• Clinical science



Psoriasis is a common chronic inflammatory skin disorder affecting individuals with an underlying genetic predisposition. The disease manifests following exposure to various triggers (e.g., infection, medication). The typical lesions are sharply demarcated, erythematous, scaly, pruritic plaques, which occur most often on the extensor surfaces of the knees and elbows but may also affect the scalp and back. Other common clinical findings include involvement of the nails (e.g., pitting or discoloration) or joints, which generally manifests with arthritis of the fingers and lower spine. As psoriasis presents with several subtypes, the size, location, and severity of the lesions vary. The diagnosis is based primarily on clinical findings but may also be confirmed with tests (e.g., Auspitz sign) or biopsy. Mild psoriasis is treated with topical agents such as steroids, whereas moderate to severe disease requires systemic therapy (e.g., PUVA, biologics).


  • Prevalence: ∼ 2% of the white population [1][2]
  • Age of onset: 20–40 years [3]

Epidemiological data refers to the US, unless otherwise specified.



Classification of psoriasis [6][7]
Characteristics Psoriasis type I Psoriasis type II
  • Early onset
  • Late onset
  • ∼ 75% of cases
  • ∼ 25% of cases
Genetic predisposition
  • Relatives often affected
  • Relatives rarely affected
Correlation with HLA
  • Strong association with HLA (HLA-Cw6, HLA-B17 and HLA-B57)
  • Rarely correlated with HLA
Clinical presentation
  • Often severe disease
  • Usually mild disease


The mechanism causing the immune response is not yet well understood.


Clinical features

  • Course: relapsing, with symptom-free intervals
  • Lesions: Initially, a few single lesions typically appear, which then often become confluent. [5]
    • Well-demarcated, erythematous lesions, silvery-white scaling plaques, and papules
    • Mainly on scalp, back, elbows, and knees (extensor surfaces) but any other site may be involved [2]
    • Pruritus in ∼ 80% of cases (typically mild, but may also be severe) [9]
    • Lesions characteristically show the Auspitz sign (see “Diagnostics” below for more information).
  • Involvement of nails (in ∼ 50% of cases) [10]

Subtypes and variants

Psoriatic arthritis

If first-degree relatives of patients with psoriasis have joint problems, psoriatic arthritis should be considered.

Cutaneous variants



Differential diagnoses

Differential diagnosis of scaling [5]
Disorder Lesion Distribution
Atopic dermatitis
  • Extensor surfaces of extremities (e.g., shins)
  • Flexural creases (antecubital, popliteal)
Seborrheic dermatitis
  • Clearly demarcated, erythematous plaques, greasy-looking yellow scales
Pityriasis rubra pilaris
  • Typically palms and soles
  • Islands of unaffected skin (sparing)
  • Follicular keratosis
Erythroderma [18]

The differential diagnoses listed here are not exhaustive.


Medical therapy

Mild to moderate psoriasis Moderate to severe psoriasis Severe psoriasis

Systemic treatment is always required for psoriatic arthritis (immunosuppressants and NSAIDs)!


Ultraviolet light is effective in treating dermatological conditions, as it has antiproliferative effects (slowing keratinization) and anti-inflammatory effects (inducing apoptosis of pathogenic T cells) on the skin.



Increased risk of other comorbidities:

We list the most important complications. The selection is not exhaustive.


  • Lifelong disease, usually benign
  • Patients may experience remissions of varying lengths; acute episodes of exacerbation possible.
  • Psoriasis is associated with depression and a decreased quality of life.


