Skin nontumor

Spongiotic, psoriasiform and pustular reaction patterns

Pityriasis rubra pilaris



Last author update: 11 January 2024
Last staff update: 11 January 2024

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PubMed Search: Pityriasis rubra pilaris

Chau M. Bui, M.D.
Bruce R. Smoller, M.D.
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Cite this page: Bui CM, Smoller BR. Pityriasis rubra pilaris. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnontumorpityriasisrubra.html. Accessed April 14th, 2024.
Definition / general
  • Pityriasis rubra pilaris (PRP) is a rare, chronic, idiopathic disorder characterized by an acute cutaneous eruption with potential to quickly progress to erythroderma
Essential features
  • Includes acquired and hereditable forms
  • Clinical presentation is characterized by papulosquamous / erythematosquamous dermatosis
  • Affects all ages with variable clinical courses
  • Can be associated with HIV
  • CARD14 mutation has been detected in patients with familial PRP
  • Histopathologic findings are characteristic
ICD coding
  • ICD-10: L44.0 - pityriasis rubra pilaris
Epidemiology
Pathophysiology
Etiology
Clinical features
  • Can be localized or diffuse / erythroderma
  • Localized lesions are often found in elbows, knees and thighs
  • Characteristics are diffuse and confluent, orange-red, well defined plaques with normal appearing skin islands (sparing), scaling follicular papules and scaling on palms and soles
  • Variable degree of pruritus is common
  • Nail changes are common
  • Scalp alopecia or transient eruptive seborrheic keratosis with no evidence of an internal malignancy may occur (J Cutan Pathol 2021;48:133, Actas Dermosifiliogr 2014;105:955, Clin Exp Dermatol 2004;29:554, Acta Derm Venereol 1988;68:443, J Eur Acad Dermatol Venereol 2009;23:217, J Am Acad Dermatol 1989;20:801)
  • Cutaneous malignancies (e.g., basal cell carcinoma, Merkel cell carcinoma, squamous cell carcinoma and cutaneous Kaposi sarcoma) may also be present at the time of PRP diagnosis or ensuing months (Australas J Dermatol 2002;43:48, J Am Acad Dermatol 1996;35:781)
  • 6 types of PRP (Br J Dermatol 1996;135:1008)
    • Type I (classic adult type)
      • 55% of PRP patients
      • Presents with classic findings of PRP and spreads caudally
      • Majority clear within 3 years
    • Type II (atypical adult type)
      • 5% of PRP patients
      • Eczematous dermatitis with ichthyosiform scale on legs and palmoplantar keratoderma, occasional alopecia
      • Chronic clinical course
    • Type III (classic juvenile type)
      • 10% of PRP patients
      • Resembles type I
      • Erythroderma is less common
      • Majority clear within 3 years
    • Type IV (circumscribed juvenile type)
      • 25% of PRP patients
      • Circumscribed, erythematous follicular papules and scaly plaques on elbows and knees
      • Variable clinical course
    • Type V (atypical juvenile type)
      • 5% of PRP patients
      • Eczematous dermatitis with ichthyosiform scaly plaques, palmoplantar keratoderma, follicular hyperkeratosis and scleroderma-like changes of hands and feet
      • Onset in first few years of life
      • Chronic clinical course
    • Type VI
      • < 1% of PRP patients
      • Associated with HIV infection
      • Resembles type I
      • Follicular occlusion tetrad of dissecting cellulitis of the scalp, pilonidal sinus / cyst, hidradenitis suppurativa and acne conglobate may be accompanied
Diagnosis
  • Definitive diagnosis is based on clinicopathologic findings
    • Lesions most often appear on the face, chest and scalp with caudal migration interspersed with areas of unaffected skin
    • Small, scaly papules surround hair follicles
    • Palms or soles may develop an orange-red waxy keratoderma (Am J Clin Dermatol 2010;11:157)
  • Diagnosis is confirmed via biopsy in conjunction with clinical characteristics
    • Checkerboard pattern of parakeratosis and orthokeratosis is characteristic for PRP
    • Follicular plugging is common
    • Acantholysis and increased granular cell layer
    • No blood test is available; however, diagnosis of familial forms of PRP can be supported by Sanger sequencing for mutations of the CARD14 gene (Am J Clin Dermatol 2018;19:377)
Case reports
Treatment
Clinical images

