Doctors determine the severity of psoriasis using a medical survey called a Psoriasis Area and Severity Index Score, a PASI score for short. According to the Psoriasis and Psoriatic Alliance this score is most commonly used for treatment consideration and clinical trials, but is becoming more commonly used as a general scale to determine severity.
The assessment evaluates how much skin is covered by psoriasis and examines severity in terms of thickness, redness, and flakiness of the skin.
Your palm is considered 1 percent of your body. Typically the amount of body coverage by psoriasis is determined by how many palms can fit in that area. For example, if five palms can fit on your abdomen, that’s considered 5 percent body coverage. Surprisingly, Psoriasis Speaks states that mild psoriasis is considered 3 percent of the body being covered by psoriasis, 3 percent-10 percent is considered moderate, and anything greater than 10 percent is severe. You might think that it would take more than 10 percent to be considered severe.
The issue with this chart is it’s hard to determine severity from a mental standpoint for a patient. A person whose skin is affected by only 1 percent may still have a hard time mentally, socially, and emotionally just as much of a person who is covered by greater than 10 percent. The location of the disease can also make a difference. A person who has psoriasis on the bottom of the feet (which can affect the ability to walk) can suffer much more from pain than someone who may only have it on the hands.
Although the mental status can’t be determined, typically the medicine one should use can be decided depending on the location of the disease and how much of the body is covered. The PASI score assesses the following: head & neck, upper extremities (arms, hands), and lower extremities (legs, thighs, butt).
So based on body coverage, which medicine should a patient consider?
The scalp, head and neck is only considered a small amount of body, but can have a great effect on the emotional health of an individual as it is more difficult to cover these areas. Recently a psoriasis sufferer asked in a forum whether or not she should consider a biologic for her scalp psoriasis. Typically if the only area covered is anything above the neck, you would only use something topically.
Due to the side effects of other drugs and the minimal areas covered by psoriasis it is not worth the risk or cost to use drugs such as biologics and systemic. These drugs can run you thousands of dollars every month. Shampoos and steroid crèmes can be used in this area. There are also forms of phototherapy that are designed to specifically target the scalp.
The abdomen, upper and lower extremities make up a large amount of the body. Depending on the severity a doctor may prescribe just a topical, but if that does not work, oral meds or biologics may be considered. Typically, physicians will prescribe biologics for psoriasis patients with a PASI score greater than 10 percent.
Additionally, the National Psoriasis Foundation states that biologics and systematics are usually prescribed to patients who have failed under other treatments, so drugs that fail under those categories are usually the last resort of treatment.
Psoriasis and Psoriatic Arthritis Alliance
National Psoriasis Foundation