Acute Kidney Injury and Proteinuria in a Patient With Diabetes and a Submandibular Mass

(A) Dense interstitial inflammatory infiltrate and edema expand the interstitium. The glomerulus shows thickened peripheral capillary walls (periodic acid–Schiff stain; original magnification ×200). (B) The majority of cells within the inflammatory infiltrate are plasma cells (periodic acid–Schiff stain). (C) CD138 immunoperoxidase stain highlights the large number of plasma cells within the interstitial infiltrate. (D) Approximately half the plasma cells are positive on immunoglobulin G4 immunoperoxidase stain (original magnification ×400).

Direct immunofluorescence shows strong granular glomerular peripheral capillary wall staining for (A) immunoglobulin G (IgG) and (B) C3. There is also strong granular staining of Bowman capsule and tubular basement membranes for both (A) IgG and (B) C3 (original magnification: [A] ×400, [B] ×250). (C) Electron microscopy shows subepithelial electron-dense deposits (arrows) with basement membrane spike formation (original magnification ×30,000). (D) Electron-dense deposits are present within thickened tubular basement membrane (arrows) (original magnification ×40,000). Abbreviation: T, tubular epithelial cell.

Second kidney biopsy specimen. (A) Note the broad stripe of interstitial fibrosis and tubular atrophy in the bottom half of the core, contrasting with well-preserved cortex at the top (periodic acid–Schiff stain; original magnification ×100). (B) Note very sparse positive cells within the interstitial infiltrate on immunoglobulin G4 immunoperoxidase stain (arrows) (original magnification ×400). (C) Direct immunofluorescence shows persistence of strong granular staining for C3 in glomerular peripheral capillary walls (g), Bowman capsule, and tubular basement membranes (original magnification ×200).