Skin nontumor

Spongiotic, psoriasiform and pustular reaction patterns

Pityriasis rubra pilaris

Topic Completed: 1 August 2011

Minor changes: 9 November 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Pityriasis rubra pilaris [title] skin

Mowafak Hamodat, M.B.Ch.B., M.Sc.
Page views in 2020: 8,196
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Cite this page: Hamodat M. Pityriasis rubra pilaris. website. Accessed December 3rd, 2021.
Definition / general
  • Rare, chronic, papulosquamous dermatosis of unclear etiology
  • Salmon colored scaly patches, affecting elbows / knees or entire body, usually adults > age 40 years
Clinical features
  • Salmon colored scaly patches surrounding normal skin
  • Divided into five types: classic adult, atypical adult, classic juvenile, circumscribed or atypical juvenile
Case reports
  • Accutane
Clinical images

Images hosted on other servers:

Entire body affected except trunk

Various images

Microscopic (histologic) description
  • Biopsy from nonfollicular lesion consists of alternating orthokeratosis and parakeratosis in both vertical and horizontal directions
  • Focal or confluent hypergranulosis, thick suprapapillary plate, broad epidermal ridges, narrow dermal papillae and perivascular lymphocytic infiltrate in the superficial dermis
  • Small numbers of plasma cells and eosinophils may be present
  • Superficial blood vessels may appear slightly dilated
  • Occasionally, mild spongiosis with scattered intraepidermal lymphocytes
  • In early lesions, parakeratosis is poorly developed and lamellar ortho hyperkeratosis predominates; hypergranulosis is present and rete ridges are broadened and slightly elongated; the suprapapillary plate may be mildly thickened
Microscopic (histologic) images

Contributed by Hillary Rose Elwood, M.D.

PRP patient with alternating ortho and parakeratosis, focal follicular plugging

Differential diagnosis
  • Psoriasis: acanthosis is more marked and often strikingly regular, rete are thin and often fused, supapapillary plate is thinned, parakeratosis is usually confluent and characteristic collections of neutrophils are seen in overlying parakeratotic stratum corneum associated with spongiform degeneration of the underlying superficial epidermis
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