Mibelli revisited: a case of type 2 segmental porokeratosis from 1893.

In autosomal dominant skin disorders, a pronounced mosaic involvement may sometimes be found to be superimposed on the ordinary nonsegmental lesions. Such "type 2 segmental manifestation" reflects loss of heterozygosity occurring at an early developmental stage, giving rise to a cell clone that lacks the corresponding wild-type allele. Here, this genetic concept is applied to an unusual case of plaque-type porokeratosis of Mibelli (PM) as published in 1893 by Vittorio Mibelli in the International Atlas of Rare Skin Diseases. The right forearm and hand of the 21-year-old patient showed a pronounced linear porokeratosis that had developed since the age of 2 years. Moreover, nonsegmental lesions of PM involved both hands and forearms as well as the face and the neck, having first been noticed at the age of 7 years. Two siblings and the father were likewise affected with PM. Hence, Mibelli's case from 1893 meets all of the criteria of a type 2 segmental manifestation of an autosomal dominant skin disorder. Recognizing such cases of superimposed segmental involvement may help elucidate the molecular basis of PM.

Porokeratosis of Mibelli. Overview and review of the literature.

Porokeratosis of Mibelli is an uncommon dermatosis, which may be associated with immunosuppression and may undergo malignant transformation. Due to the wide range of clinical presentations, numerous classifications have evolved, resulting in some confusion. This article examines the classification and presentation of porokeratosis and, in particular, reviews the association with immunosuppression.