Psoriasis

Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by patches of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small localized patches to complete body coverage. Injury to the skin can trigger psoriatic skin changes at that spot, which is known as the Koebner phenomenon.

Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by patches of abnormal skin.[4][5] These areas are red, pink, or purple, dry, itchy, and scaly.[3][8] Psoriasis varies in severity from small localized patches to complete body coverage.[3] Injury to the skin can trigger psoriatic skin changes at that spot, which is known as the Koebner phenomenon.[9]

The five main types of psoriasis are plaque, guttate, inverse, pustular, and erythrodermic.[5] Plaque psoriasis, also known as psoriasis vulgaris, makes up about 90% of cases.[4] It typically presents as red patches with white scales on top.[4] Areas of the body most commonly affected are the back of the forearms, shins, navel area and scalp.[4] Guttate psoriasis has drop-shaped lesions.[5] Pustular psoriasis presents as small, noninfectious, pus-filled blisters.[10] Inverse psoriasis forms red patches in skin folds.[5] Erythrodermic psoriasis occurs when the rash becomes very widespread and can develop from any of the other types.[4] Fingernails and toenails are affected in most people with psoriasis at some point in time.[4] This may include pits in the nails or changes in nail color.[4]

Psoriasis is generally thought to be a genetic disease that is triggered by environmental factors.[3] If one twin has psoriasis, the other twin is three times more likely to be affected if the twins are identical than if they are nonidentical.[4] This suggests that genetic factors predispose to psoriasis.[4] Symptoms often worsen during winter and with certain medications, such as beta blockers or NSAIDs.[4] Infections and psychological stress can also play a role.[3][5] The underlying mechanism involves the immune system reacting to skin cells.[4] Diagnosis is typically based on the signs and symptoms.[4]

There is no known cure for psoriasis, but various treatments can help control the symptoms.[4] These treatments include steroid creams, vitamin D3 cream, ultraviolet light, immunosuppressive drugs, such as methotrexate, and biologic therapies targeting specific immunologic pathways.[5] About 75% of skin involvement improves with creams alone.[4] The disease affects 2–4% of the population.[7] Men and women are affected with equal frequency.[5] The disease may begin at any age, but typically starts in adulthood.[5] Psoriasis is associated with an increased risk of psoriatic arthritis, lymphomas, cardiovascular disease, Crohn's disease, and depression.[4] Psoriatic arthritis affects up to 30% of individuals with psoriasis.[10]

The word "psoriasis" is from Greek ψωρίασις meaning 'itching condition' or 'being itchy',[11] from psora 'itch', and -iasis 'action, condition'.

Signs and symptoms

Plaque psoriasis

Psoriasis vulgaris (also known as chronic stationary psoriasis or plaque-like psoriasis) is the most common form and affects 85–90% of people with psoriasis.[12] Plaque psoriasis typically appears as raised areas of inflamed skin covered with silvery-white, scaly skin. These areas are called plaques and are most commonly found on the elbows, knees, scalp, and back.[12][13]

• Plaques of psoriasis
• A person's arm covered with plaque psoriasis
• Psoriasis of the palms
• Psoriasis of the scalp
• Psoriasis on a leg

Other forms

Additional psoriasis types comprise about 10% of cases. They include pustular, inverse, napkin, guttate, oral, and seborrheic-like forms.[14]

Pustular psoriasis appears as raised bumps filled with noninfectious pus (pustules).[15] The skin under and surrounding the pustules is red and tender.[16] Pustular psoriasis can either be localized or more widespread throughout the body. Two types of localized pustular psoriasis include psoriasis pustulosa palmoplantaris and acrodermatitis continua of Hallopeau; both forms are localized to the hands and feet.[17]

Inverse psoriasis (also known as flexural psoriasis) appears as smooth, inflamed patches of skin. The patches frequently affect skin folds, particularly around the genitals (between the thigh and groin), the armpits, in the skin folds of an overweight abdomen (known as panniculus), between the buttocks in the intergluteal cleft, and under the breasts in the inframammary fold. Heat, trauma, and infection are thought to play a role in the development of this atypical form of psoriasis.[18]

Napkin psoriasis is a subtype of psoriasis common in infants under the age of two and is characterized by red papules with silver scales in the diaper area that may extend to the torso or limbs.[19][20] Napkin psoriasis is often misdiagnosed as napkin dermatitis (diaper rash).[21] It typically improves as children age and may later present in more common forms as plaque psoriasis or inverse psoriasis.[22]