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INTRODUCTION

When approaching a skin biopsy showing a dermal inflammatory cell infiltrate, one must take note of the presence and type of epidermal alteration, vascular changes, stromal response, and the character of the infiltrate itself. With respect to the former, the presence or absence of parakeratosis and orthohyperkeratosis and concomitant acanthosis or atrophy is a clue to the chronicity of the process and the type of injury pattern (eg, a spongiotic versus a cell-poor vacuolopathic interface dermatitis points, respectively, toward a delayed-type hypersensitivity reaction versus a humorally mediated or autoimmune disease). The infiltrate may be lymphohistiocytic or may contain an admixture of granulocytes, the former usually a sign of delayed-type hypersensitivity and the latter often a clue to an immune-complex (type III) or an anaphylactic (type I) hypersensitivity reaction. Histiocyte-predominant infiltrates may be a clue to a drug, viral, or idiopathic granulomatous process. The disposition of the infiltrate, either tightly “cuffed” around the vasculature or in both a perivascular and interstitial distribution, may be a clue to a gyrate erythema on one hand or to urticaria on the other. The stromal response, in the context of either a fibrosing reaction or collagen necrobiosis, may be a clue to a chronic process or a systemic disease. The presence or absence of vascular fibrin deposition is essential to the definition of vasculitis, and the presence or absence of endothelial cell necrosis, telangiectasia, and diminished vascular density of the superficial plexus, features indicative of certain connective tissue diseases, must be addressed, as must the type of inflammatory cells in vessel walls and lumina. Although by no means comprehensive, Table 5-1 provides a differential diagnostic approach to the superficial and the superficial and deep perivascular dermatitides. The reader is referred to other sections of this book for an in-depth consideration of many of these entities.

TABLE 5-1Perivascular Inflammatory Cell Infiltrates with Minimal or No Epidermal Alteration

URTICARIA

Clinical Features

The urticarias are common, transient eruptions that affect roughly 15% of the population at some time in life.1 They comprise palpable erythematous papules or wheals that lack surface alteration and wax and wane without a clinical residuum (Fig. 5-1A).

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