Psoriasis Resource Center
Plaque psoriasis is the most common form of psoriasis. Some studies have found that between 55% and 60% of physician-diagnosed psoriasis cases are plaque psoriasis. Other sources say the proportion is even greater and put it at between 80% and 90%. Plaque psoriasis is characterized by well-defined, raised erythematous plaques. In people with dark skin, post-inflammatory hyperpigmentation may be a feature. The plaques tend to be roughly round or oval in shape and are typically located on the scalp, trunk, gluteal cleft, and the extensor surfaces of the elbows and knees. A dry, silvery scale is often present, creating a whitish-pink appearance. Bathing or moisturizers may reduce the appearance of the scale. Fissures within the plaques can be painful.
Guttate psoriasis is characterized by small (usually less than 1 centimeter in diameter) plaque and papules that are salmon-pink in color. Guttate means droplike, and the plaques and papules have that appearance. Guttate psoriasis usually affects children and young adults and comes on suddenly.
Pustular psoriasis can be localized or generalized. The acute generalized version is called the von Zumbusch variant and may be accompanied by myriad problems: fever, diarrhea, leukocytosis, and hypocalcemia. Some cases also lead to kidney, liver, and respiratory abnormalities.
Erythrodermic psoriasis is characterized by generalized erythema that covers the entire body surface area with various amounts of scaling. It can develop gradually from plaque psoriasis or come on suddenly. The risk of infection is high, and inpatient management is often necessary.
Inverse psoriasis is called inverse because the areas of the skin affected are, in some sense, the reverse of the extensor surfaces of the elbows and knees that are commonly affected by plaque psoriasis. Common locations of inverse psoriasis include the axillary, genital, and inframammary regions. Because those areas tend to trap moisture, the plaque tends to be erythematous without scaling. Sometimes inverse psoriasis is misdiagnosed as a bacterial or fungal skin infection because of the lack of the telltale psoriatic scaling.
Nail psoriasis can occur in all the various types of psoriasis. The fingernails are affected more often than the toenails. Nail psoriasis can occur before any area of the skin is affected but also at the same time as cutaneous psoriasis. It is common in people with psoriatric arthritis and may predict its onset and contribute to its diagnosis. Nail psoriasis may present as tiny pits, red spots on the lunula, or a crumbling of the nail plate. When the nail bed is affected, brown spots may occur. Dermatologists refer to that manifestation as the “oil-drop sign” because of the resemblance to drops of motor oil.
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