A scanning microscopic clue to the diagnosis of arthropod assault reaction: alteration of interstitial tissue is more common than a wedge‐shaped inflammatory infiltrate

Background:  A scanning microscopic clue to the diagnosis of arthropod assault reactions is a wedge-shaped inflammatory infiltrate. However, to describe an inflammatory infiltrate as wedge-shaped or not involves a high degree of subjectivity. Methods:  We studied hematoxylin and eosin-stained sections of 137 biopsies of arthropod assault reactions for epidermal and dermal changes and for the composition, density and depth of the inflammatory infiltrate. Results:  We found a wedge-shaped inflammatory component in only 10.2% of the cases. A much more common feature is an alteration of the interstitial tissue present in 85.4% of the biopsies. It consisted of a narrowing of the spaces between the collagen bundles, which was readily observable on scanning magnification. On higher magnification, a loosely textured basophilic material was often noted within the dermis. Conclusions:  The hitherto often emphasized wedge-shaped configuration of the inflammatory component of arthropod assault reactions is not of great diagnostic value. The altered interstitial tissue is easily recognizable by its diminished interstitial spaces at low power magnification and can serve as a scanning magnification clue to the diagnosis of arthropod assault reactions.