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INTRODUCTION

This chapter discusses disorders in which there is either a breach of, or injury to, the blood vessel wall. In many instances, depending on severity, damage to the vessels will lead to extravasation of cellular blood contents.

    Purpura is the extravasation of blood from vessels in the skin. It may have hematologic causes or hydrostatic causes, or may be related to vessel injury (Table 14.1). The latter may include physical damage (e.g. trauma), occlusion of vessels (e.g. prothrombotic or embolic disorders), or inflammation of the vessel walls (vasculitis). A useful concept in evaluating these possible causes in the skin is that inflammation (i.e. vasculitis) will produce local swelling as well as extravasation of erythrocytes, a combination termed palpable purpura and illustrated previously (Fig. 2.14).

    Vasculitis occurs in several situations. It may be primary, the main topic of this chapter, or it may be associated with the collagen vascular or connective tissue diseases, such as lupus erythematosus, scleroderma, and dermatomyositis, discussed in Chapter 13. Dermatologists are most commonly faced with a pattern known as cutaneous small-vessel vasculitis (Fig. 14.1); an approach to this pattern will be outlined later.

    Most primary vasculitides involve neutrophil polymorphs in at least some of their lesions. For this reason, neutrophilic dermatoses are also discussed here; they are often centered around vessels and may include a component of vessel wall inflammation, so there is a degree of pathologic overlap with vasculitis.

Figure 14.1 Cutaneous small-vessel vasculitis showing palpable purpuric lesions with necrosis and crusting. In this patient, very rarely, the trigger was extensive crusted scabies.

Table 14.1 CLASSIFICATION AND CAUSES OF PURPURA AND ECCHYMOSIS

Cause	Examples and comments
Platelet disorders Thrombocytopenia Abnormal platelet function   Thrombocytosis	Numerous causes Especially due to drugs, uremia, myeloproliferative disease, inherited forms Mainly myeloproliferative disorders or isolated (‘essential')
Coagulation disordersa Inherited Drugs Localized Metabolic Thrombophilias Disseminated intravascular coagulopathy and purpura fulminans	For example hemophilia For example anticoagulants For example heparin injection sites, some insect bites For example vitamin K deficiency, hepatic failure (decreased synthesis of clotting factors) For example protein C deficiency, protein S deficiency
Other intravascular causes of purpura Dysproteinemias syndrome Cryoproteinemias Emboli	Hypergammaglobulinemic purpura (Waldenström), Sjögren Crystal , fat, myxoma, infective
Non-thrombocytopenic vascular causes of purpura Raised intravascular pressure Decreased support Abnormal vasculature Non-thrombocytopenic toxin- and drug-induced purpura Purpura associated with infections Capillaritis (pigmented purpuric dermatoses) Vasculitis Associated with other dermatoses that are not usually purpuric	Coughing, vomiting, stasis Actinic (‘senile') purpura, corticosteroid purpura, scurvy, amyloidosis, Ehlers–Danlos syndrome For example purpura around vascular lesions
Other causes of purpura or ecchymosis Physical and artefactual causes Multifactorial purpura associated with systemic diseases Easy bruising syndrome and purpura simplex Paroxysmal finger hematoma (Achenbach syndrome) Painful bruising (autoerythrocyte sensitization, Gardner–Diamond) syndrome Stigmata

aUsually cause ecchymosis.

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White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.