Description

• A chronic, inflammatory disorder most commonly characterized by cutaneous erythematous plaques with silvery scale. It is a complex immune-mediated disorder that results from a polygenic predisposition in the setting of environmental triggers. It is associated with relapsing flares related to systemic, psychological, infectious, and environmental factors; a skin disease with multiple phenotypic variations and degrees of severity
• Clinical phenotypes
  • Plaque (vulgaris): most common variant (~80% of cases); well-demarcated, red plaques with thick, silvery scale; symmetrically distributed most commonly on the scalp, extensor surfaces of extremities, and trunk
  • Guttate: <2% of psoriasis patients, usually in patients <30 years of age; presents abruptly with 1- to 10-mm droplet-shaped pink 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 although may coexist.
  • 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; usually requires hospital admission for management of dehydration, electrolyte abnormalities, and risk of infection
  • 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, sepsis, and dehydration if left untreated.
  • 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
  • Psoriatic arthritis: 5–30% of patients; most commonly asymmetrical oligoarthritis involving the hands and feet

Epidemiology

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

• 2–4%—similar prevalence in all races in the United States
• Estimated 125 million affected worldwide

Etiology and Pathophysiology

Psoriasis is a complex immune-mediated disorder with interactions between dendritic cells, T lymphocytes, neutrophils, and keratinocytes. It is considered a TH1- and TH17-driven disease with numerous cytokines including TNF-α, interferon-γ, IL-12, IL-17, and IL-23 playing pathogenic roles resulting in an inflammatory, hyperproliferative state.

• Genetic predisposition (polygenic)
• 40% have psoriasis in a first-degree relative.
• Multiple susceptibility loci contain genes involved in immune system regulation (e.g., psoriasis susceptibility [PSORS1 locus on chromosome 6p21; polymorphisms in the IL-12/IL-13 receptor, the p40 subunit of IL-12 and IL-23, and the p19 subunit of IL-12) (1).
• HLA-C*06 is most strongly correlated with early-onset psoriasis.

Risk Factors

Family history, obesity (may contribute to more severe disease), local trauma; local irritation (Koebner phenomenon), HIV, streptococcal infection, mental stress (may contribute to exacerbation), medications (lithium, antimalarials, β-blockers, interferon, TNF-α inhibitors, withdrawal of steroids), smoking, alcohol abuse

General Prevention

Avoid triggers, including trauma, sunburns, smoking, and exposure to certain medications, alcohol, and stress; weight loss if obese

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