Psoriasis



Psoriasis


Cary Chisholm, MD





Key Facts


Terminology



  • Synonym: Psoriasis vulgaris


Clinical Issues



  • Incidence



    • 1-3% of the population is affected


  • Age



    • Mean age of presentation: 25-35 years


  • Presentation



    • Sharply demarcated erythematous plaques and patches


    • Overlying silvery white scale


    • Auspitz sign: Pinpoint bleeding occurs when scale is removed


  • Site



    • Extensor surfaces of the extremities, scalp, trunk, nails, and buttocks


Microscopic Pathology



  • Epidermis



    • Confluent parakeratosis


    • Regular psoriasiform hyperplasia with thinning over dermal papillae


    • Neutrophils migrating through epidermis over dermal papillae


    • Neutrophil collections in the corneal (Munro microabscesses) and spinous (spongiform pustules of Kogoj) layers


  • Dermis



    • Dilated vessels in papillary dermis


    • ± RBC extravasation


    • Denser perivascular activated lymphocytes, Langerhans cells, and neutrophils







Psoriasis presents here as an ostraceous, silvery-white, adherent, thick scale image over the knuckles on erythematous plaques image in the usual extensor location.






In this psoriasis vulgaris plaque, psoriasiform hyperplasia is evident with thinning of the suprapapillary plates image, confluent parakeratosis image, and superficial perivascular lymphocytes and neutrophils.


TERMINOLOGY


Synonyms



  • Psoriasis vulgaris


Definitions



  • Prototype of psoriasiform dermatoses


ETIOLOGY/PATHOGENESIS


Environmental/Lifestyle Associations



  • Stress


  • Comorbidities of metabolic syndrome



    • Obesity, hypertension, diabetes mellitus, dyslipidemia, cardiovascular disease


  • Some organisms



    • Viruses: HPV5, HPV36, and HIV


    • Bacteria: Streptococcus pyogenes, Staphylococcus aureus


    • Fungi: Malassezia spp., Candida albicans


  • Trauma



    • Koebner reaction: Present in 1/3 of cases


  • Medications



    • Particularly β-blockers, ACE-inhibitors, clonidine, nonsteroidal anti-inflammatory drugs, anti-malarials, and some β-lactam antibiotics


Genetic



  • Extremely complicated and ever evolving


  • Polygenic, but more common in monozygotic than dizygotic twins


  • HLA-Cw6



    • Psoriasis vulgaris, guttate psoriasis


    • Earlier disease onset


    • Penetrance only 10-15%


  • Interleukin (IL)-23α subunit, IL-12/23 shared β subunit, IL-23 receptor subunit



    • Critical role in mounting a T-cell response


    • Other gene products that interact with these subunits are also implicated


  • IL-4 and IL-13 polymorphisms



    • Important role in forming and mediating effects of the Th2 T-cell subset


    • Also leads to downregulation of Th1 T cells


  • Downstream signaling mediators of tumor necrosis factors (TNF)



    • TNIP1 and TRAF3IP2


Immunological



  • Very complex; a detailed explanation is beyond the scope of this chapter


  • T cells are recruited to the superficial dermal vessels



    • CD4(+) T cells mostly remain in the dermis


    • CD8(+) T cells infiltrate the epidermis


  • Dermal dendritic cells exacerbate CD4 T-cell recruitment and cytokine cascade



    • Plasmacytoid dendritic cells produce interferon (IFN)-α


    • Langerhans cells stimulate IL-22 producing T cells


    • Myeloid dendritic cells produce TNF-α, produce and stimulate multiple cytokines, stimulate T cells, and increase IFN-γ


  • Increase in cytokines causes keratinocyte proliferation and epidermal hyperplasia


CLINICAL ISSUES

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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Psoriasis

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