Health Tips

Pityriasis rubra pilaris (PRP) is a rare skin disorder with a mouthful name, but it can be often confused with other more common skin disorders such as eczema and psoriasis due to their similarities. 

Features of PRP

PRP has the following distinguishable features:

• Scaly patches (known as plaques) can be seen on skin (hence the word ‘pityriasis’). It’s also common to find thickened and yellowish skin on the palms and soles, known as palmoplantar keratoderma. This is why PRP is often mistaken for psoriasis because the latter may also lead to similar symptoms.

• Long-term inflammation of the skin, which causes the plaques to look orange-red (hence the word ‘rubra’).

• Rough, dry plugs can be felt within the patches and are due to clogged hair follicles  (hence the word ‘pilaris’), often most obvious on the backs of the fingers. 

• The plaques may first occur on only some parts of the body, such as elbows, knees, ankles, palms and soles. The areas which are not affected look like patches of normal skin existing between lesions (called ‘islands of sparing’). This causes the skin colors to look uneven, known as irregular hyperpigmentation.

• However, as time goes by, PRP may eventually spread over the whole body, leading to what’s called erythroderma. 

• The plaques may feel itchy, especially during the early stage of disease.

Still don’t get it? Let’s see some pictures:

Image credit: DermNetNZ via CC BY-NC-ND 3.0 NZ

Image credit: DermNetNZ via CC BY-NC-ND 3.0 NZ

Image credit: DermNetNZ via CC BY-NC-ND 3.0 NZ

Image via JAMA Dermatology Patient Page - Pityriasis Rubra Pilaris

Causes of PRP

Unfortunately, the exact causes of PRP is unknown. But we do know that PRP affects individuals of all racial backgrounds and appears to affect both genders equally. Scientists are still investigating how PRP came about, but so far they have proposed that PRP seems to be closely associated with two players in our immune system: tumor necrosis factor (TNF)-alpha and interleukin (IL)-23-Th17 axis. It’s okay if these terms don’t ring a bell to you; just know that it might have something to do with our immune system. More studies are required to learn the exact causes of PRP.

Besides that, scientists also think that PRP might be caused by the following reasons:

1. Abnormal vitamin A metabolism — Noticed the small, scaly bumps in PRP? It’s very similar to a condition called phrynoderma, a condition caused by the lack of vitamin A. However, scientific evidence on this front has not been very substantial, so the roles of vitamin A in PRP still remains unclear.

2. Infection — Several case reports have documented the development of PRP in individuals after streptococcal and viral infections, as well as the coexistence of human immunodeficiency virus (HIV) infection and PRP. Particularly, scientists noticed the improvement of PRP after HIV patients receive antiretroviral treatment for HIV. 

3. Genetics — Genetic factors play a role in at least some cases of PRP. The mutations in a gene called CARD14 gene seems to be associated with PRP.

How is PRP diagnosed?

PRP can be challenging to diagnose, and no blood tests are available to confirm the disease. The diagnosis is made by examination of the skin and nails by a doctor or nurse.  A skin biopsy is not necessary, but may be done to exclude other causes of skin diseases. Skin biopsy is where a small piece of skin is removed under a local anaesthetic and examined under a microscope. A referral to a skin specialist may be made by the doctor to confirm a diagnosis. 

Treatment of PRP

Unlike many other diseases, there’s no consensus on treatment among the medical community. Treatment of PRP is largely based upon the clinical experience of the doctor, and because no controlled trials have been performed, there is uncertainty regarding the true efficacy of individual treatments. 

Generally, PRP can be treated with a combination of topical preparations (creams or ointments to be applied on skin) and oral medications:

Topical preparations

• Steroid creams and/or ointments — This can improve the inflammation and scaling of skin, but do not change the duration of rash. 

• Keratolytics — An example is salicylic acid. Keratolytics work by removing thickened, dead cells and unclog pores.

• Topical calcipotriol (an vitamin D derivative)

• Topical tretinoin (an vitamin A derivative)

• Emollients — Also known as moisturizers. Emollients are a very important part of treatment to help moisten dry skin and restore the barrier function of the skin. The emollient should be applied liberally and regularly.

Note: Emollients, creams, lotions and ointments contain oils which can make it easier for dressings, clothing, bed linen or hair to catch fire. To reduce the fire risk, patients using these moisturising products are advised to be very careful near naked flames to reduce the risk of clothing, hair or bedding catching fire. In particular, smoking cigarettes should be avoided and being near people who are smoking or using naked flames, especially in bed. Candles may also risk fire. Daily washing is advisable for clothing which is in regular contact with emollients and bed linen.

Oral medications

Individuals with more severe PRP may require oral medications. The most common medications are:

• Retinoids — Based on limited case reports and many doctors’ clinical experience, retinoids are useful in treating most of the PRP cases. Examples of retinoids are medications called acitretin and isotretinoin. It may take three to six months for patients to start showing improvement after starting oral retinoids. 

• Methotrexate — For patients who are not responding to retinoids, doctors may prescribe methotrexate. Methotrexate is a type of medication that is also commonly used in other autoimmune diseases and in some cancers. 

In severe cases of PRP, both retinoids and methotrexate may be given together.

Biologics injectables

• Biologics — Biologic medications are injectable treatments that are becoming more popular when all the above have failed to work and the condition persists. Biologic medications work on the antibodies blocking a certain protein involved in causing PRP. These include infliximab, ustekinumab, secukinumab and adalimumab.

A word from Doc2Us

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References

1. MSD Manual - Pityriasis Rubra Pilaris

2. UpToDate - Pityriasis rubra pilaris

3. DermNetNZ - Pityriasis rubra pilaris

4. British Association of Dermatologists - PITYRIASIS RUBRA PILARIS (PILs) 

Cover image credit: DermNetNZ via CC BY-NC-ND 3.0 NZ

Written by

Ms Joyce Toh