IgG4-related periaortitis presenting as left flank pain

We present the case of periaortitis which presented initially with left flank pain. A diagnosis of IgG4-related disease (IgG4-RD) was subsequently made and managed as such. IgG4-RD is rare, can be difficult to diagnose, and requires clinical, serological, radiological and pathological correlation, particularly given that serum IgG4 levels may be normal. Immunosuppression is the mainstay treatment for this chronic condition alongside regular rheumatology input.