Skill Checkup: A 27-Year-Old Woman With Erythematous Plaques on Her Elbow, Thighs, and Scalp

William James, MD


December 20, 2021

The National Psoriasis Foundation defines mild psoriasis as affecting less than 3% of BSA; 3%-10% of BSA involvement is considered moderate; and more than 10% of BSA involvement is considered severe. For most individuals, the palm of the hand is about the same size as 1% of the skin surface.

The severity of psoriasis is also measured by how psoriasis affects a person's quality of life. For example, a person with psoriasis on the scalp or in other areas that are readily visible (such as the hands) and cause embarrassment may be considered to have more severe psoriasis than cases in which psoriatic lesions can be covered easily.

Another measure of severity is the Psoriasis Area Severity Index (PASI), which assesses erythema, induration, and scaling plus the percentage of BSA affected, and provides a severity score ranging from 0 to 72. In general, a score of ≥ 10 is considered moderate to severe psoriasis. This measure is used infrequently in clinical practice and is more often used in clinical trials.

The Physician's Global Assessment (PGA) is a scoring system that accounts for erythema, induration, and scaling. It is suggested as an important measure to assess psoriasis severity and response to treatment. There are several different PGA versions, with most severity scores ranging from 0 to 4 or 0 to 5. In many clinical trials and research, the PGA is used as a primary endpoint, but its use in clinical practice, while potentially valuable, is infrequent.


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