Arthropod bite and analogous reaction

Early

Wedge shape of a perivascular and interstitial infiltrate
Lymphocytes and eosinophils around blood vessels with eosinophils scattered interstitial in the reticular dermis
Slight edema of the papillary dermis
A discrete focus of spongiosis sometimes present in the epidermis at the site of the "bite", i.e., directly above the apex of the wedge formed by inflammatory cells whose vertex within the dermis points to the subcutaneous fat.

Fully developed

Infiltrate of lymphocytes and eosinophils denser and deeper than in an early lesion; the subcutaneous fat my be involved
Edema of the papillary dermis more marked than in an early lesion
Spongiosis, sometimes in company with a multiloculated vesicle and epidermal necrosis, in a focus in the center of the lesion

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