Porokeratosis

Porokeratosis
George R. Collins, DO
Joseph Susa, DO
Clay J. Cockerell, MD
Key Facts
Terminology
  • Porokeratosis: Genodermatosis with clonal keratinocytes resulting in clinically and morphologically distinct keratinization disorder
  • Several clinical variants of porokeratosis with overlapping features exist among described varieties
Clinical Issues
  • Porokeratosis of Mibelli manifests as 1 or more asymptomatic large, round to oval, skin-colored to red to brown, annular plaques often occurring unilaterally on extremities
  • DSAP has many superficial, coalescent, small, thin, keratotic, skin-colored to red to brown annular plaques or papules with peripheral cornoid lamella occurring bilaterally on sun-exposed extremities
  • Porokeratosis has prolonged course, is hard to treat
Microscopic Pathology
  • Cornoid lamella is the hallmark feature of all variants and corresponds to clinically evident raised hyperkeratotic peripheral ridge of lesion
  • Cornoid lamella is a thin, compact column of parakeratosis; granular layer is absent to decreased, and dyskeratotic keratinocytes are present at the base
Top Differential Diagnoses
  • Cornoid lamella are not specific for porokeratosis and can be seen in neoplastic (actinic keratosis, carcinomas) or reactive (viral warts) squamous proliferations as well as in normal skin
  • Benign lichenoid keratosis and clinically linear lesions are also in differential diagnosis
Disseminated superficial actinic porokeratosis presents here as multiple, small, well-demarcated, erythematous, annular plaques image with raised hyperkeratotic peripheral ridges (cornoid lamellae).
Porokeratosis of Mibelli demonstrates a sharply demarcated oval plaque with an erythematous center surrounded by a raised, hyperkeratotic, peripheral ridge that represents the cornoid lamella image.
TERMINOLOGY
Abbreviations
  • Disseminated superficial actinic porokeratosis (DSAP), disseminated superficial porokeratosis (DSP), porokeratosis palmaris et plantaris disseminata (PPPD), punctate porokeratosis (PP), linear porokeratosis (LP)
Synonyms
  • Inclusive term “porokeratosis” may be used to refer to any or all of the various distinct clinical variants of porokeratosis
Definitions
  • Genodermatosis with clonal keratinocytic proliferation resulting in a clinically and morphologically distinct keratinization disorder
    • Hyperkeratotic plaques or papules surrounded by centrifugally expansile, thread-like, raised border that results in characteristic cornoid lamella
  • Several clinical variants of porokeratosis with overlapping features exist among described varieties
    • Classic variant: Porokeratosis of Mibelli
    • Common disseminated variants: Disseminated superficial actinic porokeratosis and disseminated superficial porokeratosis
    • Rare variants: Porokeratosis palmaris et plantaris disseminata, linear porokeratosis, localized porokeratosis, punctate porokeratosis, CAP syndrome, reticulate form, and many others
ETIOLOGY/PATHOGENESIS
Developmental Anomaly
  • Genetically heterogeneous condition that may be familial and tends to be inherited in autosomal dominant manner
  • Fully penetrant by 4th decade of life
  • Pathogenetic mechanisms are still somewhat unclear
  • Multiple current proposed concepts of pathogenetic mechanisms
    • Loci at chromosome bands 12q23.2-24.1 and 15q25.1-26 (DSAP1 and DSAP2) described in familial disseminated superficial actinic porokeratoses
      • Locus at DSAP1 corresponds to SART3, a candidate gene encoding a tumor rejection antigen and felt to be involved in regulation of mRNA splicing
      • SART3 mutations may thus result in altered proliferation and transformation of epithelial cells
    • Locus identified for disseminated superficial porokeratosis (DSP) at 18p11.3
    • Centrifugal expansion of cornoid lamellae in lesions may reflect migration of mutant clone of keratinocytes based on DNA ploidy and chromosome abnormalities
    • Higher prevalence of porokeratosis in immunosuppressed patients suggests impaired immunity, which permits disease in genetically predisposed
  • CAP syndrome (craniosynostosis, anal anomalies, and porokeratosis) is a rare genodermatosis found in only a few ethnically diverse families so far
    • Main phenotypic features are craniosynostosis and clavicular hypoplasia, anal anomalies, and widespread, small porokeratotic papules affecting face and extremities starting at 1 month of age
CLINICAL ISSUES
Epidemiology
  • Incidence
    • Relatively common pathological process
      • Disseminated superficial actinic porokeratosis is most common clinical variant
  • Age
    • Classic porokeratosis of Mibelli and rare linear porokeratosis variant begin during infancy or childhood with expansion of lesions in adulthood
    • DSAP and DSP variants often develop during 3rd or 4th decade of life
    • Porokeratosis palmaris et plantaris disseminata and punctate porokeratosis variants appear during adolescence and early adulthood
  • Gender
    • Porokeratosis of Mibelli and porokeratosis palmaris et plantaris disseminata show male predilection
    • DSAP and DSP both show female predilection: F:M = 3:1
Site
  • Distribution and site of lesions varies depending on clinical variant of porokeratosis
    • Porokeratosis of Mibelli develops as one or more round to oval plaques unilaterally on extremities
    • DSAP is typically widely distributed symmetrically over sun-exposed areas of extremities, with rare facial involvement and usual sparing of palms, soles, and mucous membranes
    • DSP occurs symmetrically on extremities similar to DSAP, but sun-protected areas are not spared
Presentation
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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Porokeratosis

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