IgG4-related kidney disease and retroperitoneal fibrosis: An update.

The most representative kidney lesion of IgG4-related disease (IgG4-RD) is plasma cell-rich tubulointerstitial nephritis (TIN) with distinctive imaging findings including multiple low-density lesions on contrast-enhanced computed tomography. In addition, membranous glomerulonephritis is a representative glomerular lesion of this disease. Recent advances have clarified that inflammation with IgG4-positive plasma cell infiltrates is not restricted to the renal parenchyma, but can be seen in outside the renal capsule, around medium-sized arteries such as lobar arteries, around nerves, and in the renal pelvis and periureter. Hypocomplementemia is a very important feature of IgG4-TIN, and serum complement level might serve as a convenient biomarker to predict relapse. Although good responsiveness to glucocorticoid has been considered characteristic of IgG4-RD, delayed start of treatment is associated with partial scarring in the kidneys on imaging study. Therefore, steroid therapy should be immediately initiated as soon as the diagnosis of IgG4-TIN is made. Future analyses of pathogenesis will be needed to more precisely define the optimal therapeutic strategies for the various subsets of Ig4-RD patients.