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
Treatment of Pityriasis Rubra Pilaris
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 Treatment reference Pityriasis rubra pilaris is a rare chronic disorder that causes hyperkeratotic yellowing of the skin, including the trunk, extremities, and, particularly, the palms and soles. Red follicular... read more 
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Treatment reference
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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
