[Verrucous variant of porokeratosis of Mibelli as a differential diagnosis of psoriasis vulgaris].

In a 37-year-old man, diagnosis of verrucous porokeratosis could only be made by histological examination. Previously, the skin lesions on the right buttock had been treated by several dermatologists as psoriasis vulgaris. The clinical picture of both dermatoses was characterized by sharply defined, erythematous papules and plaques. Precise evaluation of the clinical morphology was key for diagnosis. Moreover, in contrast to psoriasis, verrucous porokeratosis is characterized by a high degree of treatment resistance.