Linear neutrophilic dermatitis: a seasonal outbreak of Paederus dermatitis in upper Egypt.

In this retrospective study, we investigated a mysterious acute linear eruption that was reported yearly in 300 Egyptian patients, with peaks in June and September, without a clear diagnosis. The lesions evolved suddenly in all patients and presented as an erythematous linear eruption with a grayish center and vesicles and/or pustules located in the middle of the plaques. Only areas that were not covered by clothing were affected. Microscopic examination of skin biopsies revealed striking neutrophilic spongiotic lacunae within a degenerated epidermis and moderate dermal infiltrate. After excluding other possible differential diagnoses associated with linear lesions, the Paederus beetle was concluded to be the initiator of this irritant dermatitis reaction. An outbreak of acute linear neutrophilic dermatitis may develop due to exposure to the Paederus beetle with no sex or age predilections.