Paederus fuscipes dermatitis. A histopathological study.

Paederus fuscipes (PF) dermatitis is a self-healing blistering disorder of the skin caused by a small insect belonging to genus Paederus, family Staphylinidae, order Coleoptera. Crushing PF on the skin causes acute dermatitis within 24 hours, corresponding in shape and dimensions to the area affected by the substance released (pederin). The acute vesicular lesions become crusted and scaly within a few days and heal completely in 10-12 days, with a transitory postinflammatory hypercromic patch. Twenty consecutive cases of PF dermatitis at different stages were studied histologically by routine light microscopy. The pederin causes a spectrum of histopathologic changes ranging from acute epidermal necrosis and blistering in acute stages, to marked acanthosis with mitotic figures in the late stages. PF dermatitis is an entomological model of irritant contact dermatitis, having histopathologic features of intraepidermal and subepidermal blistering, epidermal necrosis and acantholysis. The presence of some acantholytic foci, relatively far from the foci of clinically involved skin, in four of the cases considered suggests a possible role of pederin in inducing acantholysis indirectly. Acantholysis is probably caused by the release of epidermal proteases.