Pityriasis Rubra Pilaris

Pityriasis rubra pilaris is a rare long-term inflammatory skin condition. The name means scaling (pityriasis), redness (rubra), and involvement of the hair follicles (pilaris). It affects all races and sexes equally. 

It is classified into six clinical types:

• Type I is the most common and is called ‘classic adult type.’ 
• Type II is a variation of type I, known as the atypical adult-onset. 
• Type III, IV, and V represent classically, circumscribed, and atypical juvenile forms.
• Type VI is associated with HIV-associated PRP (human immunodeficiency virus infection). 

The cause of pityriasis rubra pilaris is not known. It is not an infection and, therefore, cannot be passed on to others.

Pityriasis rubra pilaris is usually not hereditary, but there are family cases described associated with a genetic predisposition. 

• A rash that can be itchy in its early stages. 
• The thick skin on the palms and soles splits and becomes painful. Walking may be difficult.
• Shivering, heat and fluid loss may occur if the rash covers large areas of skin.

The main features of the most common – Type I (classic adult) of pityriasis rubra pilaris are as follows: 

• The rash usually starts suddenly on the scalp and spreads to cover much of the chest and abdomen.
• The patches are dry, scaly, and red with an orange tinge and have well-defined edges. Smaller patches may join together to cover large areas of skin. Occasionally, people with pityriasis rubra pilaris can become red all over; this is called erythroderma. 
• Areas of normal-looking skin, where there is no rash, known as ‘spared areas,’ can often be seen lying between larger red patches. 
• The hair follicles in the affected areas can feel rough to the touch because of the build-up of scale at their base (follicle plugs).
• The skin on the palms and soles may become thickened and have an orange color. The nails may thicken and be discolored and sometimes shed. 

The Type II (atypical adult) accounts for 5% of all PRP cases and does not follow the head to toe progression described above. It typically affects the legs with thickening of the skin on the palms and soles. It can also be associated with hair loss on the body.

Type III accounts for 10% of all cases. Presentation is similar to Type I but starts in childhood. 

Type IV (circumscribed juvenile) accounts for 25% of cases. It affects children before puberty and is characterized by well-defined red patches, hair follicle plugs on the knees and elbows, and thickening of the skin on the palms and soles. 

Type V represents 5% of cases. It is commonly familial, i.e., there are other family members affected. It starts early in life with dryness, hair follicle plugs, and sometimes thickened skin on the hands and feet.

Type VI is seen in people with HIV and is characterized by red, scaly spots around the hair follicles and may or may not involve the palms and soles. 

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. Skin biopsy is where a small piece of skin is removed under a local anesthetic and examined under a microscope. A referral to a skin specialist may be made by the doctor to confirm a diagnosis. 

There are no specific blood tests to confirm pityriasis rubra pilaris. The different types of pityriasis rubra pilaris may look like psoriasis and are often mistaken for psoriasis, especially at the early stages.

The natural history of pityriasis rubra pilaris depends on the type. Due to its rarity, no large size studies, including patients, have been possible, and there is no consensus on treatment. Multiple topical and systemic treatments can be used, and there is a tendency, in the majority of cases, towards a sudden natural resolution. The ‘classic adult type’ has the best prognosis, with up to 80% spontaneously resolving within three years.

There are no treatment guidelines for PRP. Topical and systemic treatments, alone or in combination, are commonly used. 

Creams or ointments applied to the skin may be all that is required if the pityriasis rubra pilaris is affecting small areas of the body:

• Steroid creams and ointments.
• Emollients (moisturizers).

Tablet medications may be needed if the pityriasis rubra pilaris is very extensive. A dermatologist should only prescribe these medications after skin assessment and confirmation of the diagnosis. The most commonly used are acitretin and methotrexate tablets. Phototherapy (light therapy) is also used in some cases.

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 specific protein involved in causing PRP. These include infliximab, ustekinumab, secukinumab, and adalimumab.