A histopathologic study of arthropod bite reactions in 20 patients highlights relevant adnexal involvement

Insect bites produce diverse skin reactions. Although quite common, the histopathologic features of arthropod assaults have not ever been studied systemically.

Twenty biopsies from cases, clinically diagnosed as arthropod bite reactions between January 2003 and June 2007 were reviewed retrospectively. The aim of the study was to verify as to whether reliable histopathologic criteria could be established based on the frequency of findings observed.

Epidermal spongiosis (present in 16 of 20 cases), in particular spongiosis of the infundibular epithelium and acrosyringia as well as eosinophilic spongiosis, emerge as relevant diagnostic clues. A moderately dense, superficial and deep infiltrate consisting mainly of lymphocytes and eosinophils was prevalent in the dermis, with eosinophils tending to interstitial and periadnexal distribution. Of note, 19 of 20 (95%) cases revealed periadnexal involvement, whereas 16 of 20 (80%) had the infiltrate extending particularly along the sweat ducts and the coiled glands. In three biopsies, concomitant involvement of sweat glands, hair follicles and sebaceous glands was noted.

A practical histopathologic algorithm of arthropod bite recognition is proposed. The involvement of the sweat glands in the pattern of arthropod bite reaction is suggested as a new reliable diagnostic clue.