Quiz # 216
(1) The lesions pictured here developed after the patient had been “stung” by a wasp. They represent what is presumed to be a hypersensitivity reaction to materials injected into the skin by the arthropod, those lesions being known confusingly as “papular urticaria.” Clinically, they are urticarial papules, but are not real urtica, and histopathologically they are nearly indistinguishable from a lesion brought into being by a “bite,” directly, of an insect. Clinically, lesions of papular urticaria are not decorated in their center by a purpuric punctum (which is found often in urticarial papules brought into being by a “bite” directly) and histopathologically the infiltrate is without a wedge shape (which is found often in urticarial papules brought into being by a “bite” directly).
(2) Unlike true urtica, a lesion of papular urticaria, as it presents itself clinically, does not display pseudopods and lasts for much longer than a true wheal. In brief, so-called papular urticaria is not a true hive, but is hive-like.
(3) As a rule, findings histopathologic in the very center of a lesion that represents the actual site of the “bite” of an insect are a wedge-shaped, perivascular and interstitial infiltrate made up entirely of lymphocytes and eosinophils, both of those types of inflammatory cells being present around venules, whereas eosinophils almost exclusively are strewn in the interstitium. In a lesion of papular urticaria, which is not a response to a “direct hit” by an arthropod, the infiltrate does not assume the shape of a wedge. In this lesion of papular urticaria, neutrophils are notable, too. In short, in papular urticaria, on occasion, lymphocytes and eosinophils may be joined by neutrophils in variable number, as is the situation here.