PMC8313325_01
Renal biopsy findings. (a) One glomerulus showing segmental endocapillary hypercellularity, karyorrhectic nuclear debris, and a small cellular crescent (periodic acid-Schiff; original magnification: 400x). (b) Nearly, all of the remaining glomeruli demonstrate no significant abnormalities (periodic acid-Schiff; original magnification: 200x). (c) Immunofluorescence for IgG reveals diffuse, global, linear staining within the glomerular basement membrane (original magnification: 200x). (d) Widespread, subtle subendothelial widening is noted on electron microscopy, without the presence of any immune deposits (original magnification: 4800x).
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fig1
Deeper level sections disclosed a single glomerulus with segmental endocapillary hypercellularity, karyorrhexis, and a small cellular crescent (Figure 1(a)). Aside from these glomerular changes, the remaining glomeruli appeared unremarkable (Figure 1(b)). Immunofluorescence revealed strong, diffuse, global, linear glomerular basement membrane staining for IgG as well as moderate kappa and lambda light chain staining in the same pattern (Figure 1(c)). Electron microscopy disclosed widespread mild subendothelial widening, without the presence of electron-dense immune deposits (Figure 1(d)).
Degree of proteinuria and antiglomerular basement membrane (anti-GBM) antibody levels during the course of illness. Spot urine protein-to-creatinine ratio (solid line) and anti-GBM antibody levels (dotted line) are shown relative to the time of biopsy. *Limit of detection for anti-GBM antibody levels is 1.0 AI, which has remained <1.0 AI since day 43. **Limit of detection for urine protein-to-creatinine ratio is 0.19, which has remained between <0.19 and 0.25 since day 64. Data extend to day 334 at the latest follow-up. Length of treatment is indicated by black bars below the X-axis.
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fig2
One week after receiving the fourth and final rituximab dose, the patient's anti-GBM antibody titers became undetectable and has stayed negative to date (Figure 2). Furthermore, one month after completing the rituximab course, the patient's proteinuria completely resolved and has remained negative to date (Figure 2).