Skin nontumor
Spongiotic, psoriasiform and pustular reaction patterns

Topic Completed: 1 August 2011

Minor changes: 9 November 2020

Copyright: 2002-2020,, Inc.

PubMed Search: Psoriasis skin [title]

Mowafak Hamodat, M.B.Ch.B., M.Sc.
Page views in 2019: 33,781
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Cite this page: Hamodat M. Psoriasis. website. Accessed December 5th, 2020.
Definition / general
  • Common; affects 1% of population, all ages
  • Also called psoriasis vulgaris
  • Chronic, bilaterally symmetric, nonpruritic 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

Contributed by Mark R. Wick, M.D.

Breast skin

Images hosted on other servers:

Guttate psoriasis

Microscopic (histologic) 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
Microscopic (histologic) images

Contributed by Hillary Rose Elwood, M.D.

Classic features of psoriasiform hyperplasia, confluent parakeratosis, loss of granular layer and dilated capillaries with thinned suprapapillary plate

Contributed by Angel Fernandez-Flores, M.D., Ph.D.

Various Images

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
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