  • Avoidance of nicotine and alcohol
  • Regular physical activity
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  • 2. Marks JG Jr, Miller JJ . Lookingbill and Marks' Principles of Dermatology. Saunders Elsevier; 2013.
  • 3. Parisi R, Symmons DP, Griffiths CE, Ashcroft DM. Global epidemiology of psoriasis: a systematic review of incidence and prevalence. J Invest Dermatol. 2013; 133(2): pp. 377–385. doi: 10.1038/jid.2012.339.
  • 4. Hüffmeier U, Lascorz J, Becker T et al. Characterisation of psoriasis susceptibility locus 6 (PSORS6) in patients with early onset psoriasis and evidence for interaction with PSORS1. J Med Genet. 2009; 46(11): pp. 736–744. doi: 10.1136/jmg.2008.065029.
  • 5. Feldman SR. Epidemiology, Clinical Manifestations, and Diagnosis of Psoriasis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/epidemiology-clinical-manifestations-and-diagnosis-of-psoriasis. Last updated December 9, 2015. Accessed May 16, 2017.
  • 6. Hertl M. Autoimmune Diseases of the Skin: Pathogenesis, Diagnosis, Management. Springer Science & Business Media; 2011.
  • 7. Langley RGB. Psoriasis: epidemiology, clinical features, and quality of life. Ann Rheum Dis. 2005; 64(suppl_2): pp. ii18–ii23. doi: 10.1136/ard.2004.033217.
  • 8. Lowes MA, Suárez-Fariñas M, Krueger JG. Immunology of psoriasis. Annu Rev Immunol. 2014; 32: pp. 227–255. doi: 10.1146/annurev-immunol-032713-120225.
  • 9. Roblin D, Wickramasinghe R, Yosipovitch G. Pruritus severity in patients with psoriasis is not correlated with psoriasis disease severity. http://www.jaad.org/article/S0190-9622(13)01012-8/abstract. Updated February 1, 2014. Accessed May 16, 2017.
  • 10. Rosso Schons KR, Faccin Knob C, Murussi N, Costa Beber AA, Neumaier W, Monticielo OA. Nail psoriasis: a review of the literature. An Bras Dermatol. 2014; 89(2): pp. 312–317. doi: 10.1590/abd1806-4841.20142633.
  • 11. Bolognia J, Jorizzo J, Schaffer J. Dermatology: 2-Volume Set. Elsevier; 2012.
  • 12. Gladman DD, Ritchlin C. Clinical manifestations and diagnosis of psoriatic arthritis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-psoriatic-arthritis. Last updated February 12, 2016. Accessed May 16, 2017.
  • 13. Yin Y, Liu S, Xiao H, et al. Opera-Glass Hand in a Patient With Rheumatoid Arthritis. J Clin Rheumatol. 2016; 22(4): p. 215. doi: 10.1097/RHU.0000000000000388.
  • 14. Taylor W, Gladman D, Helliwell P, et al. Classification criteria for psoriatic arthritis: Development of new criteria from a large international study. Arthritis & Rheumatism. 2006; 54(8): pp. 2665–2673. doi: 10.1002/art.21972.
  • 15. Mehlis S. Guttate Psoriasis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/guttate-psoriasis. Last updated November 22, 2016. Accessed September 1, 2017.
  • 16. Hawkes JE, Callis Duffin K. Erythrodermic Psoriasis in Adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/erythrodermic-psoriasis-in-adults. Last updated February 27, 2017. Accessed September 1, 2017.
  • 17. Popescu C, Zofotă S, Bojincă V, Ionescu R. Anti-cyclic citrullinated peptide antibodies in psoriatic arthritis--cross-sectional study and literature review. Journal of medicine and life. 2013; 6(4): pp. 376–82. pmid: 24701255.
  • 18. Davis MDP. Erythroderma in Adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/erythroderma-in-adults. Last updated September 21, 2016. Accessed September 2, 2017.
  • 19. Habashy J. Psoriasis. In: James WD. Psoriasis. New York, NY: WebMD. http://emedicine.medscape.com/article/1943419. Updated April 6, 2017. Accessed May 16, 2017.
  • 20. Feldman SR. Treatment of Psoriasis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. http://www.uptodate.com/contents/treatment-of-psoriasis. Last updated March 11, 2017. Accessed May 16, 2017.
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last updated 11/18/2020
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