The cause of pityriasis rubra pilaris is unknown.
The 2 most common forms of the disorder are
Atypical (nonclassic) forms exist in both age groups. Sunlight, HIV or another infection, minor trauma, or an autoimmune disorder may trigger a flare-up.
Diagnosis of pityriasis rubra pilaris is by clinical appearance and may be supported by biopsy.
Biopsy is done when the clinical diagnosis is unclear (eg, when the patient is erythrodermic at presentation).
Differential diagnosis of pityriasis rubra pilaris includes the following:
Treatment of pityriasis rubra pilaris is exceedingly difficult and empiric. The disorder may be ameliorated but almost never cured; classic forms of the disorder resolve slowly over 3 years, whereas nonclassic forms persist. Scaling may be reduced with emollients or 12% lactic acid under occlusive dressing, followed by topical corticosteroids. Oral vitamin A may be effective. Oral acitretin (a retinoid) or methotrexate is an option when a patient is resistant to topical treatment.
Phototherapy, immunomodulatory agents (biologics), cyclosporine, mycophenolate mofetil, azathioprine, and corticosteroids have also been used (1).
1. Eastham AB, Femia A, Qureshi A, et al: Treatment options for pityriasis rubra pilaris including biologic agents: A retrospective analysis from an academic medical center. JAMA Dermatol 150(1):92–94, 2014. doi:10.1001/jamadermatol.2013.4773.