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"Renal rim sign": a diagnostic radiological sign of IgG4-related tubulointerstitial nephritis?

A 61-year-old Japanese man presented with bilateral submandibular and parotid gland swelling for a year following sicca symptoms. Results of renal function tests were normal, with a creatinine level of 0.75 mg/dL and a serum urea nitrogen level of 20.7 mg/dL. Urinalysis was negative for protein and blood and showed normal sediment. In addition, urine levels of >1-microglobulin and A2-microglobulin were also normal. Results from serological tests including antiYnuclear antibody, antiSSA, and SSB antibodies were negative. Total immunoglobulin (Ig) G was 3233 mg/dL, and IgG4 level was 2120 mg/dL. Computed tomographic (CT) scan with contrast showed bilateral kidney swelling with multiple low-attenuated mass-like lesions and a soft tissue rim around the kidneys, which was better identified with enhanced magnetic resonance imaging (MRI; Figure A, B). FluorodeoxyglucoseYpositron emission tomography showed intense uptake in submandibular glands, hilar nodes, and bilateral kidneys. Renal and submandibular biopsy revealed interstitial fibrosis with IgG4-positive plasma cell infiltration. The CT findings of the kidneys improved dramatically after corticosteroid therapy. Immunoglobulin G4Yrelated disease is a recent identified clinical entity that is characterized by elevated serum IgG4, IgG4-positive plasma cell infiltration, and fibrosis in the affected tissues such as the salivary and lacrimal glands (Mikulicz disease), pancreas (autoimmune pancreatitis), retroperitoneum (retroperitoneal fibrosis), periaorta (periaortitis), and bile duct (sclerosing cholangitis). The CT findings of IgG4-related tubulointerstitial nephritis often show multiple low-attenuated nodules