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Purpura, the clinical manifestation of red blood cell extravasation into mucosa or skin, results from various conditions, including rheumatologic, infectious, dermatologic, traumatic, and hematologic disorders. This chapter does not address purpura resulting from quantitative or functional deficiencies of platelets or coagulation factors; these causes are discussed in other chapters. The differential diagnosis of the disparate causes of nonthrombocytopenic 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.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: ANCA, antineutrophil cytoplasmic antibody; APS, antiphospholipid syndrome; CREST, calcinosis, Raynaud phenomenon, esophageal motor dysfunction, sclerodactyly, and telangiectasia; CSS, Churg-Strauss syndrome; DIC, disseminated intravascular coagulation; HCV, hepatitis C virus; HP, hypergammaglobulinemic purpura; HSP, Henoch-Schönlein purpura; MELAS, mitochondrial encephalopathy, lactic acidosis, stroke-like; SLE, systemic lupus erythematosus; WG, Wegener granulomatosis.

Purpura, from the Latin for purple, refers to visible hemorrhage into mucous membranes or skin, which corresponds to extravasation of red blood cells around dermal small 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. 123–1). 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

Figure 123–1.

A. Spider telangiectasia. B. Blanching of spider telangiectasia. Note that spider telangiectasia blanches with diascopy.

Assessing lesion palpability is the first step in evaluating purpuric lesions (Fig. 123–2). The causes for palpability are varied and include fibrin deposition, localized edema, significant cellular infiltration, and subcutaneous extravasation of red blood cells.

Figure 123–2.

Bedside approach to purpuric lesion diagnosis.

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.

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....

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