Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth ... Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth et al., 1997). However, as noted by Sybert (2010), the existence of several families with expression of more than one variant of porokeratosis among members, and individuals expressing more than one variant, suggest that the distinctions among these variants may be artificial. Disseminated superficial actinic porokeratosis (DSAP) is the most common subtype of porokeratosis. It is characterized by multiple small, annular, anhidrotic, keratotic lesions that are located predominantly on sun-exposed areas of the skin, such as the face, neck, and distal limbs. The lesions typically begin to develop in adolescence and reach near-complete penetrance by the third or fourth decade of life (summary by Wu et al., 2004 and Zhang et al., 2012). For a discussion of genetic heterogeneity of porokeratosis, see 175800.
Luan et al. (2011) reported a 4-generation Chinese family from the Anhui province with disseminated superficial actinic porokeratosis. The average age at onset was 28 years, but the earliest onset was at age 16. The skin lesions were ... Luan et al. (2011) reported a 4-generation Chinese family from the Anhui province with disseminated superficial actinic porokeratosis. The average age at onset was 28 years, but the earliest onset was at age 16. The skin lesions were small, conically shaped papules, 1 to 3 mm in diameter, that enlarged centrifugally over months or years, leaving a central atrophic area and a well-defined irregular keratotic rim. Most lesions were on the extremities, especially distally on the extensor and lateral surfaces. The face, neck, and trunk were also affected, but the palms, soles, and oral mucosal surfaces were spared. The lesions become more prominent with sunlight exposure. There was intrafamilial variation in the number of lesions and severity of disease. The proband, who had DSAP, also developed linear atrophic plaques along the left side of her leg after left foot trauma as a teen. Histologic specimens of both DSAP and the linear lesions from the proband showed an invagination of the epidermis containing a column of parakeratotic cells overlying an absent granular layer. There was no malignant transformation in the linear lesion. None of the other affected family members had linear lesions.