CRP and IgG4-related retroperitoneal fibrosis: While IgG4-RD generally presents with normal CRP levels,[20,21] some forms of IgG4-RD, such as IgG4-related retroperitoneal fibrosis, periaortitis, and inflammatory aortic aneurysms, can present with high serum CRP.[22–24] In this regard, it should be noted that IgG4-related FM can also present with high serum CRP.