Psoriasis (/sɵˈraɪ.əsɨs/; from Greek ψωρίασις, meaning “itching condition” or “being itchy”, from psora, “itch” and -sis, “action, condition”; also termed psoriasis vulgaris), is a common, chronic, relapsing/remitting, immune-mediated skin disease characterized by red, scaly patches, papules, and plaques, which usually itch. The skin lesions seen in psoriasis may vary in severity from minor localized patches to complete body coverage. The disease affects 2–4% of the general population.
The five main types of psoriasis are plaque, guttate, inverse, pustular, and erythrodermic. 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 andknees, 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.
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. 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. Oxidative stress, stress, and withdrawal of a systemic corticosteroid have each been suggested as a trigger for psoriasis. Injury to the skin can trigger local psoriatic skin changes known as the Koebner phenomenon.
No cure is available for psoriasis, but various treatments can help to control the symptoms.Though many treatments are available, psoriasis can be difficult to treat due to its chronic recurrent nature. The effectiveness and safety of a new generation of targeted immune therapies is being established with randomized controlled trials, and several have been approved (or rejected for safety concerns) by regulatory authorities.
Additional types of psoriasis affecting the skin include inverse psoriasis, guttate psoriasis, oral psoriasis, and seborrheic-like psoriasis
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.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.Napkin psoriasis is often misdiagnosed as napkin dermatitis.
Guttate psoriasis is characterized by numerous small, scaly, red or pink, teardrop-shaped lesions (papules). These numerous spots of psoriasis appear over large areas of the body, primarily the trunk, but also the limbs and scalp. Guttate psoriasis is often triggered by a streptococcal infection, typically streptococcal pharyngitis.The reverse is not true.
Oral psoriasis is very rare, in contrast to lichen planus, another common papulosquamous disorder that commonly involves both the skin and mouth. When psoriasis involves the oral mucosa (the lining of the mouth), it may be asymptomatic, but it may appear as white or grey-yellow plaques. Fissured tongue is the most common finding in those with oral psoriasis and has been reported to occur in 6.5-20% of people with psoriasis affecting the skin. The microscopic appearance of oral mucosa affected by geographic tongue (migratory stomatitis) is very similar to the appearance of psoriasis. However, modern studies have failed to demonstrate any link between the two conditions.