Contributed by VisualDx
Erythroderma

Erythroderma

Perifollicular erythema and scale

Perifollicular erythema and scale

Orange palmoplantar keratoderma

Orange palmoplantar keratoderma

Ectropion and erythema

Ectropion and erythema

Microscopic (histologic) description
  • Orthohyperkeratosis alternating with parakeratosis in both horizontal and vertical directions (checkerboard pattern)
  • Follicular plugging
  • Mild, irregular, vaguely psoriasiform epidermal acanthosis with broad rete ridges, thick suprapapillary plates and preserved granular layer
  • Focal acantholysis, dyskeratosis may be seen (Am J Dermatopathol 1999;21:491)
  • Mild superficial perivascular and perifollicular lymphocytic infiltrate; rare eosinophils may be intermixed
  • Dilated vessels within papillary dermis
Microscopic (histologic) images

Contributed by Chau M. Bui, M.D.
Hyperkeratosis Hyperkeratosis

Hyperkeratosis and acanthosis

Checkerboard pattern Checkerboard pattern

Checkerboard pattern

Follicular plugging Follicular plugging

Follicular plugging

Sample pathology report
  • Skin biopsy, face:
    • Pityriasis rubra pilaris, classical adult type I (see comment)
    • Comment: The clinical history and images showing widespread erythema with areas of noninvolved skin present on the face, neck and trunk were reviewed. Histopathologic examination reveals hyperparakeratosis and orthokeratosis in a checkerboard pattern with hyperkeratotic plugging of a hair follicle. The clinical - pathologic findings are consistent with pityriasis rubra pilaris.
Differential diagnosis
  • Psoriasis (especially guttate):
    • Increased papillary dermal vascular ectasia
    • More parakeratosis
    • More likely to have hypogranulosis and intracorneal neutrophils
  • Digitate dermatosis (small plaque parapsoriasis):
    • More lymphocyte exocytosis
    • Less prominent orthoparakeratotic hyperkeratosis
  • Sézary syndrome:
  • Phrynoderma (vitamin A deficiency):
    • Less psoriasiform epidermal hyperplasia
  • CARD14 associated papulosquamous eruption:
Board review style question #1

What is the most specific histologic finding of pityriasis rubra pilaris (PRP)?

  1. Checkerboard hyperkeratosis pattern
  2. Hyperkeratosis and perivascular lymphocytic infiltrate
  3. Psoriasiform epidermal hyperplasia
  4. Sparse superficial inflammation
Board review style answer #1
A. Checkerboard hyperkeratosis pattern. Alternating vertical and horizontal orthoparakeratosis and parakeratosis (checkerboard pattern) is characteristic for PRP. Answer B is incorrect because perivascular lymphocytic infiltrate with hyperkeratosis is more commonly seen in cases of psoriasis. Answer D is incorrect because sparse superficial inflammation is more characteristic of eczema. Answer C is incorrect because psoriasiform patterns can be found in a wide variety of skin disorders and is not specific for PRP.

Comment Here

Reference: Pityriasis rubra pilaris
Board review style question #2
What is the mutation associated with pityriasis rubra pilaris (PRP)?

  1. BRAF
  2. CARD14
  3. KRAS
  4. TERT
Board review style answer #2
B. CARD14. Mutations in CARD14 have been identified in the familial form of PRP. Answers A and D are incorrect because these mutations are found more commonly in melanomas but not identified in PRP. Answer C is incorrect because KRAS mutations are found in a wide variety of cancers but have not been identified in PRP to date.

Comment Here

Reference: Pityriasis rubra pilaris
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