Paederus dermatitis in Egypt: a clinicopathological and ultrastructural study

Background Outbreaks of paederus dermatitis (PD) have been observed in different parts of the world, yet the histopathological and ultrastructural changes and their relationship to pederin toxin have not been described. Objective To describe the clinical presentations of PD in Egypt and to study the effects of pederin toxin on the skin by evaluating the histopathological and ultrastructural changes of some representative cases. Methods One hundred and thirteen patients with PD were studied clinically and epidemiologically. Skin biopsies were taken from 40 patients for histopathological examination and from 20 patients for electron microscopic (EM) examination. Results Clinically, the most common presentation comprised erythematous plaques with micropustules. Blisters exhibited a linear configuration in 40\% of the patients and kissing lesions were observed in 13\%. Multiple lesions occurred in 78\% of the patients and the face was the most commonly involved site (48\%). The insect was identified as Paederus alfierii. Histopathological examination revealed features of acute irritant dermatitis in the upper epidermis. Mitotic figures and apoptotic changes such as chromatin condensation and DNA fragmentation were identified in the basal and suprabasal layers. These features were confirmed by EM. Conclusions Clinical, histopathological and, for the first time, ultrastructural characteristics of paederus dermatitis are described. The pathological abnormalities of the upper epidermis are caused by the irritant effect of pederin toxin. The presence of apoptosis within the lower epidermis can be related to this toxin, a point that needs further research, hoping for its future implications in the management of hyperproliferative disorders.