Pityriasis Rubra Pilaris Workup

Updated: Sep 11, 2020
  • Author: Philip D Shenefelt, MD, MS; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

No specific laboratory tests are available to confirm the diagnosis of pityriasis rubra pilaris (PRP). The diagnosis is usually made on the basis of a correlation between clinical findings and histologic findings. [19]

Perform tests for electrolyte abnormalities, hypoalbuminemia, secondary bacterial infection in the skin, and possible sepsis.

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Procedures

Perform a biopsy.

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Histologic Findings

Histologic features are not pathognomonic, but they are useful to rule out other possible papulosquamous and erythrodermic disorders. Features on light microscopy include hyperkeratosis with alternating orthokeratosis and parakeratosis forming a checkerboard pattern in the stratum corneum, focal or confluent hypergranulosis, follicular plugging with perifollicular parakeratosis forming a shoulder effect, thick suprapapillary plates, broad rete ridges, narrow dermal papillae, and sparse superficial dermal lymphocytic perivascular infiltration. Acantholysis has been reported as an additional histologic finding in pityriasis rubra pilaris. [9] Acantholysis may be restricted to adnexal epithelium. The presence of acantholysis, hypergranulosis, follicular plugging, and the absence of dilated capillaries and epidermal pustulation may help distinguish pityriasis rubra pilaris from psoriasis. [20, 21]

Features on electron microscopy include a decreased number of keratin filaments and desmosomes, enlarged intercellular spaces, parakeratosis with lipidlike vacuoles, large numbers of lamellar granules, and a focal split in the basal lamina at the dermoepidermal junction.

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