prothrombin time (PT) and activated partial thromboplastin time (aPTT). With few exceptions, these studies should identify most hemostatic defects (Figure 1).