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Skin-nontumor

Granulomatous but non-infectious disorders

Arthropod bites

Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC (see Reviewers page)
Revised: 25 August 2011, last major update June 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Definition
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● Small clusters of erythematous papules or large, deep, indurated, violaceous nodules resembling lymphoma
● Careful inspection will often reveal a punctum at the site where insect mouth parts entered the skin

Micro description
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● Inflammatory and granulomatous reactions with dense superficial and deep lymphocytes, eosinophils and plasma cells
● Variable parakeratosis, spongiosis, acanthosis and epidermal erosion
● May have lymphoid germinal centers resembling lymphoma, with destruction of adnexae and atypia
● Typically has wedge shaped polymorphic inflammatory infiltrate composed of lymphocytes, histiocytes, eosinophils and sometimes neutrophils
● Mouth parts may be identified in the center of the lesion; particularly in tick bites
● May have secondary vasculitis

Micro images
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Various images

Positive stains
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● CD30 (focal, may involve atypical cells, Am J Surg Pathol. 2003;27:912)

Differential diagnosis
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● Hypersensitivity reaction: no wedge shaped infiltrate
● Lymphomatoid papulosis: atypical lymphocytes
● Well's syndrome: eosinophilic cellulitis of unknown etiology

End of Skin-nontumor > Granulomatous but non-infectious disorders > Arthropod bites

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