How Doctors Measure Psoriasis Severity

Patient Expert

Medical professionals generally use one of the following measures or surveys to categorize psoriasis as mild, moderate, or severe.

The Psoriasis Area and Severity Index, also known as PASI, is most common. PASI assesses four different areas of the body on a scale of zero to six, with zero meaning skin is clear and six meaning all the following areas are affected: head/neck, hand/arms, chest/abdomen/back, and buttocks/thighs/legs. Each region represents a certain percentage of the body. The head/neck is considered 10 percent, while the others are considered 20, 30, or 40 percent. The palm of the hand is considered 1 percent.

If more than 10 percent of the entire body is affected, the psoriasis is considered moderate to severe. The doctor then does some math to determine the actual score. This method is most frequently used in clinical trials to help measure the response rate of a treatment. When using PASI, an improvement of 50 to 75 percent is considered successful.

The Physician Global Assessment (PGA) is usually used in conjunction with PASI, but it also measures the appearance of the disease on a four-point scale. A score of zero means skin is clear and unaffected by disease, while a four indicates the most severe condition. This is the easier assessment to use in an evaluation.

Researchers from the National Psoriasis Foundation also created the NPF Psoriasis Score (NPF-PS). This assessment is unique in that it includes patient involvement, asking them about the level of itchiness of the skin.

Room for improvement

Although these assessments are a great start to better treatments, they still need improvement. For one thing, since there isn’t a single measure used by physicians across the board, it can create some disparities when it comes to reporting the results of clinical trials.

As a patient advocate, I have joined 10 other people living with psoriasis to collaborate with an organization called the International Dermatology Outcome Measures (IDEOM). This group of researchers and doctors is helping create a measure/survey that can be used in all clinical trials involving people living with psoriasis. It is our hope that using one main survey will help unify results in the clinical world, leading to more accurate decisions on treatment approvals.

This past year I went to an IDEOM meeting and learned about different drugs in the clinical-trial process. One medication in particular was not yet approved by the FDA, in part because some of the participants in the trial committed suicide. My issue with all the assessments currently being used is that hardly any of them evaluate the mental health of the subjects. So, were these people who committed suicide having mental-health issues before the study? Or was the suicide directly induced by the drug? Because this information was never assessed, we will never truly know.

The current surveys don’t do enough to evaluate all the conditions accompanying the disease. They don’t evaluate the mental component or the arthritis aspect. Although there are other measures which do, it is standard for researchers to only use one or two assessments during a clinical trial, so some factors will be missed. This is where surveys fall short; they measure one aspect of the disease but don’t encompass the entire spectrum.

See more helpful articles:

Pros and Cons of Clinical Trials for Psoriasis

Is Psoriasis Worse in Men?