IgG4-related Sclerosing disease: a potential new etiology of cutaneous pseudolymphoma.

IgG4-related sclerosing disease is a syndrome characterized by the involvement of a wide variety of tissues by lymphoplasmacytic infiltrates and sclerosis, elevated serum IgG4 titer, and increased IgG4+ plasma cells in tissues. This report describes 2 cases with skin involvement, a feature not well documented in the literature. The patients had plaques or nodules in the skin of the cheek, temporal or periauricular region. Histologically, there was dermal and subcutaneous involvement by a nodular lymphoid infiltration often interspersed with lymphoid follicles and sclerotic stroma. The infiltrate was rich in plasma cells, small lymphocytes, and sometimes plasmablasts. The IgG4+ cell count was high (342 to 425 per high power field), with an IgG4/IgG proportion from 68% to 100%. As the morphology was compatible with pseudolymphoma, 14 cases of cutaneous pseudolymphoma were retrieved from the archives for IgG4 and IgG immunostaining. Two cases exhibited marked increase in IgG4+ cells, and showed many similarities with cutaneous manifestation of IgG4-related sclerosing disease, but the limited available clinical information precluded a conclusion on their nosologic nature. In summary, IgG4-related sclerosing disease can manifest with skin lesions, and is also one of the potential etiologies of cutaneous pseudolymphomas.