IgG4-Related Cutaneous Vasculitis Presenting as Multiple Subcutaneous Nodules.

A 66-year-old woman presented with multiple nonpruritic subcutaneous nodules measuring up to 1.8 cm on the left forearm. An excision was performed, and histopathologic evaluation demonstrated a well-circumscribed intravascular lesion composed of a dense lymphoplasmacytic infiltrate among histiocytes and eosinophils. There was no significant surrounding inflammation in the subcutaneous adipose tissue. Further evaluation with immunohistochemistry and special stains did not reveal any hematolymphoid neoplasm or infectious etiology but did reveal >200 polytypic IgG4+ plasma cells per high-powered field and an IgG4:IgG ratio of >0.5, supporting a diagnosis of IgG4-related disease with obliterative phlebitis of a medium-sized subcutaneous vein. This presentation expands the current classification of cutaneous IgG4-related disease and highlights the need for broader recognition of vascular and clinical manifestations in this disease spectrum.