How is the severity of psoriasis assessed?

The psoriasis is a systemic and chronic inflammatory skin condition. It presents itself as red and thick plaques that shed. Psoriasis is explained by an excessive renewal and accumulation of epidermal cells, leading to a local inflammation. This disease tends to affect adults, with a peak onset generally between 20 and 40 years of age.

Histological analyses reveal an increase in the thickness of the epidermis (acanthosis) and incomplete differentiation of keratinocytes (parakeratosis). Its manifestation is triggered by the combination of several risk factors. These include the immune system, the genetic predisposition and environmental factors. The skin symptoms of psoriasis can affect any area of the body, from the ears to the tongue, including the genital areas.

The scores commonly used to assess the severity of psoriasis are the DLQI (Dermatology Life Quality Index), the BSA (Body Surface Area) and the PASI (Psoriasis Area and Severity Index).

The DLQI (Dermatology Life Quality Index).

The psoriatic condition of a patient can be assessed using the DLQI score. This score explores aspects of the patient's life that may be disrupted by psoriasis. A 10-question questionnaire, following a scale from 0 (not at all) to 3 (a lot), is given to the patient. The questions focus on how psoriasis impacts daily life over the past seven days. They explore both professional and personal life as well as daily activities, clothing or even the treatments. The result gives a score from 0 to 30. The highest total score reflects a severe impact of psoriasis on the quality of life.

The BSA (Body Surface Area Index, Affected Body Surface).

The BSA is a score that indicates the percentage of the epidermis affected by psoriasis. To calculate it, the surface of the hand must correspond to 1% of the total body surface. The specialist then assesses the number of "hands" corresponding to the surface of the lesions. Psoriasis is considered severe if more than 10% of the body surface is affected. However, the BSA does not take into account the location of the lesions, which is an indicator of the severity of the condition. Indeed, a limited psoriasis of the hands and face is harder to bear than an extensive psoriasis of the back.

The PASI (Psoriasis Area and Severity Index, Index of Psoriasis Severity).

The PASI score takes into account the area of the epidermis affected, the thickening of the skin, the extent of the plaques, the scaling as well as the degree of redness. A mathematical formula ultimately gives a score ranging from 0 (mild form) to 72 (severe form).

The PASI score is calculated by assigning a value from 0 (absence of symptoms) to 4 (severe symptoms) to the four previous parameters in the following anatomical regions: head, trunk, arms, and legs. The body surface is divided into percentages, where each anatomical region represents a certain percentage of the total body.

Next, each previously defined score is multiplied by a body surface area coefficient corresponding to each anatomical region. The sum of these scores is then calculated to obtain the PASI score. Generally, a PASI score less than 10 is considered mild, while a score between 10 and 20 is considered moderate, and a score above 20 is regarded as severe.

• FLEISCHER A. B. Patient measurement of psoriasis disease severity with a structured instrument. Journal of Investigative Dermatology (1994).

• Le diagnostic. Association France Psoriasis (2016).

• LILUASHVILI S. & al. Dermatology life quality index and disease coping strategies in psoriasis patients. Postepy Dermatologii (2019).