Clinicopathological differences in focal segmental glomerulosclerosis depending on the accompanying pathophysiological conditions in renal allografts

Primary focal segmental glomerulosclerosis (FSGS) is thought to be caused by circulating factors leading to podocytopathy, whereas segmental sclerotic lesions (FSGS lesions) have several causes. We studied the clinicopathological differences of FSGS-lesions in 258 cases of FSGS in renal allografts, depending on the following accompanying pathophysiology: recurrence of primary FSGS, calcineurin inhibitor (CNI)-induced arteriolopathy, antibody-mediated rejection (ABMR), and other conditions. All cases were categorized with the Columbia classification. Recurrent FSGS developed the earliest after transplantation and showed the highest percentage of the collapsing (COL) variant in which collapse of the glomerular capillaries with epithelial hypertrophy was apparent. FSGS accompanying CNI-induced arteriolopathy predominantly developed the not otherwise specified (NOS) variant, showing severe ultrastructural endothelial injury. On the contrary, approximately 7% of the cases showed the COL variant, presenting glomerular endothelial damage such as double contours of glomerular basement membrane and endothelial cell swelling as well as epithelial cell proliferation. FSGS with ABMR had the highest creatinine levels and cellular variant percentage, with marked inflammation and ultrastructural endothelial injury. Approximately two-thirds of the cases without ABMR, CNI-induced arteriopathy, or recurrent FSGS had other coexisting conditions such as glomerulonephritis, T cell-mediated rejection, and reflux nephropathy with progressive tubulointerstitial fibrosis. Most of these cases were of the NOS variant. The clinicopathologic features of post-transplant FSGS differed depending on the associated conditions, and endothelial injury was apparent especially in cases of CNI-induced arteriolopathy and ABMR. Precise observation of FSGS lesions may facilitate the diagnosis and clinical management of FSGS during renal transplantation.