Other disorders of keratinization
Porokeratoses are chronic keratoatrophodermas of different clinical forms histologically characterized by columns of porokeratosis termed cornoid lamellae.
Porokeratosis of Mibelli (plaque porokeratosis) ● Small asymptomatic keratotic papules enlarging gradually to form plaques with a
raised, wall-like border that resembles a dyke, and an atrophic depressed center (Figures 8.1 and 8.2)
● Solitary or a few lesions ranging in size from millimeters to many centimeters (giant porokeratosis) (Figure 8.3)
● Predilection for face and extremities, including the palms and soles (Figure 8.4)
Linear porokeratosis ● Linear, unilateral or diffuse coalescent keratotic papules, distributed along the
Blaschko’s lines, most commonly on the extremities (Figures 8.5-8.7) ● Loss of heterozygosity is relatively common, revealing exacerbation of the disease and,
rarely, malignant transformation
Punctate palmoplantar porokeratosis (Mantoux) ● Multiple 1-2-mm seed-like keratotic plugs surrounded by a thin raised border (Figures
8.8 and 8.9)
Disseminated superficial porokeratosis ● Widespread, uniform lesions not exceeding 1 cm in diameter occurring in both sun-
exposed and non-sun-exposed areas (Figures 8.10 and 8.11)
Disseminated superficial actinic porokeratosis ● Numerous pruritic papular lesions, enlarging centrifugally, confined to sun-exposed
areas ● Sparing of palms, soles and mucosal surfaces ● Exacerbations during the summer (Figure 8.12)
Onset is usually in childhood; the actinic form appears in the third or fourth decade.