psoriasis psoriasis psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas 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. psoriasisback and arms of a person with psoriasispronunciation/səˈraɪəsɪs, ps-, sɒ-, sɔː-, soʊ-/ specialtydermatology (primarily); immunology, rheumatology and other specialties (e.g., cardiology and vascular medicine, nephrology, hepatology/gastroenterology, endocrinology, haematology) (indirectly/by association)symptomsred (purple on darker skin), itchy, scaly patches of skincomplicationspsoriatic arthritisusual onsetadulthooddurationlong-termcausesgenetic disease triggered by environmental factorsdiagnostic methodbased on symptomstreatmentsteroid creams, vitamin d3 cream, ultraviolet light, immunosuppressive drugs such as methotrexatefrequency79.7 million / 2–4% the five main types of psoriasis are plaque, guttate, inverse, pustular, and erythrodermic. plaque psoriasis, also known as psoriasis vulgaris, makes up about 90% of cases. it typically presents as red patches with white scales on top. areas of the body most commonly affected are the back of the forearms, shins, navel area, and scalp. guttate psoriasis has drop-shaped lesions. pustular psoriasis presents as small, noninfectious, pus-filled blisters. inverse psoriasis forms red patches in skin folds. erythrodermic psoriasis occurs when the rash becomes very widespread, and can develop from any of the other types. fingernails and toenails are affected in most people with psoriasis at some point in time. this may include pits in the nails or changes in nail color. psoriasis is generally thought to be a genetic disease that is triggered by environmental factors. 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. this suggests that genetic factors predispose to psoriasis. symptoms often worsen during winter and with certain medications, such as beta blockers or nsaids. infections and psychological stress can also play a role. the underlying mechanism involves the immune system reacting to skin cells. diagnosis is typically based on the signs and symptoms. there is no known cure for psoriasis, but various treatments can help control the symptoms. these treatments include steroid creams, vitamin d3 cream, ultraviolet light, immunosuppressive drugs, such as methotrexate, and biologic therapies targeting specific immunologic pathways. about 75% of skin involvement improves with creams alone. the disease affects 2–4% of the population. men and women are affected with equal frequency. the disease may begin at any age, but typically starts in adulthood. psoriasis is associated with an increased risk of psoriatic arthritis, lymphomas, cardiovascular disease, crohn's disease, and depression. psoriatic arthritis affects up to 30% of individuals with psoriasis. the word "psoriasis" is from greek ψωρίασις, meaning "itching condition" or "being itchy" from psora, "itch", and -iasis, "action, condition". signs and symptoms plaque psoriasis psoriatic plaque, showing a silvery center surrounded by a reddened border 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. 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. plaques of psoriasis a person's arm covered with plaque psoriasis psoriasis of the palms other forms additional types of psoriasis comprise about 10% of cases. they include pustular, inverse, napkin, guttate, oral, and seborrheic-like forms. pustular psoriasis severe generalized pustular psoriasis pustular psoriasis appears as raised bumps filled with noninfectious pus (pustules). the skin under and surrounding the pustules is red and tender. 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. inverse 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 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 (diaper rash). guttate psoriasis example of guttate psoriasis guttate psoriasis is an inflammatory condition characterized by numerous small, scaly, red or pink, droplet-like lesions (papules). these numerous papules appear over large areas of the body, primarily the trunk, limbs, and scalp, but typically spares the palms and soles. guttate psoriasis is often triggered by a streptococcal infection (oropharyngeal or perianal) and typically occurs 1–3 weeks post-infection. guttate psoriasis is most commonly seen in children and young adults and diagnosis is typically made based on history and clinical exam findings. skin biopsy can also be performed which typically shows a psoriasiform reaction pattern characterized by epidermal hyperplasia and rate ridge prolongation. there is no firm evidence regarding best management for guttate psoriasis; however, first line therapy for mild guttate psoriasis typically includes topical corticosteroids. phototherapy can be used for moderate or severe guttate psoriasis. biologic treatments have not been well studied in the treatment of guttate psoriasis. guttate psoriasis has a greater prognosis than plaque psoriasis and typically resolves within 1–3 weeks; however, up to 40% of patients with guttate psoriasis eventually convert to plaque psoriasis. erythrodermic psoriasis psoriatic erythroderma (erythrodermic psoriasis) involves widespread inflammation and exfoliation of the skin over most of the body surface, often involving greater than 90% of the body surface area. it may be accompanied by severe dryness, itching, swelling, and pain. it can develop from any type of psoriasis. it is often the result of an exacerbation of unstable plaque psoriasis, particularly following the abrupt withdrawal of systemic glucocorticoids. 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. mouth psoriasis in the mouth 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. seborrheic-like psoriasis seborrheic-like psoriasis is a common form of psoriasis with clinical aspects of psoriasis and seborrheic dermatitis, and it may be difficult to distinguish from the latter. this form of psoriasis typically manifests as red plaques with greasy scales in areas of higher sebum production such as the scalp, forehead, skin folds next to the nose, the skin surrounding the mouth, skin on the chest above the sternum, and in skin folds. psoriatic arthritis psoriatic arthritis is a form of chronic inflammatory arthritis that has a highly variable clinical presentation and frequently occurs in association with skin and nail psoriasis. it typically involves painful inflammation of the joints and surrounding connective tissue, and can occur in any joint, but most commonly affects the joints of the fingers and toes. this can result in a sausage-shaped swelling of the fingers and toes known as dactylitis. psoriatic arthritis can also affect the hips, knees, spine (spondylitis), and sacroiliac joint (sacroiliitis). about 30% of individuals with psoriasis will develop psoriatic arthritis. skin manifestations of psoriasis tend to occur before arthritic manifestations in about 75% of cases. nail changes psoriasis of a fingernail, with visible pitting a photograph showing the effects of psoriasis on the toenails psoriasis can affect the nails and produces a variety of changes in the appearance of fingers and toenails. nail psoriasis occurs in 40–45% of people with psoriasis affecting the skin, and has a lifetime incidence of 80–90% in those with psoriatic arthritis. these changes include pitting of the nails (pinhead-sized depressions in the nail is seen in 70% with nail psoriasis), whitening of the nail, small areas of bleeding from capillaries under the nail, yellow-reddish discoloration of the nails known as the oil drop or salmon spots, dryness, thickening of the skin under the nail (subungual hyperkeratosis), loosening and separation of the nail (onycholysis), and crumbling of the nail. medical signs in addition to the appearance and distribution of the rash, specific medical signs may be used by medical practitioners to assist with diagnosis. these may include auspitz's sign (pinpoint bleeding when scale is removed), koebner phenomenon (psoriatic skin lesions induced by trauma to the skin), and itching and pain localized to papules and plaques. causes the cause of psoriasis is not fully understood, but many theories exist. genetics