Pityriasis rubra pilaris

Pityriasis rubra pilaris (PRP) is the name given to a group of rare skin conditions characterised by orange-red erythema, scaly lesions, and palmoplantar keratoderma. It may be generalised of localised. PRP may progress to erythroderma with distinct areas of uninvolved skin, the so-called islands of sparing.

This chapter is set out as follows:

• The aetiology is unknown
• Although most cases are sporadic, a familial form exists with an autosomal dominant inheritance pattern

• Males and females are equally affected 
• Pruritus may be present in the early stages 

Five types of PRP have been described:

Type I: Adult-onset classical

• ​The most common type, accounting for 50% of all cases, presenting most commonly between the ages of 40-60 years. Males and females are affected equally
• There may be an insidious onset with erythematous macules
• Follicular papules then develop and start to coalesce to form sheets of erythema, that have an orange tinge
• The rash spreads from the head to the feet, with bran-like scaling of scalp
• There is uniform erythema of the face, but on the trunk and limbs there is sharply demarcated islands of unaffected skin
• The palms and soles become hyperkeratotic and orange-yellow, and the nails thickened. Rough, scaly papules (follicular hyperkeratosis) are commonly seen on the dorsal aspects of the proximal phalanges, the elbows, and the wrists 
• Patients with extensive disease may develop ectropion
• Erythroderma develops within 2-3 months with widespread erythema and constitutional symptoms 
• 60-80% have resolution within 1-3 years, and relapses are uncommon

Type II: Adult-onset atypical

• ​Is characterised by ichthyosiform lesions, areas of eczematous change, alopecia, and long duration (often 20 years or more) 

Type III: Juvenile-onset classical

• Usually presents between the ages of 5-18 years
• It may develop rapidly after an acute infection
• The clinical pattern is very similar to type I
• There tends to be spontaneous clearance around one year

Type IV: Juvenile-onset circumscribed

• ​Is the second most common type of PRP, and usually presents under the age of 12 years
• It presents with well-demarcated plaques of follicular plugging on the elbows and knees, and sometimes the palms and soles
• The natural history is not well described, although it may improve in the late teens 

Type V: Juvenile-onset atypical

• ​This is sometimes inherited
• There is erythema and hyperkeratosis from a young age, along with significant ichthyosis
• It is generally very persistent

• Patients tend to be referred to a specialist for both diagnosis and treatment

• Although no treatment is curative, emollients are helpful, and oral retinoids (most commonly acitretin) are usually a highly effective treatment