Petechial and purpuric rashes can cause even seasoned clinicians to become very concerned because they can signify dangerous disease such as meningococcemia, as well as more benign disorders such as viral infections. It is important for the pediatric hospitalist to have an approach to the evaluation and management of patients with petechiae or purpura. A more complete discussion of the individual disease entities associated with thrombocytopenia and coagulation disorders are provided in Chapters 9 and 92.

Petechiae and purpura are hemorrhages in skin or mucous membranes that are less than 2 mm in diameter or greater than 2 mm in diameter, respectively. These lesions do not blanch under diascopy. Ecchymoses are subcutaneous hemorrhages that are greater than 1 cm. Purpura fulminans is a progressive condition in which cutaneous infarctions occur and result in extensive skin necrosis.

Petechiae and purpura can occur from a variety of pathophysiologic mechanisms that interfere with the complex process of hemostasis. Platelets, von Willebrand factor, and the coagulation cascade are essential for hemostasis. Thrombocytopenia, abnormal platelet function, von Willebrand factor defects, and clotting factor deficits can result in petechiae and purpura. Disruption of normal vascular integrity, such as occurs with endothelial injury as a result of infection or inflammation, can cause petechiae and purpura. Mechanical causes, such as trauma or increased intravascular pressure from coughing or vomiting, can cause petechiae and purpura by this mechanism as well. Intrinsically abnormal vascular components, such as collagen defects in connective tissue disorders, can result in these lesions. Ecchymoses are most often caused by trauma. Purpura fulminans typically occurs in the setting of bacterial sepsis and disseminated intravascular coagulopathy (DIC).

Because a number of different pathophysiologic mechanisms can cause petechiae or purpura, the differential diagnosis is extensive (Table 34-1). The clinical manifestations of bleeding disorders vary according to the underlying defect. Thrombocytopenia and abnormal platelet function typically result in petechiae, ecchymoses, and persistent bleeding from superficial cuts and mucosal membranes. Infection and vasculitis can cause petechiae or purpura, which can be palpable. Clotting factor deficits and other coagulation disorders typically cause hemarthroses, soft tissue bleeding, and prolonged bleeding, but they can also cause petechiae or purpura. Von Willebrand disease is usually manifested as mucosal membrane bleeding, postsurgical bleeding, and menorrhagia, but it can result in petechiae. Disorders of vascular fragility can give rise to ecchymoses, as well as petechiae and purpura.