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How Do Doctors Determine Severity And Type of Psoriasis?

Reviewed by: HU Medical Review Board | Last reviewed: July 2016.

Plaque psoriasis is a chronic skin disease that causes patches of a person’s skin to become inflamed, thickened, and covered in silvery scales. These patches can often be painful and itchy. When a person is first diagnosed with psoriasis or is experiencing a flare up of symptoms, healthcare providers will work with the person to assess the current level of psoriasis severity. This will enable the healthcare provider and person living with psoriasis to figure out the best possible treatment plan.

Plaque psoriasis is generally classified into three categories: mild, moderate, or severe. Approximately 80% of people diagnosed with psoriasis have mild to moderate disease, and 20% are diagnosed with severe psoriasis.

How is the severity of psoriasis assessed?

Healthcare providers assess the severity of a patient’s psoriasis based on two types of information:1,2,5

Both of these types of information are very important to making an accurate assessment of severity. The answer to the first question, about how much of the body is affected by patches of psoriasis, is also known as the affected “body surface area” (BSA). The answer to the second question is used to help the healthcare provider understand the social and emotional impact that psoriasis can have on a person in their daily life.

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How is the affected body surface area measured?

To measure the amount of body surface area affected by plaque psoriasis, healthcare providers work with a patient to help estimate the percentage of the person’s body that is affected. The reference point they use is that 1% of a person’s total body area is roughly equal to the size of the person’s hand (from the wrist to the tips of the fingers, with the fingers together and the thumb tucked in)1.

In terms of affected body surface area2:

  • Mild psoriasis affects an area that is less than 3% of the person’s total body surface
  • Moderate psoriasis affects an area that is between 3% and 10% of the person’s total body surface
  • Severe psoriasis affects 10% or more of the person’s total body surface

How is the effect of psoriasis on a person’s quality of life measured?

Living with psoriasis can be difficult for many people because it can affect so many aspects of a person’s life beyond the physical pain and discomfort that condition can cause. People with psoriasis may feel self-conscious about the appearance of their skin, particularly if they have large affected areas and/or patches of plaques in publically visible areas. An assessment of psoriasis severity that only takes into account only the size of the affected area does not tell the whole story, however. For example, some people may have relatively small affected patches on their hands and feet which greatly affect their ability to work and take part in activities they enjoy. This is why healthcare providers will also use tools to help understand the overall effect of psoriasis on the patient’s quality of life.2

How can we measure the impact?

To measure the impact of the disease on a person’s quality of life, healthcare providers will talk with the patient to gain an understanding of the various ways that having psoriasis affects the patient’s day-to-day life on multiple levels: social, emotional, professional, financial, and so on3.

To help guide the discussion, the healthcare provider may ask the patient to complete a questionnaire, such as the Dermatology Quality of Life Index (DLQI)5. These kinds of questionnaires include questions such as:

  • “Over the last week, how embarrassed or self-conscious have you been because of your skin?”
  • “Over the last week, how much has your skin interfered with you going shopping or looking after your home or garden?”
  • “Over the last week, how much has your skin affected work or, any social or leisure activities?”
  • “Over the last week, how much has your skin created problems with your partner or any of your close friends or relatives?”

Every patient’s experience of living with psoriasis is unique, and a patient’s psoriasis severity will likely change over time.

Healthcare providers use information from the answers to these types of questions combined with a physical assessment of the patient’s affected body surface area to work toward the best possible treatment plan to help the patient to control the disease and manage its symptoms.

What are the types of psoriasis?

Plaque psoriasis is the most common type of psoriasis, affecting at least 80% of people who have this autoimmune disorder.

There are also other types of psoriasis that are less common yet affect people around the world. It is possible for someone to have plaque psoriasis and also be diagnosed with other types of psoriasis over the course of their lifetime and to have more than one type at a time. The other types of psoriasis are: