Severe Acrodermatitis Continua of Hallopeau With Atypical Dermoscopic Features: A Diagnostic Pitfall.

Acrodermatitis continua of Hallopeau is a rare, chronic, relapsing form of localized pustular psoriasis characterized by painful sterile pustules and progressive destruction of the nail apparatus. Its clinical and dermoscopic features may be atypical, leading to diagnostic delays and inappropriate treatment. We present the case of a 78-year-old man with a one-year history of painful hyperkeratotic lesions affecting several fingers, with recent worsening, extension, and purulent discharge. Examination revealed bilateral chronic paronychia with peripheral erosions involving both thumbs and the left index finger, covered by thick yellow-green hyperkeratosis and purulent discharge. Proximal erythematous, crusted plaques extended to the digit bases. Chronic fungal paronychia with secondary bacterial infection was initially suspected. Bacterial and fungal cultures from purulent discharge and erosive areas were negative, although Pseudomonas aeruginosa was isolated from the extracted hyperkeratotic material. Following local care and antimicrobial therapy, the hyperkeratosis cleared, revealing anonychia and a markedly inflamed, erosive periungual surface. Dermoscopy showed large structureless whitish areas corresponding to giant pustules, coalescent milky pustules, yellowish crusts, whitish scales, and regularly distributed dotted, globular, and glomerular vessels. Shiny reticular white structures and small polymorphous white-yellow structures were also observed, mimicking nail erosive lichen planus and candidiasis. Histopathology demonstrated psoriasiform acanthosis, laminated parakeratosis, Munro microabscesses, dilated papillary dermal capillaries, and a neutrophilic and lymphohistiocytic infiltrate without interface changes, confirming acrodermatitis continua of Hallopeau with secondary bacterial superinfection. Acrodermatitis continua of Hallopeau should be considered in the differential diagnosis of chronic, destructive paronychia, particularly when accompanied by nail dystrophy or anonychia. Massive hyperkeratosis and atypical dermoscopic findings may obscure the diagnosis and mimic other inflammatory or infectious disorders. Accurate diagnosis requires integration of clinical, dermoscopic, microbiologic, and histopathologic findings to enable timely and appropriate management.