Psoriasis presents as well defined erythematous plaques covered with silvery scales commonly over the scalp, extremity, particularly over knees and elbows and lumbosacral region.
Psoriatic plaque is A well circumscribed area differing from the surrounding surface. These areas are red, or purple, with white scales on top. Red patches are dry, itchy and scaly.
Psoriasis varies in severity from small, localized patches to complete body coverage.
There are five main types of psoriasis: Plaque; Guttate; Inverse; Pustular and Erythrodermic.
But most common type is Plaque Psoriasis, also known as Psoriasis Vulgaris, which makes up about 90 % of cases.
Fingernails and toenails are affected in most people with psoriasis at some point in time.
Any injury to the skin in patients with psoriasis, induces lesions of psoriasis at that site, which is called Koebner phenomenon.
The disorder can also affect the joints and eyes. The eye is involved in about 10% of patients, mostly women.
Psoriasis is generally thought to be a genetic disease that is triggered by environmental factors.
The exact etiology is unknown, but it is considered to be an autoimmune disease mediated by T lymphocytes. The pathophysiology of psoriasis involves infiltration of the skin by activated T cells which stimulate proliferation of keratinocytes. This dysregulation in keratinocyte turnover results in the formation of thick plaques. Other associated features include epidermal hyperplasia and parakeratosis.
Injury in the form of mechanical, chemical, and radiational trauma induces lesions of psoriasis.
In addition, the epidermal cells fail to secrete lipids which results in flaky and scaly skin, which is typical of psoriasis.
On successive removal of psoriatic scales pinpoint bleeding points are seen. This is called Auspitz sign which is used to confirm the diagnosis clinically.
Usually, diagnosis is made by clinical morphology and site of lesions. Histopathology is rarely necessary but may help to differentiate psoriasis from another dermatosis if the diagnosis is not easy.
In the United States, about 2% of the population is affected by psoriasis.
The prevalence of psoriasis is low in Japan and may be absent in Aboriginal Australians and Indians from South America.
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