How Severe Is My Psoriasis?

Using PASI scores to characterize disease severity

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Psoriasis is not one disease. Not only are there different types of psoriasis, but there are also different symptoms and degrees of severity. When psoriasis is diagnosed, it is important to characterize all of these things to ensure that the disease is appropriately treated. As much as you may want to alleviate the symptoms, you don't want to be overtreated and suffer side effects.

To determine the severity of your psoriasis, the dermatologist or rheumatologist will assess three things: the percentage of skin affected, the characteristics of the lesions (referred to as plaques), and the impact of the disease on your daily life.

General Definitions

Arguably, the most important factor in assessing the severity of psoriasis is the amount of skin involved. This will not only direct which types of treatment are appropriate, but it can also provide insights into the emotional impact of the disease. In the simplest possible terms, the more skin involved, the greater the physical and emotional impact.

To this end, many doctors will base the severity of psoriasis on the body surface area (BSA) of skin affected, denoted by percentages. (By way of reference, a hand has a BSA of roughly 1 percent.)

Based on the BSA, the severity can be broadly classified as follows:

  • Mild psoriasis means that less than 3 percent of the body is affected.
  • Moderate psoriasis is when 3 percent to 10 percent of skin is affected.
  • Severe psoriasis is when over 10 percent of the body is affected.

As straightforward as this system is, it has its limitation. This is especially true when the disease hovers between "mild" and "moderate" or "moderate" and "severe." While is possible to use clinical judgment to direct treatment, most specialists prefer a more insightful approach to diagnosis.

PASI Scores

To many specialists, using BSA as the sole determinant of disease severity is akin to looking at psoriasis through a peephole. It allows for a wide range of interpretations based on the broadest of measurements. For example:

  • Might someone with 3 percent of affected skin be treated the same as someone with 10 percent even though they both have "moderate" psoriasis?
  • What if there is a lot of affected skin with only mild flaking or a smaller area of skin with cracking and bleeding?
  • How might the decision be affected if the plaques are on the face versus those hidden under a sleeve on your forearm?

In the end, all of these concerns should factor into the clinical decision It is for this reason that a tool called the Psoriasis Area and Severity Index (PASI) was created. PASI uses BSA and plaque characteristics to render a more qualified assessment of the disease severity.

This is done in two steps:

Step 1: Scoring the BSA

The calculations used in a PASI survey are broken down into four body parts:

  • Head (total BSA of 10 percent)
  • Trunk (total BSA for 30 percent)
  • Arms (total BSA of 20 percent)
  • Legs (total BSA of 40 percent)

A score of 0 to 6 is assigned for the percentage of skin involved in each of the four body parts (for a maximum score of 24):

  • 0: 0 percent involvement
  • 1: less than 10 percent involvement
  • 2: 10 to 29 percent involvement
  • 3: 30 to 49 percent involvement
  • 4: 50 to 69 percent involvement
  • 5: 70 to 89 percent involvement
  • 6: 90 to 100 percent involvement

Step 2: Calculating PASI

After the BSA score is tallied, the doctor will assess three different disease characteristics on each of the four body parts.

  • Erythema (redness)
  • Induration (thickness)
  • Desquamation (scaling)

Each of the symptoms is assigned a score of 0 to 4 for a maximum score of 12 per body part. This is then added to your BSA for the final PASI score.

While it is possible to get a maximum score of 72 (24 for the BSA plus 36 for the symptoms), there are rarely PASI scores of over 40.

Quality of Life

Generally speaking, a higher PASI score correlates to a lower quality of life. But, it's not always the case. The simple fact is that people respond to diseases differently, and psoriasis no exception. Even though two people may have the same PASI score, one might have a greater perception of pain and experience more emotional distress and social discomfort than the other.

To this end, some doctors will perform a subjective survey to quantify the impact of psoriasis on your day-to-day life. These may include:

  • Psoriasis Index of Quality of Life (PSORIQoL) which evaluates 25 different factors, including sleep, emotions, and social interactions
  • Psoriasis Life Stress Inventory (PLSI) which asks how stressful 18 daily tasks, like getting a haircut or going to public places, are for you to perform
  • Psoriasis Disability Index (PDI) which assesses how psoriasis affects your work, leisure time, and personal relationships

Clinical Value

By evaluating how psoriasis affects you physically and emotionally, your doctor can make a qualified decision regarding your treatment. With mild psoriasis, for example, your doctor may prescribe moisturizing creams and topical medications or recommend that you quit smoking or lose weight to reduce your risk of flares.

With moderate psoriasis, additional treatments may be incorporated, including immunosuppressant drugs like methotrexate or topical or oral retinoids. With severe psoriasis, additional interventions may be prescribed, including phototherapy and injectable biologic drugs like Humira (adalimumab) and Enbrel (etanercept).

Quality-of-life tests can also inform treatment decisions, particularly if the disease is causing anxiety or depression. In the end, the appropriate treatment of emotional symptoms is just as important as physical ones.

PASI scores, as well as the quality-of-life surveys, are also valuable in tracking your response to treatment. By keeping track of your condition, your doctor can ensure the optimal response to treatment and the optimal quality of life.

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