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Dermoscopy in facilitating the recognition of acrodermatitis continua of Hallopeau

Dear Editor, Acrodermatitis continua of Hallopeau (ACH) is a rare chronic dermatosis presenting as multiple sterile pustules on an erythematous base associated with scaling/hyperkeratosis typically involving the subungual/distal area of one or several fingers and/or toes. It is generally regarded as a variant of pustular psoriasis, although some authors classify this condition as a separate entity. Prompt recognition of ACH is of utmost importance as, if not correctly treated, it may lead to destructive sequelae, including nail loss and distal phalanx osteolysis. However, diagnosing ACH may be a difficult task, especially when pustules are too tiny or are masked by overlying hyperkeratosis/scaling, with consequent misdiagnoses and inadequate management. We report two instances of ACH to highlight for the first time the usefulness of dermoscopy as a supportive tool in recognizing such a condition. Two otherwise healthy patients, a 55-year-old man (case 1) and a 47-year-old woman (case 2), presented with bilateral fingernail dystrophy characterized by hyperkeratosis and partial nail plate loss (Fig. 1a,c), both of them previously being classified on clinical ground as onychomycosis and treated with oral antimycotic agents without any improvement after 2–3 months of therapy. In both cases, dermoscopic examination showed whitish-yellowish hyperkeratosis/scaling along with single or multiple pustules (Fig. 1b,d); moreover, dotted and linear vessels as well as hemorrhagic spots were also seen in case 1 (Fig. 1b). Fungal culture of scaling and bacterial culture of pustular fluid yielded negative results, consistent with the diagnosis of ACH. Both the patients were treated with oral acitretin (0.5 mg/kg daily) with remarkable improvement after a few weeks. Dermoscopy is increasingly used to assist the non-invasive diagnosis of many inflammatory skin/nail conditions by displaying findings which are hardly visible to the naked eye. In our ACH instances, dermoscopic assessment was very useful to highlight the typical pustules, which were not evident on clinical examination because of their small size and the overlying scaling/hyperkeratosis. Indeed, in addition to the magnification aid, polarized dermoscopy is notoriously able to bypass the superficial corneum layer, thus facilitating the view of the