Membranous glomerulonephritis in diabetic patients: a study of 15 cases and review of the literature.

Glomerular diseases other than diabetic glomerulosclerosis (DGS) occurring in diabetic patients may pose a diagnostic challenge to both clinicians and pathologists. We studied 15 cases of membranous glomerulonephritis (MG) in patients with diabetes mellitus focusing on the morphologic changes of the kidney. Light microscopic observation revealed nodular and/or diffuse DGS in 12 cases and no DGS in three. Periodic acid-silver methenamine stain showed spikes or chain-like structures in the glomerular capillary wall in 13 cases, indicating the presence of MG. Ultrastructurally, MG was classified into Stage I (N = 2), II (N = 8), III (N = 4), or IV (N = 1). Six out of nine cases with Stages I and II MG showed a thickened lamina densa of the glomerular basement membrane (GBM), suggesting diabetic influence on the GBM. Moreover, MG in some of the cases suggested atypical ultrastructural features including (a) the presence of large immune type deposits separated by tall spikes (N = 4), (b) high electron density of deposits in spite of their intramembranous location (N = 4), and (c) the presence of immune type deposits of mesangial (N = 3) and subendothelial (N = 2) locations. It is postulated that these atypical features are caused by altered turnover of the GBM, impaired glomerular clearance of immune complexes, changes of the glomerular capillary wall as the result of hemodynamic alterations, and/or nonenzymatic glycosylation in diabetic milieu.