Pityriasis rubra pilaris (PRP) is a rare condition that is often initially mistaken for another skin disorder, usually psoriasis. PRP is not really a single condition, but rather a group of unusual eruptions that cause red scaly patches containing dry plugged pores. It may cover the entire body, or just the elbows and knees.
PRP mostly affects adults over 40, but some children are also affected. The cause of PRP is unknown. Sometimes minor burns rashes and infections seem to trigger it. There is no blood test for PRP. It is usually diagnosed when a dermatologist, suspecting the condition, does a biopsy and specifically asks it to be checked for PRP. Sometimes PRP is suspected only after the usual creams, pills and even ultraviolet light treatments used for skin conditions have no effect.
PRP most often starts as a patchy rash on the scalp, face or chest. Over a period as short a several weeks it extends downward, and often covers much of the body. It spares areas of old scars and injuries, and leaves small islands of entirely unaffected skin. The rash has an orange-red color ("salmon") and the palms and soles become thickened. Rough, dry plugs can be felt within the rash. The itching is usually severe at first, and then later is not as bad as you would think considering how bad the rash looks.
The best treatment is Accutane or Soriatane pills. These are closely related "retinoid" medications. While these have many minor side effects, they do not usually cause any serious harm to the body. A more potent and more effective treatment is methotrexate tablets, but as these can have dangerous side effects they are saved for people who don't improve with the retinoids. Methotrexate may put the PRP into remission, so it goes away and stays away.
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