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SUMMARY
Purpura, the clinical manifestation of blood extravasation into mucosa or skin, results from various conditions, including rheumatologic, infectious, dermatologic, traumatic, and hematologic disorders. This chapter does not detail purpura resulting from quantitative or functional defects in hemostasis and coagulation, such as deficiencies of platelets or coagulation factors; these causes are discussed in other chapters (e.g., thrombocytopenia in Chap. 117; coagulation factor deficiencies in Chaps. 123 and 124).
The differential diagnosis of the disparate causes of noncoagulopathic purpura is best approached by stratifying purpura into three types of lesions: (1) palpable or retiform and noninflammatory, such as hyperglobulinemic purpura of Waldenström; (2) palpable or nonpalpable but inflammatory, such as Henoch-Schönlein purpura; and (3) nonpalpable and noninflammatory, such as senile purpura. By accounting for palpability, presence of inflammation, size, and shape, the differential diagnosis of a particular lesion can be significantly reduced.
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Acronyms and Abbreviations
ANCA, antineutrophil cytoplasmic antibody; APS, antiphospholipid syndrome; CSS, Churg-Strauss syndrome; DIC, disseminated intravascular coagulation; HCV, hepatitis C virus; HHT, hereditary hemorrhagic telangiectasia; HP, hypergammaglobulinemic purpura; HSP, Henoch-Schönlein purpura; MELAS, mitochondrial encephalopathy, lactic acidosis, stroke-like; SLE, systemic lupus erythematosus; WG, Wegener granulomatosis.
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DEFINITION AND DIAGNOSTIC APPROACH
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Purpura refers to visible hemorrhage into mucous membranes or skin, which corresponds to extravasation of red blood cells around small dermal vessels and chronic hemosiderin deposition.1 Purpuric lesions, by definition, do not blanch completely upon compression, as opposed to erythema. Blanching is commonly tested by compression of skin lesions with a glass slide, referred to as diascopy (Fig. 122–1). Certain conditions give rise to lesions that mimic purpura with incomplete blanching upon diascopy, but are not purpura because no hemorrhage has occurred. Examples include disorders that impede on the red cell flow, such as tortuous veins.1
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Assessing lesion palpability is the first step in evaluating purpuric lesions (Fig. 122–2). The causes for palpability are varied and include fibrin deposition, localized edema, significant cellular infiltration, and subcutaneous extravasation of red blood cells.
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Inspecting the lesion for inflammatory changes is the next step in evaluating purpuric lesions. The presence of pain, erythema, and palpation for warmth and localized swelling are signs of inflammation and suggest a vasculitis or immune complex disorder.
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The shape of a purpuric lesion, either round or retiform (branching), is important in assessing the lesion. In the absence of accompanying inflammation, retiform purpuric lesions suggest small vessel occlusion. A retiform, inflammatory purpuric lesion supports the diagnosis of vasculitis as a result of immunoglobulin (Ig) complex formation.2 Small, ...