DESCRIPTION

• A chronic relapsing skin disease most often characterized by thick white scales over erythematous plaques often involving elbows, knees, and scalp (i.e., psoriasis vulgaris); in children, psoriasis may present with less scaling and more erythema than in adults; may also present as diaper rash
• Other variants include the following:
  • Guttate psoriasis—drop-like plaques on the chest, back, and limbs; often follows group A streptococcal infections in children (i.e., strep throat)
  • Inverse psoriasis—lesions in flexures, also called intertriginous
  • Erythrodermic psoriasis—a severe variant with widespread erythematous skin involvement often accompanied by fever; can be life-threatening
  • Pustular psoriasis—generalized or localized, often affecting palms and soles; potentially lethal
  • Psoriatic arthritis—joint pain can precede skin involvement.

EPIDEMIOLOGY

• Involves both genders equally
• Onset of psoriasis is bimodal, commonly presenting in the 3rd decade with a smaller second peak of onset in the 6th decade; however, it can present at any age. Mean age of onset in children is 8.1 years.
• Earlier onset is associated with more severe disease.
• Psoriasis is universal in occurrence, but prevalence varies in different populations. The average prevalence in the United States is ~1–3%.

ETIOLOGY

The pathogenesis is unknown, possibly an immune-mediated inflammatory disease. Genetic factors are important. Well-defined trigger factors include the following:

• Trauma—psoriasis can develop in areas of trauma (i.e., isomorphic response, sometimes called the Koebner phenomenon).
• Infections (e.g., upper respiratory infections, Streptococcus pyogenes, HIV)
• Stress
• Winter in colder climates in Northern Hemisphere
• Some drugs (i.e., systemic corticosteroids, lithium, nonsteroidal anti-inflammatory drugs (NSAIDs), and antimalarials)

RISK FACTORS

PATHOPHYSIOLOGY

• Plaque-type psoriasis is characterized by a thickened parakeratotic epidermis with an absent granular layer above dermal papillae containing dilated tortuous capillaries.
• Collections of polymorphonuclear leukocytes extend from the dermal papillae into the epidermidis stratum corneum (i.e., Munro microabscesses).
• A mixed perivascular infiltrate is confined to the papillary dermis.

COMMONLY ASSOCIATED CONDITIONS

• Obesity
• Metabolic syndrome
• Hypertension
• Depression
• Anxiety
• Uveitis
• Arthritis
• Rheumatoid arthritis
• Crohn disease
• Diabetes mellitus
• Lymphoma (rare)