Skin tumor Nonmelanocytic
Benign (nonmelanotic) epidermal tumors or tumor-like lesion

Author: Mowafak Hamodat, M.D., MB.CH.B, MSc., FRCPC (see Authors page)

Revised: 22 May 2017, last major update August 2011

Copyright: (c) 2002-2017,, Inc.

PubMed Search: Porokeratosis

Cite this page: Porokeratosis. website. Accessed October 20th, 2018.
Definition / general
  • Rare disease, consists of an atrophic center bordered by a peripheral grooved keratotic ridge
  • Six major categories: classic, localized, linear, punctuate, disseminated superficial porokeratosis and disseminated superficial actinic porokeratosis
  • May be associated with a slight increase in neoplasia (basal cell and squamous cell carcinoma, Bowen's disease)
  • May develop against a background of solid organ transplantation or blood transfusion, possibly related to hepatitis C infection
Microscopic (histologic) description
  • Recommended to biopsy peripheral grooved ridge to see classic features
  • Keratin-filled epidermal invagination with an angulated, parakeratotic tier (cornoid lamella)
  • Epithelium deep to the tier is vacuolated and devoid of a granular cell layer
  • Adjacent epithelium towards the center is either atrophic, normal thickness or acanthotic
  • Dyskeratotic cells may be seen
  • Liquefactive degeneration of the basal cell layer is present; may be conspicuous cytoid bodies
  • Dermis shows a non-specific inflammatory cell infiltrate with telangiectatic vessels
  • In actinic variant, is often solar elastosis and atrophy of adjacent epidermis
Microscopic (histologic) images

Images hosted on PathOut servers:

Courtesy of Angel Fernandez-Flores, M.D.

Differential diagnosis
  • Cornoid lamella formation: also seen in seborrheic warts, solar keratosis, veruca vulgaris, squamous cell carcinoma and basal cell carcinoma, porokeratotic eccrine nevi