Prurigo Nodularis Workup

Updated: Nov 13, 2020
  • Author: Amarateedha Prak LeCourt, MD; Chief Editor: William D James, MD  more...
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Workup

Laboratory Studies

Perform a CBC count and a chemistry panel, including liver function tests (LFTs), to help exclude underlying hematologic malignancies, renal failure, and hepatic diseases.

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Procedures

Obtaining skin biopsy samples of prurigo nodularis skin lesions for histologic examination and/or cultures may be indicated to exclude squamous cell carcinoma (particularly the keratoacanthoma type) and infections (especially deep fungal, atypical mycobacterial).

Patch testing to exclude contact sensitivity may be considered, particularly with coexisting dermatitis.

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Histologic Findings

The histologic features of prurigo nodularis [22] include a hyperkeratotic epidermis with acanthosis and parakeratosis. Rete ridges are elongated and irregular with a dense dermal infiltrate consisting of neutrophils, eosinophils, histiocytes, and monocytes. [23] Also notable in the dermis are thickened nerve fibers and fibrosis with thickened collagen bundles. Thickened nerve fibers are dilated on electron microscopy. Schwann cells show vacuolization and degeneration with no detectable mitochondria. Axons and Schwann cells both show hyperproliferation. [22, 24]

Highly characteristic for prurigo nodularis is the presence of thick, compact orthohyperkeratosis; irregular epidermal hyperplasia or pseudoepitheliomatous hyperplasia; focal parakeratosis or superficial epithelial necrosis; hypergranulosis; fibrosis of the papillary dermis with vertically arranged collagen fibers; increased number of fibroblasts and capillaries; a superficial, perivascular and/or interstitial inflammatory infiltrate of lymphocytes, macrophages and, to a lesser extent, eosinophils and neutrophils. Correlation of clinical and histological findings is necessary to reliably distinguish between prurigo nodularis and lichen simplex chronicus, [25] although both disorders may coexist in the same patient and both are a reaction to rubbing or scratching the skin.

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