High ratio of IgG4-positive plasma cell infiltration in cutaneous plasmacytosis--is this a cutaneous manifestation of IgG4-related disease?

Cutaneous plasmacytosis is a rare condition affecting middle-aged individuals, characterized by multiple red-brown papules and plaques over the trunk. It has been reported mainly in Japan. The condition is accompanied by polyclonal hypergammaglobulinemia and superficial lymphadenopathy. Lung or retroperitoneal involvement occurs rarely. In the present study, 3 consecutive cases of cutaneous plasmacytosis were observed histologically to have abundant infiltration of IgG4-bearing plasma cells. All 3 were associated with superficial lymphadenopathy, one with interstitial lung involvement showing ground-glass opacity on computed tomography and the others with bone marrow plasmacytosis, showing histologic evidence of more IgG4-positive plasma cells. All 3 had polyclonal hypergammaglobulinemia, one had high serum concentration of IgG4, and all had elevated serum IL-6. The ratios of IgG4+ to IgG+ plasma cells were assessed using skin biopsy specimens with pemphigus (n = 7), discoid lupus erythematosus (n = 5), and morphea (n = 2) (mean ratios, 19%, 0%, and 0%, respectively); we noted the proportion of IgG4-positive plasma cells in cutaneous plasmacytosis (mean, 48%). IgG4-related sclerosing disease is a newly recognized systemic disorder characterized by lymphoplasmacytic infiltration and fibrosis and by a high serum IgG4 level and increased IgG4-positive plasma cells in the tissues. Skin manifestations of this disorder have not been described. Although cutaneous plasmacytosis could be a chronic allergic hypersensitivity reaction, our findings raise the possibility of a relationship in pathogenesis between cutaneous plasmacytosis and IgG4-related sclerosing disease.