Last updated: September 30, 2021

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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.


  • Course: relapsing, with symptom-free intervals
  • Lesions: Initially, a few single lesions typically appear, which then often become confluent.
    • 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]

Psoriatic arthritis

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

Cutaneous variants

  • Plaque psoriasis: most common variant characterized by symmetrically distributed, thick, scaly, erythematous lesions [11]
  • Guttate psoriasis
    • Lesions the size of drops of water
    • May develop into psoriasis
    • Occurs mainly in children and adolescents after streptococcal infection
  • Erythrodermic psoriasis
  • Inverse psoriasis: : mainly affects skin folds and flexural creases of large joints (flexural psoriasis)
  • Pustular psoriasis

Differential diagnosis of scaling
Disorder Lesion Distribution
Atopic dermatitis
  • Extensor surfaces of extremities (e.g., shins)
  • Flexural creases (antecubital, popliteal)
Seborrheic dermatitis
Pityriasis rubra pilaris
  • Typically palms and soles
  • Islands of unaffected skin (sparing)
  • Follicular keratosis
Erythroderma [16]

The differential diagnoses listed here are not exhaustive.


Treatment choice depends on disease severity, with consideration for patient preference and response to treatment.

Overview of psoriasis treatment
Treatment approach Agents
Mild psoriasis (< 3% body surface area involvement)
  • Topical treatment with ointments (e.g., petroleum jelly) and moisturizers to prevent moisture loss
  • Topical application of medications
Moderate psoriasis (3–10% body surface area involvement)
  • Topical application of more than one medication (combination therapy)
  • See above for topical agents.
  • Addition of systemic agents as needed
Severe psoriasis (> 10% body surface area involvement)
  • Topical PLUS systemic treatment
  • See "Moderate psoriasis” above for topical and systemic agents.

Psoriatic arthritis always requires systemic treatment.


Ultraviolet light is effective in treating dermatological conditions due to its antiproliferative (e.g., slowing of keratinization) and antiinflammatory effects (e.g., inducing apoptosis of pathogenic T cells).


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.
  1. James WD, Berger T, Elston D. Andrews' Diseases of the Skin: Clinical Dermatology. Elsevier Health Sciences ; 2015
  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): p.377-385. doi: 10.1038/jid.2012.339 . | Open in Read by QxMD
  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): p.736–744. doi: 10.1136/jmg.2008.065029 . | Open in Read by QxMD
  5. Feldman SR. Epidemiology, Clinical Manifestations, and Diagnosis of Psoriasis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. 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): p.ii18-ii23. doi: 10.1136/ard.2004.033217 . | Open in Read by QxMD
  8. Lowes MA, Suárez-Fariñas M, Krueger JG. Immunology of psoriasis. Annu Rev Immunol. 2014; 32 : p.227-255. doi: 10.1146/annurev-immunol-032713-120225 . | Open in Read by QxMD
  9. Pruritus severity in patients with psoriasis is not correlated with psoriasis disease severity. 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): p.312-317. doi: 10.1590/abd1806-4841.20142633 . | Open in Read by QxMD
  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. 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 . | Open in Read by QxMD
  14. Taylor W, Gladman D, Helliwell P, et al. Classification criteria for psoriatic arthritis: Development of new criteria from a large international study. Arthritis Rheum. 2006; 54 (8): p.2665-2673. doi: 10.1002/art.21972 . | Open in Read by QxMD
  15. 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): p.376-82.
  16. Davis MDP. Erythroderma in Adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: September 21, 2016. Accessed: September 2, 2017.
  17. Inamadar AC, Palit A, Ragunatha S. Textbook of Pediatric Dermatology. JP Medical Ltd ; 2014

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