Pityriasis rubra pilaris
Pityriasis rubra pilaris (PRP) is characterized by an acute cutaneous eruption that is often accompanied by pruritus and/or pain. There are both acquired and heritable forms. Classic cutaneous lesions include follicular papules on an erythematous base coalescing to form large, orange-red plaques with characteristic islands of sparing. PRP commonly begins on the scalp and rapidly spreads in a craniocaudal direction and has the potential to quickly progress to erythroderma over several weeks' time. Additional features include an orange-red palmoplantar keratoderma. PRP can be classified into 6 clinical types:
- Type I (classic adult type, 55% of cases) – Occurs in adults. It is the most common subtype and is associated with a good prognosis, with the majority of cases clearing within 3 years. Relapses are uncommon.
- Type II (atypical adult type, 5% of cases) – A rare subtype seen in adults. It is characterized by a chronic course with most cases lasting longer than 3 years.
- Type III (classic juvenile type, 10% of cases) – Occurs in children younger than 2 years old and adolescents. It resembles type I PRP clinically and is associated with a benign disease course. Most cases resolve in 3 years, but some cases persist longer.
- Type IV (circumscribed juvenile type, 25% of cases) – Most common subtype in children and adolescents. It is characterized by focal lesions on extremities and a prepubescent onset. Clinical course is variable.
- Type V (atypical juvenile type, 5% of cases) – Typically occurs in the first few years of life or at birth. It is the most common familial form of PRP. It may resemble type II PRP clinically and may follow a chronic course.
- Type VI (HIV-associated type, < 1% of cases) – Occurs in HIV-infected individuals. It may resemble type I PRP, but additional features are common. It is typically resistant to treatment.
- Facial discoid dermatitis has been proposed as type VII PRP. It presents on the face and has histologic features of PRP. It is typically resistant to topical therapy.
While there are reports of heritable forms, the large majority of PRP cases are acquired and without sex predilection. The incidence of the acquired form occurs in 2 peaks: during the first and second decades and during the sixth decade.
For more information, see OMIM.
L44.0 – Pityriasis rubra pilaris
3755001 – Pityriasis rubra pilaris
- Psoriasis – See Diagnostic Pearls.
- Seborrheic dermatitis – Much more responsive to standard therapies. PRP is often resistant to conventional therapies for seborrheic dermatitis. In addition, the progression of body surface involvement will distinguish PRP from seborrheic dermatitis.
- Mycosis fungoides / Sézary syndrome – Generalized lymphadenopathy, circulating malignant lymphocytes as determined by flow cytometry, leonine facies, and a CD4 / CD8 ratio greater than 10 as determined by flow cytometry.
- Erythrokeratodermia variabilis – More than 90% of patients present within the first year of life.
- Drug eruption – Often presents with urticarial, exanthematous, or vesicular / bullous lesions. In addition, systemic symptoms are more pronounced, including fever, lymphadenopathy, and facial edema. Eosinophilia on CBC and histology are often seen (but not an invariable finding). Medication history will help.
- Atopic dermatitis – Patients are often aware of their atopic history, and the condition commonly starts in childhood. Look for lichenified plaques on the flexural surfaces and neck.
- Caspase recruitment domain family member 14 gene (CARD14)-associated papulosquamous eruption refers to a distinctive phenotype with overlapping features of psoriasis and PRP. The patients typically present early in life and report a family history of psoriasis or PRP. The cheeks, chin, and ears are typically affected. This disease is difficult to treat using conventional therapies, while treatment with ustekinumab appears to be effective.