Porokeratosis is a chronic progressive disorders of keratinization characterized clinically by hyperkeratotic papules or plaques surrounded by a threadlike, elevated border that expands centrifugally.
Porokeratosis is genetically heterogeneous; the majority are inherited as autosomal dominant traits.
At least six clinical variants of porokeratosis have been described.
The classic form, porokeratosis of Mibelli, presents in infancy or childhood as asymptomatic, small, brown to skin-colored, annular papules with a characteristic raised border.
The most common type, disseminated superficial actinic porokeratosis, presents with multiple papules distributed symmetrically on sun-exposed areas.
Linear porokeratosis presents at birth or in childhood with lesions distributed along Blaschko lines.
Punctate porokeratosis appears during or after adolescence as 1- to 2-mm papules on the palms or soles.
In all variants, a thin column of parakeratotic cells (cornoid lamella) corresponds to the hyperkeratotic border and extends throughout the stratum corneum in histologic sections.
Malignant epithelial neoplasms are reported in all subtypes except the punctate variety.
Porokeratosis is a morphologically distinct disorder of keratinization characterized clinically by hyperkeratotic papules or plaques surrounded by a threadlike elevated border that expands centrifugally. Histologically, a thin column of parakeratotic cells extends throughout the stratum corneum and is seen in all variants. This distinctive histopathologic feature, known as the cornoid lamella, corresponds to the raised hyperkeratotic border evident clinically.
At least six clinical variants of porokeratosis are recognized, and recent genetic progress has additionally allowed classification according to the underlying mutation (Table 51-1). Reports of one type of porokeratosis coexisting with other forms and different types developing in multiple members of an affected family suggest more similarities than disparities, particularly in the disseminated forms. Thus, it is important to allow for some flexibility around clinical subcategorization.1-3
Table 51-1Clinical Variants of Porokeratosis and Genes and Genetic Loci Identified to Date ||Download (.pdf) Table 51-1 Clinical Variants of Porokeratosis and Genes and Genetic Loci Identified to Date
|CONDITION ||GENE ||LOCUS ||OMIM ||INHERITANCE |
|Porokeratosis 1 (porokeratosis of Mibelli) ||PMVK ||1q21.3 ||175800 ||AD |
|Porokeratosis 2 (porokeratosis palmaris et plantaris disseminata) ||Not yet identified ||12q24.1–q24.2 ||175850 ||AD |
|Porokeratosis 3 (disseminated superficial actinic porokeratosis 1) ||MVK ||12q24.11 ||175900 ||AD |
|Porokeratosis 4 (disseminated superficial actinic porokeratosis 2) ||Not yet identified ||15q25.1–15q26.1 ||607728 ||AD |
|Porokeratosis 5 (disseminated superficial actinic porokeratosis 3) ||Not yet identified ||1p31.3–1p31.1 ||612293 ||AD |
|Porokeratosis 6 (disseminated superficial porokeratosis) ||Not yet identified ||18p11.3 ||612353 ||AD |
|Porokeratosis 7 (multiple types) ||MVD ||16q24.2 ||614714 ||AD |
|Porokeratosis 8 (disseminated superficial actinic porokeratosis 4) ||SLC17A9 ||20q13.33 ||616063 ||AD |
|Porokeratosis 9 (multiple types) ||FDPS ||1q22 ||616631 || |
|CDAGS syndrome ||?RUNX2 ||22q12–22q13 ||603116 ||AR |