MEMBRANOPROLIFERATIVE GLOMERULONEPHRITIS WITH SEVERE ENDOTHELIAL INJURY AND UNCLASSIFIED STRIATED ELECTRON-DENSE DEPOSITS IN AN ELDERLY WOMAN

Membranoproliferative glomerulonephritis (MPGN) represents a histopathological pattern encompassing diverse etiologies. Accurate diagnosis requires correlation of clinical findings with renal biopsy, including immunofluorescence (IF) and electron microscopy (EM). In elderly patients presenting with nephrotic syndrome and MPGN lesions, secondary causes such as infection- or hematologic disorder–associated glomerular diseases must be carefully assessed and differentiated, as appropriate diagnosis and treatment are critical for prognosis. We report an elderly woman with MPGN exhibiting unique striated electron-dense deposits (EDD) and severe endothelial injury that rapidly progressed to end-stage renal disease (ESRD). 

Clinical, hematological, and urine data for a 79-year-old woman were collected. Kidney biopsy (LM, IF, EM) was performed for definitive diagnosis. Immunofixation electrophoresis, urinary Bence Jones protein (BJP) studies, and bone marrow aspiration were conducted to rule out hematologic disorders. Pathological tissues were analyzed using LM, IF, and special stains (Congo red, light chain, PAL-E). Mass spectrometry is planned to characterize the molecular composition of the deposits. The patient had persistent proteinuria and hematuria for two years, followed by nephrotic-range proteinuria and worsening renal function.

On admission, urinary protein was 9.7 g/gCr, sCr 2.39 mg/dL, and serum albumin 2.6 g/dL, consistent with nephrotic syndrome and progressive renal impairment. Serological testing for autoantibodies, cryoglobulins, and viral infections including hepatitis was negative. Immunofixation electrophoresis and urinary BJP studies detected no monoclonal proteins. Renal biopsy revealed diffuse mesangial proliferation and irregular double-contoured glomerular basement membranes consistent with an MPGN pattern, accompanied by focal capillary microaneurysms. IF showed only weak, nonspecific deposition of immunoglobulins and complements, with no evidence of immune-complex or complement-mediated MPGN. Segmental positivity for pathologische anatomie Leiden-endothelium (PAL-E), a marker of endothelial injury, was observed within glomerular capillaries. EM demonstrated marked subendothelial widening with fibrin deposition and distinctive striated fibrillar EDD. Congo red staining was negative, and light chain staining showed a polyclonal pattern. Because urinary BJP had been transiently positive at a previous hospital, bone marrow aspiration was performed, but no hematologic disorder was identified. Despite strict blood pressure control and conservative therapy for chronic kidney disease, renal function progressively declined, and maintenance hemodialysis was initiated 18 months after biopsy. 

This case of MPGN with severe endothelial injury and unique striated EDDs progressed rapidly to ESRD. The ultrastructural pattern did not correspond to known organized deposit diseases such as fibrillary or immunotactoid glomerulopathy, suggesting an unclassified disease entity. Similar cases with comparable periodic structures have been sporadically reported, mainly from Japan, implying a distinct but poorly defined subtype within the MPGN spectrum. Mass spectrometry will be performed to characterize the molecular composition of the deposits and compare them with previously reported cases. This case underscores the importance of EM and proteomic approaches for elucidating atypical MPGN lesions and expanding our understanding of glomerular diseases with organized deposits.