Pityriasis rubra pilaris (PRP): symptoms, types, diagnosis and treatment

Pityriasis rubra pilaris is a group of rare skin conditions. The Primary Care Dermatology Society (PCDS) describes it as characterised by orange-red erythema, scaly lesions and palmoplantar keratoderma, which means thickening of the skin of the palms and soles, and says it may be generalised or localised and may progress to erythroderma, widespread redness, with distinct areas of uninvolved skin. The BAD says it affects all races and sexes equally.

The cause is not known. The BAD says it is not an infection and is usually not hereditary, though there have been reports of families with multiple affected members. The PCDS notes that although most cases are sporadic, a familial form exists with an autosomal dominant inheritance pattern. PRP is also unrelated to hair-loss treatments that share the abbreviation PRP, which stands for platelet-rich plasma.

The BAD classifies PRP into six clinical types and the PCDS describes five. The differences reflect age at onset and pattern. The most useful distinction is between adult and juvenile forms and between classic and atypical presentations.

According to the BAD, PRP can look and feel different in different people. The rash may be itchy in its early stages. The skin on the palms and soles may become thick, and may split and become painful, so that walking may be difficult. Where the rash covers large areas, shivering, difficulty regulating temperature and fluid loss may occur.

In classic adult PRP, the BAD says the rash usually starts suddenly on the scalp and spreads to cover much of the chest and abdomen, with dry, scaly, red patches that have an orange tinge and well-defined edges. Smaller patches may join to cover large areas, and people sometimes become red all over (erythroderma). Areas of normal-looking skin between larger patches, called spared areas or islands of sparing, are characteristic. The hair follicles can feel rough because of follicle plugs, the palms and soles may be thickened and orange, and the nails may thicken, change colour and sometimes shed.

See a GP if you have a widespread scaly red rash that is not responding to creams, thick cracked skin on the palms and soles, or a rash that is spreading quickly. Because PRP is easily mistaken for psoriasis, referral to a dermatologist to confirm the diagnosis is common. The BAD says that referral to a skin specialist may be made to confirm the diagnosis.

If the rash covers most of your body, you feel cold or shivery, you are unwell or dehydrated, or the skin is weeping or painful, seek urgent medical advice through your GP or NHS 111, because widespread skin redness can affect temperature control and fluid balance, as the BAD notes.

The BAD says 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 widespread redness, and there are no specific blood tests to confirm PRP. The PCDS notes that patients tend to be referred to a specialist for both diagnosis and treatment.

The main alternative diagnosis is psoriasis, which the BAD says PRP is often mistaken for, particularly early on. Other causes of widespread redness, such as eczema and drug reactions, also have to be considered, which is the reason for the biopsy in uncertain cases. Distinguishing features include the orange tinge, the islands of sparing and the follicular plugs.

The BAD says that because of the rarity of PRP no studies including a large enough number of patients have been possible and there is no consensus on treatment. Topical and oral treatments, alone or in combination, are commonly used. For small areas, creams or ointments may be enough: steroid creams and ointments can improve the redness and scaling but probably do not alter the duration of the rash, and emollients are described as a very important part of treatment.

For extensive disease, the BAD says oral medicines should only be prescribed by a dermatologist after skin assessment and confirmation of the diagnosis. The most commonly used are acitretin and methotrexate, and phototherapy is also used in some cases, sometimes with acitretin. Biologic medicines, such as infliximab, ustekinumab, secukinumab and adalimumab, may be used especially when other treatments have not kept PRP under control. The PCDS agrees that no treatment is curative, that emollients are helpful, and that oral retinoids, most commonly acitretin, are usually highly effective.

These medicines carry important cautions and need monitoring, so they are prescribed and reviewed by a specialist team.

The natural history depends on the type. The BAD says the classic adult type has the best prognosis, with up to 80% clearing spontaneously within 3 years, and the PCDS says 60 to 80% resolve within 1 to 3 years with relapses uncommon. The atypical adult type may last 20 years or more according to the PCDS. The BAD stresses that individual circumstances differ.

Practical self-care includes liberal, regular use of emollients, which the BAD says help moisten dry skin and restore the barrier function of the skin. The BAD gives a fire-safety caution about emollients: when products get on dressings, clothing, bed linen or hair they can catch fire more easily, even once dry, so be careful near naked flames or lit cigarettes and wash clothing and bedlinen frequently. The BAD lists PRP Alliance and RareConnect as sources of peer support.

On the NHS the pathway usually runs from a GP to a dermatology clinic, where the diagnosis is confirmed and a treatment plan agreed, with oral and biologic medicines supervised by a specialist team. Private dermatology consultations are an alternative for faster assessment or a second opinion. Because PRP is rare and treatment is not guideline-based, it is reasonable to ask which treatments are proposed, what monitoring is needed and how long they should be tried before being reviewed.