In psoriasis, the keratinocytes in the epidermis undergo excessive proliferation. This causes the epidermis to thicken in a process called acanthosis.
Psoriasis usually presents as well demarcated plaques described as having a salmon color. A plaque is a general dermatology term for an area of skin elevation > 1 cm in diameter.
Classically, silver colored scales overlie the psoriatic plaques. The silver scale is caused by hyperkeratosis or excessive keratin in the stratum corneum.
Psoriasis tends to favor the extensor surfaces including the knees and elbows. It also often occurs on the scalp.
If the psoriatic plaque is scratched or removed, patients display pinpoint bleeding at the site. This is a phenomenon known as Auspitz sign.
Auspitz Sign refers to pinpoint bleeding from exposed dermal papillae (which are rich in blood vessels) when psoriatic scales are picked off.
Patients experience itching, which can range from mild to severe.
Patients with psoriasis may experience nail changes including pitted nails, which are pinhead-sized depressions in the nail bed. Additionally, patients can experience changes in the nail color as well as separation of the nail from the nail bed.
Histologically, there are collections of neutrophils in the stratum corneum of the epidermis, termed Munro microabscesses.
Histological findings of psoriasis include parakeratosis, which is retained keratinocyte nuclei in the thickened stratum corneum. Recall, the stratum corneum is the most superficial layer in the epidermis and is normally characterized by keratin in anucleate cells. It is also important to note that there is histologic absence of the stratum granulosum in psoriasis.
Systemic retinoids (derivatives of Vitamin A) are used in patients with moderate to severe psoriasis. Retinoids may be used in combination with UV light therapy.
Patients with mild to moderate psoriasis typically respond well to topical treatments. Topical corticosteroids are the mainstay of topical psoriasis treatment and exert anti-inflammatory, anti-proliferative and immunosuppressive actions.
Tar is helpful as an adjunct to topical corticosteroids. Tar products are available in the form of shampoos, creams, lotions, ointments and oils.
Moderate to severe psoriasis often requires the usage of systemic therapies including immunosuppressive or immunomodulatory drugs such as methotrexate, cyclosporine or tacrolimus.
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