Epidemiology and Classification of Psoriasis
Classification of Psoriasis
Unlike psoriatic arthritis, psoriasis has never had a generally accepted classification system. Discussions of the types of psoriasis generally fall into the extent, the clinical appearance and the location of the lesions. Thus, classification of psoriasis is descriptive rather than a systematic categorization that may be seen in the arthritic component of psoriatic disease.
Clinical Appearance of Lesions
The clinical description of psoriasis begins with the evaluation of the cardinal signs of the disease. These are erythema, the redness of lesions, induration, the thickness of lesions or how elevated a lesion may be when compared with surrounding normal skin and scaling. Thus, when describing psoriasis, clinicians will label lesions as small or large plaque, deeply or moderately erythematous, thick or thin plaque, or with thick or fine scale. Examples of these comparators can be found in Figure 2-1. It is critical to remember that despite numerous attempts to…
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Classification of Psoriasis
Unlike psoriatic arthritis, psoriasis has never had a generally accepted classification system. Discussions of the types of psoriasis generally fall into the extent, the clinical appearance and the location of the lesions. Thus, classification of psoriasis is descriptive rather than a systematic categorization that may be seen in the arthritic component of psoriatic disease.
Clinical Appearance of Lesions
The clinical description of psoriasis begins with the evaluation of the cardinal signs of the disease. These are erythema, the redness of lesions, induration, the thickness of lesions or how elevated a lesion may be when compared with surrounding normal skin and scaling. Thus, when describing psoriasis, clinicians will label lesions as small or large plaque, deeply or moderately erythematous, thick or thin plaque, or with thick or fine scale. Examples of these comparators can be found in Figure 2-1. It is critical to remember that despite numerous attempts to regularize these distinctions for research purposes, they remain subjective measures by the clinician.
The second descriptor is somewhat more objective but is still quite inexact. Psoriasis can be described by the extent of the body surface area (BSA) involved. There are a number of methods in evaluating BSA. The most commonly used is the palm measure, where the palm of the patient’s hand is about 1% of the BSA. Once the BSA is evaluated roughly, the patient can be classified by the extent of disease. A number of systems for this classification have been suggested over time, although none is consistently accepted. Mild, moderate and severe psoriasis have been described as under 3%, 3% to 10% and greater than 10%, respectively. Alternatively, less exact but possibly more clinically useful, psoriasis can be thought of as limited or extensive disease. The definitions here are purely utilitarian. Limited disease would be that amount over which a given patient could reasonably apply topical medication consistently while extensive disease is greater than this, highly subjective and individualized measure.
The final descriptors of psoriasis are the location of lesions. This evaluation of the location of lesions leads to the common “types” of psoriasis. Briefly, plaque psoriasis is the most common type that will cover most of the BSA including the scalp, trunk and extremities. These plaques can be found on the palms and soles and, in this case, are referred to as palmar/plantar psoriasis. Lesions that involve the moister areas of the skin, including the groin, axillae, face and genitals, are generally called areas of inverse psoriasis. While these “types” are sometimes thought to be distinct forms of the disease, it is critical to remember that they are based on location of lesions, not necessarily varieties of disease. Erythrodermic psoriasis, too, is based on the location of disease. In the case of erythroderma, the location is basically coverage of the entire body surface.
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