ORIGINAL ARTICLE Paederus dermatitis in Egypt: a clinicopathological and ultrastructural study M Assaf, † E Nofal, ‡, * A Nofal, ‡ O Assar, ‡ A Azmy § † Pathology, ‡ Dermatology and § Histology Departments, Faculty of Medicine, Zagazig University, Zagazig, Egypt *Correspondence: A Nofal. E-mail: ahmadnofal5@hotmail.com Abstract 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. Received: 2 November 2009; Accepted: 21 January 2010 Keywords Clinicopathological and ultrastructural study, paederus dermatitis, pederin toxin Conflicts of interest None declared. Introduction Paederus dermatitis (PD) is a peculiar type of irritant contact dermatitis caused by contact with the vesicant chemical pederin contained in the body fluids of beetles of the genus Paederus that belongs to the family Staphylinidae. The other two major families of blister beetles are Meloidae and Oedemeridae. They contain the vesicant chemical cantharidin that causes a much less severe inflammatory reaction than that caused by pederin. 1 Paederus beetles neither bite nor sting, but when crushed against the skin or the eye, they cause irritation and blistering. Paederus dermatitis is characterized by vesicles and pustules on an erythematous base with sudden onset of stinging or burning sensation. The lesions usually appear on the exposed parts of the body, frequently have a linear configuration and usually heal within 2 weeks with hyperpigmentation. 2 In Egypt, after the sudden flood of the Nile River in 1994, an insect identified as Paederus alfierii attacked a factory beside maize field in Tanta city and all factory workers suffered from contact dermatitis. 3 Since then, seasonal outbreaks of PD have been observed in Egypt. 4 The aim of this study was to describe the clinical presentations of PD in East Delta governorates, Egypt, and to analyse the effect of pederin toxin on the skin by studying the histopathological and ultrastructural changes in some representative cases. Patients and methods The study included 113 patients with clinically diagnosed PD who came to the dermatology outpatient clinics of Zagazig University Hospitals, Egypt, between May 2007 and December 2008. Baseline characteristics of the patients including age, gender, place of resi- dence, use of fluorescent lighting at home, history of contact with ª 2010 The Authors JEADV 2010, 24, 1197–1201 Journal of the European Academy of Dermatology and Venereology ª 2010 European Academy of Dermatology and Venereology DOI: 10.1111/j.1468-3083.2010.03621.x JEADV