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Other dermatoses


Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC, Eastern Health, St. Johns (Canada) (see Reviewers page)
Revised: 2 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Clinical features

● 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


● Photochemotherapy (psoralen) and ultraviolet A light (PUVA) - associated with increased risk of melanoma and squamous cell carcinoma

Clinical description

● Well demarcated erythematous plaques covered by fine, loosely adherent, silvery-white scales

Clinical images

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

Contributed by Angel Fernandez-Flores, MD, PhD, Hospital El Bierzo and Clinica Ponferrada, Spain

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

eMedicine-pustular psoriasis

End of Skin-nontumor > Other dermatoses > Psoriasis

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