Actinic keratosis. Or maybe not?

Abstract

A 76-year-old white man presented with a 3-year history of an asymptomatic, ill-defined erythematous patch over his right temple (Fig. 1). A diagnostic biopsy had been taken from the same area 2 years previously, and had shown epidermal dysplasia in keeping with mildly dysplastic actinic keratosis (AK). Treatment with photodynamic therapy (PDT), cryotherapy, fluorouracil 5% cream, two successive courses of imiquimod 5% cream and a course of betamethasone valerate ointment had failed to provide improvement. The patch had cleared after a short course of oral steroids that had been prescribed for ulcerative colitis, but had recurred following cessation. The patient was on no regular medications, and there was no history of other topical treatment application or irradiation of the affected skin.Physical examination revealed a patch of erythema with central crusting, measuring 50 9 50 mm. The rest of the skin was clear, with no mucosal involvement. Laboratory investigations showed normal full blood count, while testing for antinuclear antibody was negative, as were bacterial skin swabs. Histopathological findingsA diagnostic biopsy was taken, and histological examination showed superficial acantholysis of the granular layer with a split at the granular-corneal layer interface, containing acantholytic cells and numerous polymorphs and leucocytes (Fig. 2). Direct immunofluorescence revealed epidermal intercellular staining with IgG ( Fig. 3) and C3. Re-evaluation of the initial skin biopsy showed features of AK with additional focal superficial acantholysis of the granular layer keratinocytes. ELISA revealed a weakly positive desmoglein (DSG)1 level of 46 and negative DSG3 level.What is your diagnosis? Figure 1 Ill-defined erythematous patch with central crusting on the right temple.Correspondence: Dr Dawn M. Caruana, Allen Lyle Centre for Dermatology, Western Infirmary Hospital, Dunbarton Road, Glasgow, G11-6NT, UK E-mail: dawn.caruana@gmail.com Conflict of interest: the authors declare that they have no conflicts of interest. Accepted for publication 6 October 2016Figure 2 Superficial acantholysis of the granular layer with a split at the granular-corneal layer interface containing acantholytic cells and numerous polymorphs and leucocytes (haematoxylin and eosin, original magnification 9100).ª