• A chronic, inflammatory disorder commonly characterized by cutaneous erythematous plaques with silvery scale with varying phenotypes and severity
  • Clinical phenotypes
    • Plaque (vulgaris): most common variant (~80% of cases); well-demarcated, red plaques with silvery scale; symmetrically distributed commonly on the scalp, extensor surfaces, and trunk
    • Guttate: <2% of psoriasis patients, usually in patients <30 years of age; presents abruptly with 1- to 10-mm droplet-shaped erythematous papules with fine scale over trunk and extremities; often preceded by group A β-hemolytic streptococcal infection 2 to 3 weeks prior. Most cases resolve spontaneously.
    • Inverse: affects intertriginous areas and flexural surfaces; pink-to-red plaques with minimal scale; absence of satellite pustules distinguishes it from candidiasis.
    • Erythrodermic: generalized erythema and scaling, affecting 90% of body surface area (BSA) or more; associated with desquamation; hair loss; nail dystrophy; and systemic symptoms such as fever, chills, malaise, lymphadenopathy, and/or high-output cardiac failure
    • Pustular: sterile pustules; several forms including generalized pustular psoriasis, localized pustular psoriasis, and impetigo herpetiformis (in pregnancy); generalized type can result in life-threatening bacterial superinfections.
    • Nail disease: pitting, oil spots, and onycholysis; nails involved in up to 50% of patients with psoriasis with lifetime incidence of 80–90%; increased association with psoriatic arthritis


Predominant sex: female > male; predominant age: two peaks of incidence between the ages of 20 to 30 years and 50 to 60 years


  • 2–4% prevalence in the United States
  • In the United States, the most commonly affected demographic group is non-Hispanic Caucasian.

Etiology and Pathophysiology

Psoriasis is a complex immune-mediated disorder with interactions between dendritic cells, T lymphocytes, neutrophils, and keratinocytes that results from a polygenic predisposition in the setting of environmental triggers; associated with relapsing flares related to systemic, psychological, infectious, and environmental factors


  • Genetic predisposition (polygenic)
  • 40% have psoriasis in a first-degree relative.
  • Multiple susceptibility loci contain genes involved in immune system regulation.
  • HLA-C*06 is most strongly correlated with early onset psoriasis.

Risk Factors

  • Family history
  • Obesity
  • Local trauma; local irritation (Koebner phenomenon)
  • HIV
  • Streptococcal infection
  • Stress (may contribute to exacerbation)
  • Medications (lithium, antimalarials, β-blockers, interferon, TNF-α inhibitors, withdrawal of steroids)
  • Smoking
  • Alcohol abuse

General Prevention

Control cardiovascular risk factors. Avoidance of triggers including trauma, sunburns, smoking, and exposure to certain medications, alcohol, and stress.

Commonly Associated Conditions

  • Psoriatic arthritis
  • Seborrheic dermatitis
  • Obesity, metabolic syndrome, diabetes, chronic kidney disease
  • Cardiovascular disease, atherosclerotic disease
  • Nonalcoholic fatty liver disease (NAFLD)
  • Other autoimmune conditions: Crohn disease, ulcerative colitis, ankylosing spondylitis
  • Psychiatric/psychological conditions: depression, anxiety, suicidal ideation, poor self-esteem, emotional burden/anxiety, alcohol abuse, sexual dysfunction
  • Myopathy

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