Pityriasis Rubra Pilaris — SCE Dermatology MCQ

Correct answer: D — Acitretin

The correct answer is D, Acitretin. This man has classic (type I) pityriasis rubra pilaris, identified by follicular keratotic papules coalescing into orange-red plaques with nappes claires and waxy orange palmoplantar keratoderma. Oral retinoids are considered first-line systemic therapy for PRP, acting via normalisation of keratinocyte differentiation and reduction of hyperproliferation, typically dosed around 0.5 to 0.75 mg/kg/day and continued for months given the slow natural resolution of classic disease. Acitretin has the largest evidence base and longest track record among systemic options for PRP and is the standard first choice before escalating to second-line agents such as methotrexate or biologics in refractory cases. Why the other options are wrong: C. Ciclosporin: reserved for rapid disease control in severe or erythrodermic PRP unresponsive to retinoids, not first-line due to nephrotoxicity and hypertension risk with long-term use. A. Methotrexate: used as a second-line agent, either alone or combined with retinoids, when acitretin fails or is contraindicated, but lacks the primary evidence base acitretin has. E. Prednisolone: systemic steroids give only short-term symptomatic relief and do not address the underlying keratinisation defect, with risk of rebound flare on withdrawal. B. Dapsone: not established therapy for PRP, its mechanism (anti-neutrophilic, used in dermatitis herpetiformis and neutrophilic dermatoses) is irrelevant to the keratinocyte pathology of PRP. Key point: In classic adult PRP with orange keratoderma and nappes claires, oral acitretin is the first-line systemic treatment, with methotrexate and biologics reserved for refractory disease.

Reference: DermNet NZ, Pityriasis Rubra Pilaris, Treatment section (systemic retinoids, particularly acitretin, as first-line therapy), https://dermnetnz.org/topics/pityriasis-rubra-pilaris