What are the histologic findings of pigmented purpuric dermatoses?

Updated: Aug 12, 2019
  • Author: Darius Mehregan, MD; Chief Editor: Dirk M Elston, MD  more...
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Answer

Histologically, a perivascular infiltrate of lymphocytes and macrophages is centered on the superficial small blood vessels of the skin. Signs of endothelial cell swelling and narrowing of lumina may be seen, as demonstrated in the image below.

Endothelial cell swelling is a histologic feature Endothelial cell swelling is a histologic feature of capillaritis. This biopsy sample was obtained from a patient with lichen aureus.

The infiltrate is composed of predominantly CD4+ lymphocytes along with occasional CD1a+ dendritic cells. Plasma cells and neutrophils are occasionally present; the latter is not uncommon in lesions of itching purpura. Extravasation of red blood cells with marked hemosiderin deposition in macrophages is typically seen, as demonstrated in the image below. However, the degree of hemosiderin deposition may be variable, and it can be minimal in early lesions of itching purpura. [19]

Hemosiderin deposition is seen in dermal macrophag Hemosiderin deposition is seen in dermal macrophages in this biopsy sample obtained from a patient with lichen aureus.

Histochemical staining with Perls stain and Fontana-Masson stain, to demonstrate iron (hemosiderin) and exclude melanin pigment respectively, may be helpful. Hemosiderin deposition in the dermis is more superficial in pigmented purpuric dermatitis than that seen in stasis dermatitis, which is a useful differentiating feature. Mild epidermal spongiosis and exocytosis of lymphocytes may be seen in all variants except lichen aureus, which, in general, tends to show a bandlike infiltrate separated from the epidermis by a thin rim of uninvolved collagen.

Kerns et al described an unusual variant of pigmented purpuric dermatoses, granulomatous pigmented purpura, in a 42-year-old white woman, and Wong et al reported 2 cases of a similar variant. [20, 21]


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