Pityriasis rubra pilaris
Pityriasis rubra pilaris is a mildly itchy chronic skin disorder that is possibly caused by an inherited metabolic defect. Initially, the disorder is characterized by elevated spots (papules) on the skin. These spots grow and become connected, producing red plaques over large areas. Pityriasis rubra pilaris is a rare erythematosquamous cutaneous eruption with characteristic follicular papules that is associated with abnormal metabolism of vitamin A (resulting in low levels). Pityriasis rubra pilaris (PRP) is the name given to a group of rare skin disorders that present with reddish-orange coloured scaling patches with well defined borders. They may cover the entire body or just parts of the body such as the elbows and knees, palms and soles.
Often there are areas of uninvolved skin, particularly on the trunk and limbs, which are referred to as islands of sparing. The palms and soles are usually involved and become diffusely thickened and yellowish (palmoplantar keratoderma). PRP is often initially mistaken for another skin condition, usually psoriasis. Classical adult-onset PRP most often starts on the head, neck and upper trunk as a red scaly rash. Often there is a solitary lesion but within a few weeks multiple patches appear and they join together to form groups of reddish-orange lesions. Over a few weeks these spread downwards and may cover most of the body (erythroderma). Rough, dry plugs can be felt within the patches and are due to plugged hair follicles, often most obvious on the backs of the fingers. Patients may also complain of itching in the early stages of the disease. The palms and soles become thickened and yellow coloured. Cracks may develop which can be painful and make walking and using the hands difficult. The nails may become thickened and discoloured at the free nail edge and may show linear black streaks (splinter haemorrhages). The hair may thin considerably.
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 value of treatment is difficult to assess, as the clinical course is so variable for each of the different types of PRP. In general, the inherited forms of PRP tend to persist throughout life whilst the sporadically acquired forms tend to resolve spontaneously eventually.
Topical medications such as emollients may be used to relieve symptoms of dryness and cracking. In severe cases acitretin or isotretinoin may be useful. Methotrexate has been of limited value. 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.