Pityriasis Rubra Pilaris (PRP)

• Disorder of keratinization with bimodal distribution involving children and adults, nearly always acquired (occasional familial cases described)
• Presents with
  • Hyperkeratotic follicular papules on erythematous base, which coalesce into large orange-red to red patches with characteristic ‘ islands of sparing’
  • Palms and soles with waxy orange-red keratoderma
  • May rapidly evolve into erythroderma
  • Nail changes include subungual hyperkeratosis and nail plate thickening
• 5 types:
  • Type I and II in adults, Type III–V in children (see Chap. 2 for pediatric types)
    • Type I (classic): over half of all cases; sudden onset of symptoms with duration of 2–5 years
    • Type II (atypical): about 5% cases, slow onset with alopecia, localized lesions and chronic course
• Histology: acanthosis, thickened granular layer, ‘checkerboard parakeratosis’ (orthokeratosis alternating with parakeratosis both vertically and horizontally), ‘shoulder parakeratosis’ adjacent to follicular plugs, perivascular lymphocytic infiltrate
• Treatment: high potency topical corticosteroid, systemic retinoid, methotrexate, ± phototherapy, azathioprine, infliximab