Description

• A multisystem inflammatory disorder most commonly characterized by cutaneous findings of erythematous papules and plaques with silvery scale. A complex genetic and immune-mediated disorder with flares related to systemic, emotional, infectious, and environmental factors. Course may be acute onset/chronic; unpredictable
• Clinical forms:
  • Plaque (vulgaris): Most common variant; symmetrically distributed on scalp, extensor surfaces of extremities, and back
  • Guttate: Usually presents in patients <20 years of age with no history of psoriasis as an acute eruption or as an exacerbation of chronic psoriasis; numerous “droplike” papules and small plaques over trunk; commonly associated with recent streptococcal infection
  • Inverse: Affects intertriginous areas and flexural surfaces; lesions moist ± scales
  • Pustular: Sterile pustules may be acute, generalized, and severe with widespread erythema and scaling in von Zumbusch variant; or less severe and localized to palms and soles; associated with infection and steroid withdrawal
  • Erythrodermic: Generalized erythema and scaling, may require hospital admission for management of dehydration, electrolyte abnormalities, and high risk of infection
  • Nail disease: Pitting, oil spots, and thickening; nails involved in up to 50% of patients with psoriasis
  • Psoriatic arthritis: Seronegative spondyloarthropathy; affects 10–30% of patients with skin involvement; see “Arthritis, Psoriatic” topic

Epidemiology

• Predominant sex: Male = Female
• Seen in all races; greater incidence in whites

• 2–4%
• Predominant age: Bimodal onset between age 20–30 and 50–60; median age of onset 28 years
• ∼80% of patients have mild to moderate disease, with 20% having severe disease (1).

Risk Factors

• Family history
• Local trauma; local irritation
• Infection (streptococcal, viral, HIV)
• Stress (physical and emotional)
• Withdrawal of steroid therapy
• Medications (antimalarials, β-blockers, lithium)
• Smoking
• Diabetes, obesity, metabolic syndrome

• Genetic predisposition (probably polygenic)
• 40% have psoriasis in a 1st-degree relative
• Increased incidence of specific human leukocyte antigens (e.g., HLA-Cw6)
• Multiple susceptibility loci contain genes involved in immune system regulation (e.g., psoriasis-susceptibility (PSORS1) locus on chromosome 6p21

General Prevention

Avoid triggers, including trauma, sunburns, smoking, exposure to certain medications (see above), and stress. Weight loss if obese.

Pathophysiology

Antigenic triggers activate dendritic cells and T cells, promoting a cycle of cytokine production and cell proliferation.

Etiology

Plasmacytoid dendritic cells produce interferon-α, activating myeloid dendritic cells, which in turn produce IL-12 and IL-23, promoting the differentiation of Th1 and Th17. T cells produce cytokines that stimulate keratinocytes to proliferate and produce proinflammatory antimicrobial peptides and cytokines, including TNF-α.

Commonly Associated Conditions

• Psoriatic arthritis
• Obesity, metabolic syndrome, diabetes
• Atherosclerotic disease (2)
• Nonalcoholic fatty liver disease (NAFLD)
• Autoimmune: Alopecia areata, celiac disease, Crohn disease, systemic sclerosis
• Psychiatric/Psychologic: Depression, suicide, emotional burden/anxiety
• Malignancy: Lymphoma, nonmelanoma skin cancer with psoralen-UV-A (PUVA) therapy