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Spongiotic, psoriasiform and pustular reaction patterns

Pityriasis rubra pilaris

Authors: Chau M. Bui, M.D., Bruce R. Smoller, M.D.

Editorial Board Member: Bethany R. Rohr, M.D.

Last author update: 11 January 2024

Last staff update: 11 January 2024

Copyright: 2002-2025, PathologyOutlines.com, Inc.

PubMed Search: Pityriasis rubra pilaris

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Table of Contents

Cite this page: Bui CM, Smoller BR. Pityriasis rubra pilaris. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnontumorpityriasisrubra.html. Accessed January 22nd, 2025.

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

All ages, 2 peaks: first and sixth to seventh decades (JAMA Dermatol 2016;152:670)
No gender difference (JAMA Dermatol 2016;152:670)
Large majority of PRP cases are acquired (Am J Clin Dermatol 2018;19:377)
HIV associated type VI PRP (Br J Dermatol 1996;135:1008)

Sites

Skin, nails and hair (Pediatr Dermatol 1986;3:446, Arch Dermatol 1964;89:515)

Pathophysiology

CARD14 mutation and dysfunction of vitamin A metabolism have been suggested to play a role in the pathogenesis (Br J Dermatol 1981;104:253, J Cutan Pathol 2020;47:425)

Etiology

Etiology not clearly defined (Am J Clin Dermatol 2018;19:377)
Onset of acquired PRP has been associated with malignancy, infection, medications, vaccines, ultraviolet exposure and skin trauma (Am J Clin Dermatol 2010;11:157)
Heritable PRP is associated with CARD14 mutation (Am J Hum Genet 2012;91:163)

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

49 year old man with paraneoplastic PRP preceding leukemia (Adv Skin Wound Care 2022;35:1)
60 year old woman with acantholytic PRP induced by topical use of imiquimod 5% (An Bras Dermatol 2020;95:63)
65 year old man with PRP following COVID-19 vaccine (JAAD Case Rep 2022;24:74)
68 year old man with PRP with involvement of tongue and palate (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:604)
70 year old woman with identification of a pathogenic CARD14 mutation in PRP (BMJ Case Rep 2021;14:e235287)
72 year old woman with paraneoplastic PRP (JAAD Case Rep 2023;39:125)

Treatment

Topical corticosteroids, topical or oral retinoids, cyclosporine, methotrexate, vitamin D analogs, antitumor necrosis factors (anti-IL12 / IL23 or anti-IL17 biologics, either alone or in combination therapy), azathioprine, intravenous immunoglobulin, infliximab, ixekizumab, tildrakizumab, ustekinumab, secukinumab, adalimumab, upadacitinib, narrowband UVB and extracorporeal photochemotherapy (Am J Clin Dermatol 2010;11:157, Am J Clin Dermatol 2018;19:377, Arch Dermatol 2005;141:423, J Am Acad Dermatol 2018;79:353, JAAD Case Rep 2022;27:55, JAAD Case Rep 2023;35:112, Australas J Dermatol 2022;63:120, Clin Exp Dermatol 2022;47:2300, Int J Rheum Dis 2023;26:1157, Dermatol Ther 2020;33:e14097, Clin Exp Dermatol 2021;46:1594, SAGE Open Med Case Rep 2023;11:2050313X231160927)

Clinical images

Contributed by VisualDx

Erythroderma

Perifollicular erythema and scale

Orange palmoplantar keratoderma

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 and acanthosis

Checkerboard pattern

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:
- Atypical lymphocytes (large, hyperchromatic or convoluted nuclei) in a sparse dermal infiltrate (Semin Cutan Med Surg 2018;37:18)
Phrynoderma (vitamin A deficiency):
- Less psoriasiform epidermal hyperplasia
CARD14 associated papulosquamous eruption:
- Regular psoriasiform acanthosis with elongated rete ridges
- Lacks acantholysis (J Cutan Pathol 2020;47:425)

Board review style question #1

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

Checkerboard hyperkeratosis pattern
Hyperkeratosis and perivascular lymphocytic infiltrate
Psoriasiform epidermal hyperplasia
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.

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Reference: Pityriasis rubra pilaris

Board review style question #2

What is the mutation associated with pityriasis rubra pilaris (PRP)?

BRAF
CARD14
KRAS
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.

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Reference: Pityriasis rubra pilaris

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