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Diagnosis and Evaluation of Psoriasis

What Does Your Doctor Look for?


Updated September 16, 2011

Psoriasis is usually an easy thing for most dermatologists to diagnose. That is, it can typically be diagnosed on sight based on skin changes and the location of the condition on the body. No further testing is needed unless there is some confusion about the diagnosis. For example, a physician may find it more difficult to diagnose a patient who also has another condition, such as eczema. In these rare instances, a skin biopsy is usually easily able to make a specific diagnosis.

Just How Bad is it?

Somewhat more complicated than diagnosing psoriasis is evaluating how severe it is. How much of the body is covered? How severe is the rash in those areas? What is the effect on the patient's quality of life?

To answer these questions, objective measures have been developed to help compare one patient to another, or to assess a given patient's condition over time. More often than not, these more sophisticated measurements are used in clinical trials. However, they may be used in a doctor's office to justify a certain treatment for a patient, especially newer biologic agents, which can be very expensive. In these instances, insurance companies often require some sort of objective evidence that a patient's psoriasis is severe enough to warrant the expense of these drugs.

An Objective Measurement

The most commonly used "objective measure" is the Psoriasis Area Severity Index, also known as the PASI score. The body is divided into four areas -- head, trunk, upper extremities and lower extremities -- each of which carries a different weight based on the percentage of body surface they represent. Each area is assessed separately for the severity of psoriasis, specifically thickness, redness and scaliness. After a little bit of mathematics, a score is assigned from 0 to 72. Following this score over time is sometimes useful to assess a response to a particular treatment. More often, this is used during clinical trials of new treatments to prove effectiveness.

A Newer Way of Looking at Psoriasis Severity

A newer measurement called the Koo-Menter Psoriasis Instrument is a questionnaire that can be used to assess the effect that psoriasis has on a patient's overall quality of life. Insurance companies are now taking a closer look at this sort of subjective measure, since a patient with a relatively low PASI score may still have severe quality of life issues if the areas involved interfere with daily activities or have tremendous social implications (such as the face, hands or genitals). In these instances, the Koo-Menter Psoriasis Instrument may give a more accurate portrayal of the severity of a patient's psoriasis.


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