Riehl Melanosis (Pigmented Contact Dermatitis) Workup

Updated: May 27, 2021
  • Author: Elizabeth K Satter, MD, MPH; Chief Editor: William D James, MD  more...
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Workup

Procedures

Perform closed patch testing with the standard series, cosmetic series, fragrance series, and patient's personal products.

Photo-patch testing may also be warranted.

Provocative use test or repeated open application test (ROAT) is performed when closed patch testing results are equivocal or negative. The concentration of the allergen (eg, preservatives, fragrances) may be too low in the cosmetic series to produce a positive reaction on the back. [7]

Skin biopsy typically is not required unless there is an unusual clinical presentation.

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Histologic Findings

Biopsies from lesional skin show both an increase in the number and the activation of melanocytes in the basal layer, in addition to typical interface changes associated with dermal pigment incontinence, a superficial lymphocytic infiltrate, and vascular proliferation. However, unlike other acquired disorders of macular pigmentation, a significant percentage of normal perilesional skin from patients with Riehl melanosis also show similar perivascular inflammation, focal vacuolar degeneration (but to somewhat of a lesser degree than lesional skin), and increased numbers of dermal fibroblasts containing melanosome particles. Findings suggestive of spongiosis are lacking. [40] Some biopsy specimens have shown mild atrophy of the dermis, but this is an inconsistent finding. Negative direct immunofluorescence study results help eliminate hyperpigmented lupus erythematosus from the differential diagnosis.

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Other Tests

Dermoscopy

The most distinctive dermatoscopic features are a pseudonetwork consisting of prominent nonpigmented follicular openings associated with peripheral pigmentation admixed with gray dots/granules, which corresponds to pigment incontinence (melanophages located in papillary dermis). Additional dermatoscopic features include a perifollicular whitish halo, follicular keratotic plugs, and telangiectasias. Lastly, flourlike slight scale has also been reported, and this feature seems to be unique to Riehl melanosis because it is not seen in other acquired macular hyperpigmentation disorders. [41, 42, 43] A 2019 study reviewed the dermatoscopic features on the face, as compared to the neck, and found that although these regions show similar dermatoscopic findings, there were subtle differences. [44] For example, on the cheek, a hypopigmented network pattern was not observed, whereas on the neck, follicular keratotic plugs and a perifollicular halo were less common. [44]

Microscopy

The most distinctive feature on reflectance confocal microscopy is the presence of pigment incontinence consisting of melanophages primarily concentrated in the superficial dermal papilla, associated with a few scattered round-to-polygonal, mildly refractive cells. [45] Additional features include total or partial obliteration of the ringlike structures around the dermal papillae, consistent with the presence of liquefaction of the basal cells, a variable degree of dilated infundibulum, and hyperkeratotic adnexal infundibula. [45]

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