New Eruption of Bullous Pemphigoid Within Disseminated Superficial Porokeratosis Lesions: A Rare Case Report

In 2024, a 75-year-old Chinese man presented with a complex dermatological case involving features of both disseminated superficial porokeratosis (DSP) and bullous pemphigoid (BP). The patient exhibited a long-standing history of pruritic annular brownish plaques with hyperkeratotic borders, alongside recent blistering eruptions on his hands, feet and trunk. Diagnostic investigations revealed distinct histopathological and immunological markers characteristic of both conditions. Treatment with intravenous methylprednisolone, topical corticosteroids and tretinoin cream led to rapid improvement of BP lesions but also DSP plaques, culminating in complete resolution without new eruptions during corticosteroid tapering. Dermoscopic examination unveiled unique features, including the 'double-track sign', dilated capillaries and a central yellowish translucent area with haemorrhagic crusts, underscoring the diagnostic utility of dermoscopy in elucidating this rare co-presentation. This case highlights the diagnostic challenges and therapeutic considerations in managing concurrent DSP and BP, shedding light on potential exacerbating factors and treatment outcomes deserving further exploration in dermatological research.