Chapter 168. Pigmented Purpuric Dermatoses

The pigmented purpuric eruptions are a group of dermatoses characterized by petechiae, pigmentation, and, occasionally, telangiectasia in the absence of associated venous insufficiency or hematologic disorders (Table 168-1). Synonyms include persistent pigmented purpuric dermatitis, purpura simplex, and purpura pigmentosa chronica. They are found most commonly on the lower extremities; however, the lesions may involve the upper body and rarely become generalized. There are reports of palm, sole, genital, and oral mucosal involvement. These benign, generally asymptomatic eruptions tend to be chronic, with remissions and flares. They share common histopathology features, including capillaritis, erythrocyte extravasation, and hemosiderin deposition.

Pigmented purpuric eruptions are rare. There seems to be no ethnic or gender predisposition, and most patients are in their 30s and 40s (see Table 168-1), but children may be affected.

There are three different views of the pathogenesis of pigmented purpuric eruptions. The first is that they are due to a disturbance or weakness of the cutaneous blood vessels, leading to capillary fragility and erythrocyte extravasation. However, this does not account for the inflammatory infiltrate common to these disorders. The second proposed mechanism is humoral immunity. This suggested pathogenesis is supported by direct immunofluorescent studies showing vascular deposition of C3, C1q, immunoglobulin M, or immunoglobulin A. However, several cases have not shown these deposits. The third proposed mechanism is cellular immunity.1,2 The infiltrate in pigmented purpuric dermatoses consists of lymphocytes, macrophages, and Langerhans cells. This inflammatory infiltrate leads to vascular fragility and subsequent leakage of erythrocytes. Aiba and Tagami used immunohistologic studies in eight cases of Schamberg disease to demonstrate that the dermal infiltrate was predominantly composed of helper–inducer T cells and OKT6-reactive cells,3 whereas the epidermis showed intercellular staining with human leukocyte antigen (HLA)-DR antibody and OKT6 antibody. Based on this study, they concluded that a cellular immune reaction, specifically the Langerhans cell, likely plays an important role in the pathogenesis.