Which histologic findings are characteristic of Riehl melanosis (pigmented contact dermatitis)?

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