PMC10085645_01
Histopathologic findings on kidney biopsy. (a) Moderate interstitial fibrosis and tubular atrophy throughout cortex (masson trichrome stain, 20x magnification, scale bar = 500 mum). (b) Unremarkable glomerulus (periodic acid Schiff stain, 400x magnification, scale bar = 20 mum). (c) Interlobular artery with severe intimal fibrosis (SMMT stain, 400x magnification, scale bar = 20 mum). (d) Neutrophil-rich infiltrate within tubulointerstitium (hematoxylin and eosin stain, 200x magnification, scale bar = 50 mum). (e) Neutrophilic tubulitis (jones methenamine silver stain, 600x magnification, scale bar = 20 mum). (f) Mixed interstitial inflammation with lymphocytes, plasma cells, eosinophils, histiocytes, and focal neutrophils (hematoxylin and eosin stain, 600x magnification, scale bar = 20 mum). (g) Lymphocytic tubulitis (jones methenamine silver stain, 400x magnification, scale bar = 20 mum). (h) Linear IgG staining along proximal tubular basement membranes (fluorescein-conjugated antihuman IgG stain, 100x magnification, scale bar = 100 mum), with lack of staining along glomerular basement membranes. (i) Linear IgG staining along proximal tubular basement membranes (fluorescein-conjugated antihuman IgG stain, 100x magnification, scale bar = 100 mum).
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fig1
There was patchy, but dense neutrophil-rich interstitial inflammation accompanied by neutrophilic rimming along the tubules and white blood cell casts (Figure 1).
Computerized tomography of the abdomen and pelvis without contrast demonstrating bilateral perinephric stranding (red arrows), consistent with acute pyelonephritis.
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fig2
IgG and C3 staining (3+ each) along the proximal tubular basement membranes without associated glomerular or distal tubular epithelial staining (Figure 2). IgG subclass staining revealed staining for all IgG subclasses along the TBMs (3+ each for IgG1, IgG2, IgG3, and IgG4). The CT scan of the abdomen and pelvis without contrast was suggestive of pyelonephritis, as it had stranding in the perinephric space (Figure 2).