• 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
  • Age of onset: 20–40 years


Epidemiological data refers to the US, unless otherwise specified.





Clinical features

  • Course: relapsing, with symptom-free intervals
  • Well-demarcated, erythematous lesions, and silvery-white scaling plaques
    • Initially, a few single lesions typically appear, which then often become confluent.
    • Mainly on scalp, back, elbows, and knees (extensor surfaces), but any other site may be involved
    • Pruritus in ∼ 80% of cases (typically mild, but may also be severe)
  • Involvement of nails (in ∼ 50% of cases)


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
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


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.




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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last updated 09/17/2020
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