CRP and immunoglobulin G4-related sclerosing disease: Although IL-6 immunostaining and serum IL-6 and CRP levels are reportedly useful for distinguishing between IgG4-RD and MCD [20]-[21], some researchers have suggested that IgG4-RD and MCD constitute potentially overlapping disease entities, and have alluded to an “MCD-like” subtype of IgG4-RD [7, 22].