Immunoglobulin-G4-related skin disease.

Immunoglobulin-G4-related disease (IgG4-RD) is an autoimmune-mediated spectrum of diseases, characterized by infiltration of IgG4+ plasma cells into one or multiple organs, with the pancreas being the most commonly affected organ. The disease mostly affects middle-aged to elderly men. Diagnosis requires an integration of clinical, radiologic, pathologic, and serologic studies. Histologically, there is an increased infiltration of IgG4+ plasma cells, elevated ratio of IgG4+/IgG plasma cells of more than 40%, and a storiform pattern of fibrosis. There may be eosinophilia, along with elevated IgG4 levels. IgG4-RD can mimic several diseases and should be differentiated from inflammatory and neoplastic processes. Recently, there has been increased awareness of cutaneous involvement by IgG4-RD either as an isolated lesion or primary involvement or as a secondary involvement from a systemic disease. Clinically, cutaneous IgG4+-related disease presents as papules, plaques, and nodules involving the head and neck areas. We have provided a systematic review of the literature of this new and challenging entity of cutaneous IgG4-RD.