Psoriasis
Epidemiology:
- 1-2% of US population
- all ages
Common sites:
- elbows
- knees
- scalp
- lumbosacral areas
- intergluteal cleft
- glans penis
Gross features:
- well-demarcated
- pink to salmon-coloured plaque
- loosely adherent
silver-white scales
- multiple punctate bleeding sites when scale peeled off (Auspitz sign)
- variations:
- annular
- linear
- gyrate
- serpiginous
- erythroderma sometimes
- nail changes (30%):
- yellow-brown discolouration (oil slick)
- pitting, dimling
- thickening
- crumbling
- onycholysis (separation of the nail plate from
underlying bed)
- pustular psoriasis:
- multiple small
pustules on erythematous plaques
- hands and feet
or generalized (life-threatening)
Histologic features:
- acanthosis
- regular downward
elongation of the rete ridges
- thinning of
epidermis overlying tips of dermal papillae with dilated, tortuous blood
vessels within these papillae
- mitotic figures well above the basal
layer
- stratum granulosum is thinned or absent
- extensive overlying
parakeratotic scale
- small aggregates
of neutrophils in superficial epidermis and
within parakeratotic stratum corneum
- associated spongiotic foci (spongiform pustules)
- (Munro microabscesses within parakeratotic
stratum corneum)
- pustular psoriasis:
- large
abscess-like collections of neutrophils
directly beneath the stratum corneum
Immunophenotype:
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Marker:
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Sensitivity:
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Specificity:
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Molecular features:
- Strong association
with HLA-Cw*0602 allele (66% of psoriasis
patients) (10% of carriers develop psoriasis)
Other features:
- Extracutaneous associations:
- Arthritis
- Myopathy
- Enteropathy
- Spondylitic joint disease
- Acquired immunodeficiency
syndrome
- T cell mediated
- TH1-dominated
cytokine “soup”
- High levels of
TNF
References: