Purpura and Disorders of Microvascular Occlusion

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Purpura and Disorders of Microvascular Occlusion

• Purpura represents visible hemorrhage into the skin or mucous membranes; as a result and in contrast to erythema due to vasodilation, it is nonblanching upon application of external pressure.

• Purpura can be primary, where hemorrhage is an integral part of lesion formation, or secondary, where there is hemorrhage into established lesions due to factors such as venous hypertension, gravity, or thrombocytopenia.

• As purpuric lesions fade, their color evolves from red-purple or blue to brown or yellow-green.

• Primary purpura has a broad differential diagnosis, and it is helpful to categorize purpuric lesions based on their size and morphology.

– Petechiae: ≤3 mm and macular (Table 18.1; Fig. 18.1A).

Table 18.1

Causes of petechiae and ecchymosis with minor trauma.

DIC, disseminated intravascular coagulation; ITP, idiopathic thrombocytopenia purpura; TTP, thrombotic thrombocytopenic purpura.

Fig. 18.1 Clinical examples of petechiae and purpura. A Round to oval petechiae, ≤3 mm in diameter. B Actinic (solar) purpura and pseudoscars, both in sites of actinic damage plus trauma. C Non-inflammatory (bland) retiform purpura as well as hemorrhagic bullae in a patient with disseminated intravascular coagulation (DIC). D Palpable purpura due to cutaneous small vessel vasculitis (inflammation plus hemorrhage). A, Courtesy, Warren Piette, MD; B, Courtesy, Jean L. Bolognia, MD; C, Courtesy, Judit Stenn, MD.

– Ecchymoses: usually >1 cm and macular with round/oval to slightly irregular borders, and typically have an element of trauma in their pathogenesis (see Table 18.1; Fig. 18.1B); a greater volume of hemorrhage leads to a hematoma, which is palpable.

– Retiform purpura: reticulated, branching or stellate morphology, which reflects occlusion of the vessels that produce the livedo reticularis pattern (see Chapter 87; Tables 18.2 and 18.3; Figs. 18.1C and 18.2–18.9).

Table 18.2

Causes of retiform purpura.

^* Less common with low-molecular-weight heparin (≤1%) than unfractionated heparin; a transient decrease in the platelet count can also occur within the first 2 days of heparin therapy due to its direct effects on platelet activation.

^† May be an incidental finding in hospitalized patients; cold agglutinins rarely lead to acrocyanosis or purpura.

^** Skin lesions associated with subacute endocarditis are more likely to be inflammatory due to immune complex deposition, e.g. Osler’s nodes (tender red-purple papules), rather than Janeway lesions (purpuric macules; more common in acute endocarditis) on the hands and feet.

^‡ Cutaneous microthrombi and superficial thrombophlebitis have also been described.

Ab, antibody; PIGA, phosphatidylinositol glycan anchor class A; vWF, von Willebrand factor.

Table 18.3