Pityriasis rubra pilaris

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Pityriasis rubra pilaris
Diagnosis in short

LM alterating orthokeratosis and parakeratosis (known as "checkerboard pattern"), marked uniform acanthosis with broad dermal papillae and broad epidermal ridges, , +/-eosinophils (common), follicular plugging, scattered foci of acantholysis (common), occasional mild spongiosis
LM DDx fungal infection, psoriasis, Darier disease, seborrhoeic dermatitis
Stains PASD -ve (to r/o fungal infections)
IF negative (changes in Desmoglein 1 & Desmoglein 3 in pemphigus vulgaris)
Gross salmon-coloured plaques, well-demarcated
Site skin - see inflammatory skin disorders

Associated Dx HIV infection - recalcitrant PRP
Clinical history Classic adult - self-limited exfoliative, erythematous dermatitis that starts over the head and neck and extends downwards forming orange plaques with spared islands of normal skin, follicular hyperkeratosis, palmar involvement with orange hyperkeratosis
Prevalence uncommon
Treatment retinoids, methotrexate and others

Pityriasis rubra pilaris, abbreviated PRP, is an uncommon inflammatory skin disorder.


  • Uncommon.[1]
  • Typically sporadic, may be familial.[2]
  • Bimodal age distribution:[3]
    • Children: <10 years.
    • Adults: 40s and 50s.


  • Retinoids, methotrexate and others.[3]


  • Salmon-coloured (red) plaques interrupted by well-demarcated normal appearing skin.[3]



  • Alterating orthokeratosis and parakeratosis - known as "checkerboard pattern".
  • Marked uniform acanthosis with broad dermal papillae and broad epidermal ridges.
  • Follicular plugging.
  • +/-Eosinophils (common).
  • Scattered foci of acantholysis.[4]
  • Occasional mild spongiosis.


  • PRP is easy to miss - clinical history (r/o PRP) usually needed to prompt correct diagnosis.

Microscopic DDx

  • Psoriasis vulgaris[5] - thinned suprapapillary plates, hypogranulosis, neutrophils in the stratum corneum, dilated papillary dermal blood vessels, acantholysis absent.
  • Lichen simplex chronicus - usually a localized process, not a widespread process.
  • Darier disease - acantholysis is prominent with corps ronds and grains, follicular plugging absent.
  • Pemphigus vulgaris - PRP with extensive acantholysis can mimic; IF will be negative in PRP.
  • Hailey-Hailey disease - falling brick wall pattern of acantholysis.
  • Seborrhoeic dermatitis - more spongiotic, often with neutrophils.
  • Fungal infection.

Associated Diagnoses



See also


  1. 1.0 1.1 Marrouche, N.; Kurban, M.; Kibbi, AG.; Abbas, O. (Apr 2014). "Pityriasis rubra pilaris: clinicopathological study of 32 cases from Lebanon.". Int J Dermatol 53 (4): 434-9. PMID 24783259.
  2. Mercer, JM.; Pushpanthan, C.; Anandakrishnan, C.; Landells, ID.. "Familial pityriasis rubra pilaris: case report and review.". J Cutan Med Surg 17 (4): 226-32. PMID 23815954.
  3. 3.0 3.1 3.2 Klein, A.; Landthaler, M.; Karrer, S. (2010). "Pityriasis rubra pilaris: a review of diagnosis and treatment.". Am J Clin Dermatol 11 (3): 157-70. doi:10.2165/11530070-000000000-00000. PMID 20184391.
  4. 4.0 4.1 4.2 Leger, M.; Newlove, T.; Robinson, M.; Patel, R.; Meehan, S.; Ramachandran, S. (Dec 2012). "Pityriasis rubra pilaris.". Dermatol Online J 18 (12): 14. PMID 23286804.
  5. Brinster, NK. (Mar 2008). "Dermatopathology for the surgical pathologist: a pattern based approach to the diagnosis of inflammatory skin disorders (part I).". Adv Anat Pathol 15 (2): 76-96. doi:10.1097/PAP.0b013e3181664e8d. PMID 18418089.