Skin-nontumor / Clinical dermatology
Other dermatoses

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

Revised: 20 July 2016, last major update August 2011

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Psoriasis [title] skin

Cite this page: Psoriasis. website. Accessed October 26th, 2016.
Definition / General
  • Common; affects 1% of population, all ages
  • Also called psoriasis vulgaris
  • Chronic, bilaterally symmetric, non-pruritic lesion of unknown etiology of elbows, knees, umbilicus, lower back, scalp and glans penis
  • Associated with arthritis, myopathy, enteropathy, spondylitic heart disease and AIDS
  • 30% have nail discoloration and onycholysis
  • Usually not biopsied unless atypical
  • Either localized (hands / feet) or generalized and possibly life threatening with fever, leukocytosis, diffuse infections, secondary infections and electrolyte disturbances
  • Auspitz sign: bleeding when scale is lifted from plaque
  • Koebner phenomenon: new lesions at site of trauma
  • Parapsoriasis: similar morphologically, but no pain or itching; small plaque variants are considered benign
  • Pustular psoriasis: rare; prominent small pustules in plaque
  • Note: large plaque variants and parapsoriasis variegata are considered early stages of cutaneous T-cell lymphoma
Clinical Features
  • Well demarcated erythematous plaques covered by fine, loosely adherent, silvery-white scales
  • Photochemotherapy (psoralen) and ultraviolet A light (PUVA) - associated with increased risk of melanoma and squamous cell carcinoma
Clinical Images

Images hosted on PathOut servers:

Breast skin, courtesy of Mark R. Wick, M.D.

Images hosted on other servers:

Guttate psoriasis

Micro Description
  • Parakeratosis without hyperkeratosis, acanthosis with downward elongation of rete ridges (resembles a comb), thin/no granular cell layer, suprapapillary thinning (attenuated layer of epidermal cells above tips of dermal papillae), Munro microabscesses (neutrophils in parakeratotic scale)
  • Increased mitotic figures above basal layer
  • Prominent dermal capillaries, mixed dermal infiltrate of lymphocytes, macrophages and neutrophils
Micro Images

Images hosted on PathOut servers:

Breast skin, courtesy of Mark R. Wick, M.D.

Courtesy of Angel Fernandez-Flores, M.D., Ph.D.

Differential Diagnosis
  • Psoriasiform lesions:
    • Pityriasis rubra pilaris: has parakeratosis and hyperkeratosis in both vertical and horizontal directions; no neutrophils in stratum corneum unless secondary infection
    • Lichen simplex chronicus: scarring of dermal papillae due to persistent rubbing; no thinning of suprapapillary plate; hyperkeratosis and hypergranulosis are often marked, minimal parakeratosis unless background of spongiosis
    • Papulosquamous drug eruption: due to lithium or propranolol, may resemble psoriasis but has moderate/high number of eosinophils; may have seborreic dermatitis, psoriasiform hyperplasia or corneal neutrophils; has conspicuous spongiotic component (psoriasis has only mild component in early lesions); if distinction not impossible, call sebo-psoriasis
    • Pustular psoriasis: resembles pustular dermatophytosis, bacterial impetigo and pustular drug eruption; use gram stain, PAS, culture, clinical history to differentiate
    • Subcorneal pustular dermatosis: has spongiform change or degeneration, but pustular psoriasis does not
Additional References