Diamond necklace appearance on ultraviolet fluorescence dermoscopy in porokeratosis

A 59-year-old man presented with multiple asymptomatic annular lesions over both legs of 2 years’ duration. Cutaneous examination revealed well-defined annular plaques with raised keratotic borders and relative central clearing, distributed symmetrically over the anterior aspects of the legs (Figure 1). Histopathological examination demonstrated a cornoid lamella, confirming the diagnosis of porokeratosis. Porokeratosis is a disorder of keratinization characterized clinically by annular lesions with a distinctive peripheral ridge.1 On dermoscopy, this ridge appears as a white peripheral border, often double-marginated, corresponding to the cornoid lamella and referred to as the keratin rim. This feature is regarded as a specific dermoscopic clue for porokeratosis but may not always be easily appreciable on routine dermoscopy. In the present case, ultraviolet-induced fluorescence dermoscopy enhanced visualization of the keratin rim, revealing a prominent blue-white annular ring at the lesion periphery, producing a characteristic ‘diamond necklace’ appearance (Figure 2). This pattern highlights the abnormal keratinization at the advancing edge of the lesion and allows improved noninvasive delineation of the cornoid lamella.2 Ultraviolet fluorescence dermoscopy may therefore serve as a useful adjunctive tool in the evaluation of porokeratosis.