Psoriasis Area Severity Index
Encyclopedia
Psoriasis Area and Severity Index (PASI) is the most widely used tool for the measurement of severity of psoriasis
. PASI combines the assessment of the severity of lesion
s and the area affected into a single score in the range 0 (no disease) to 72 (maximal disease).
(H) (10% of a person's skin
); arm
s (A) (20%); trunk
(T) (30%); leg
s (L) (40%)). Each of these areas is scored by itself, and then the four scores are combined into the final PASI. For each section, the percent of area of skin involved, is estimated and then transformed into a grade from 0 to 6:
Within each area, the severity is estimated by three clinical signs: erythema
(redness), induration (thickness) and desquamation
(scaling). Severity parameters are measured on a scale of 0 to 4, from none to maximum.
The sum of all three severity parameters is than calculated for each section of skin, multiplied by the area score for that area and multiplied by weight of respective section (0.1 for head, 0.2 for arms, 0.3 for body and 0.4 for legs).
assessment and severity
assessments were found to be non-reproducible. Several automated procedure for more reproducible measurement of psoriatic area were developed, but were not suitable for large-scale trials
. A method where the advantage of accurate computerized measurement of the area on the digital photograph was combined with physician's proficiency in determination of the edge of psoriatic lesion was published recently. The patients were examined and photographed before and after the therapy with calcipotriol ointment or placebo. The psoriatic area was manually outlined on the patient's photographs by physician and the area was automatically measured by a computer. For comparison, the physicians also made standard prosiatic area assessment. Computer-aided measurement of psoriatic lesion area was found to improve the power of the clinical trial, compared to the standard approach. The physician's estimations of the psoriatic lesion area tend to overestimate. The adapted PASI index, where the psoriatic area was not converted into an area grade, but was maintained as a continuous variable, also improved the power of the clinical trial. The modified PASI which involves computer-aided area measurement as a continuous variable is named Computer aided psoriasis continuous area and severity score cPcASI.
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...
. PASI combines the assessment of the severity of lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s and the area affected into a single score in the range 0 (no disease) to 72 (maximal disease).
Calculation
The body is divided into four sections (headHuman head
In human anatomy, the head is the upper portion of the human body. It supports the face and is maintained by the skull, which itself encloses the brain.-Cultural importance:...
(H) (10% of a person's skin
Human skin
The human skin is the outer covering of the body. In humans, it is the largest organ of the integumentary system. The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to that of most other mammals,...
); arm
Arm
In human anatomy, the arm is the part of the upper limb between the shoulder and the elbow joints. In other animals, the term arm can also be used for analogous structures, such as one of the paired forelimbs of a four-legged animal or the arms of cephalopods...
s (A) (20%); trunk
Torso
Trunk or torso is an anatomical term for the central part of the many animal bodies from which extend the neck and limbs. The trunk includes the thorax and abdomen.-Major organs:...
(T) (30%); leg
Human leg
The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...
s (L) (40%)). Each of these areas is scored by itself, and then the four scores are combined into the final PASI. For each section, the percent of area of skin involved, is estimated and then transformed into a grade from 0 to 6:
- 0% of involved area, grade: 0
- < 10% of involved area, grade: 1
- 10-29% of involved area, grade: 2
- 30-49% of involved area, grade: 3
- 50-69% of involved area, grade: 4
- 70-89% of involved area, grade: 5
- 90-100% of involved area, grade: 6
Within each area, the severity is estimated by three clinical signs: erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
(redness), induration (thickness) and desquamation
Desquamation
Desquamation , also called skin peeling, is the shedding of the outermost membrane or layer of a tissue, such as the skin.-Skin:Normal, nonpathologic desquamation of the skin occurs when keratinocytes, after moving apically over about 14 days, are individually shed unnoticeably...
(scaling). Severity parameters are measured on a scale of 0 to 4, from none to maximum.
The sum of all three severity parameters is than calculated for each section of skin, multiplied by the area score for that area and multiplied by weight of respective section (0.1 for head, 0.2 for arms, 0.3 for body and 0.4 for legs).
Objectivisation
Psoriatic areaArea
Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...
assessment and severity
Severity
Severity may refer to:* Severity , a canceled video game* a dimension for classifying seriousness for Technical support issues...
assessments were found to be non-reproducible. Several automated procedure for more reproducible measurement of psoriatic area were developed, but were not suitable for large-scale trials
Clinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...
. A method where the advantage of accurate computerized measurement of the area on the digital photograph was combined with physician's proficiency in determination of the edge of psoriatic lesion was published recently. The patients were examined and photographed before and after the therapy with calcipotriol ointment or placebo. The psoriatic area was manually outlined on the patient's photographs by physician and the area was automatically measured by a computer. For comparison, the physicians also made standard prosiatic area assessment. Computer-aided measurement of psoriatic lesion area was found to improve the power of the clinical trial, compared to the standard approach. The physician's estimations of the psoriatic lesion area tend to overestimate. The adapted PASI index, where the psoriatic area was not converted into an area grade, but was maintained as a continuous variable, also improved the power of the clinical trial. The modified PASI which involves computer-aided area measurement as a continuous variable is named Computer aided psoriasis continuous area and severity score cPcASI.