Psoriasis (//; from Greek , meaning "itching condition" or "being itchy",[1] from psora, "itch" and -sis, "action, condition"; also termed psoriasis vulgaris)[2] is a common, chronic, relapsing/remitting, immune-mediated systemic disease characterized by skin lesions including red, scaly patches, papules, and plaques, which usually itch.[2][3] The skin lesions seen in psoriasis may vary in severity from minor localized patches to complete body coverage.[2]

The five main types of psoriasis are plaque, guttate, inverse, pustular, and erythrodermic.[4] Plaque psoriasis, the most common form, typically manifests as red and white scaly patches on the top layer of the skin. Skin cells rapidly accumulate at these plaque sites and create a silvery-white appearance. Plaques frequently occur on the skin of the elbows and knees, but can affect any area, including the scalp, palms of hands, and soles of feet, and genitals. In contrast to eczema, psoriasis is more likely to be found on the outer side of the joint. Fingernails and toenails are frequently affected (psoriatic nail dystrophy) and can be seen as an isolated sign. Inflammation of the joints, known as psoriatic arthritis, affects up to 30% of individuals with psoriasis.[5]

The causes of psoriasis are not fully understood. It is not purely a skin disorder and can have a negative impact on many organ systems. Psoriasis has been associated with an increased risk of certain cancers, cardiovascular disease, and other immune-mediated disorders such as Crohn's disease and ulcerative colitis. It is generally considered a genetic disease, thought to be triggered or influenced by environmental factors.[2] Psoriasis develops when the immune system mistakes a normal skin cell for a pathogen, and sends out faulty signals that cause overproduction of new skin cells. It is not contagious.[6]Oxidative stress,[7]stress, and withdrawal of a systemic corticosteroid have each been suggested as a trigger for psoriasis.[8] Injury to the skin can trigger local psoriatic skin changes known as the Koebner phenomenon.[9]

No cure is available for psoriasis,[6] but various treatments can help to control the symptoms.[10][11] The effectiveness and safety of targeted immune therapies is being studied, and several have been approved (or rejected for safety concerns) by regulatory authorities. The disease affects 24% of the general population.[12]

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.[13] 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.[13][14]Psoriatic erythroderma (erythrodermic psoriasis) involves widespread inflammation and exfoliation of the skin over most of the body surface. It may be accompanied by severe itching, swelling and pain. It is often the result of an exacerbation of unstable plaque psoriasis, particularly following the abrupt withdrawal of systemic glucocorticoids.[15] This form of psoriasis can be fatal as the extreme inflammation and exfoliation disrupt the body's ability to regulate temperature and perform barrier functions.[16]

A person's arm covered with plaque psoriasis

Pustular psoriasis appears as raised bumps filled with noninfectious pus (pustules).[17] The skin under and surrounding the pustules is red and tender.[18] Pustular psoriasis can be localized, commonly to the hands and feet (palmoplantar pustulosis), or generalized with widespread patches occurring randomly on any part of the body. Acrodermatitis continua is a form of localized psoriasis limited to the fingers and toes that may spread to the hands and feet.[18]Pustulosis palmaris et plantaris is another form of localized pustular psoriasis similar to acrodermatitis continua with pustules erupting from red, tender, scaly skin found on the palms of the hands and the soles of the feet.[18]

Generalized pustular psoriasis (pustular psoriasis of von Zumbusch), also known as impetigo herpetiformis during pregnancy,[19] is a rare and severe form of psoriasis that may require hospitalization. The development of generalized pustular psoriasis is often caused by an infection, abrupt withdrawal of topical corticosteroid treatment, pregnancy, hypocalcemia, medications, or following an irritating topical treatment for plaque psoriasis.[18] This form of psoriasis is characterized by an acute onset of numerous pustules on top of tender red skin. This skin eruption is often accompanied by a fever, muscle aches, nausea, and an elevated white blood cell count.[18]Annular pustular psoriasis (APP), a rare form of generalized pustular psoriasis, is the most common type seen during childhood.[19] APP tends to occur in women more frequently than in men, and is usually less severe than other forms of generalized pustular psoriasis such as impetigo herpetiformis.[19] This form of psoriasis is characterized by ring-shaped plaques with pustules around the edges and yellow crusting.[19] APP most often affects the torso, neck, arms, and legs.[19]

Additional types of psoriasis affecting the skin include inverse psoriasis, guttate psoriasis, oral psoriasis, and seborrheic-like psoriasis.[20]

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.[21]Napkin psoriasis is a subtype of psoriasis common in infants characterized by red papules with silver scale in the diaper area that may extend to the torso or limbs.[22] Napkin psoriasis is often misdiagnosed as napkin dermatitis.[23]

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Psoriasis - Wikipedia, the free encyclopedia