Collapsing glomerulopathy is common in the setting of thrombotic microangiopathy of the native kidney

Thrombotic microangiopathy (TMA) is a poorly recognized cause of collapsing glomerulopathy. The frequency and significance of collapsing glomerulopathy associated with renal TMA have not been specifically studied in native kidney biopsy specimens. Here we retrospectively documented clinicopathologic features of 53 patients with histologically proven TMA in the native kidney, with special emphasis on changes due to focal segmental glomerulosclerosis (FSGS). Histological TMA was related to hypertensive nephropathy in 21 patients, genetic complement abnormalities in 9, drugs in 7, and to other causes in 16 patients. Almost half (26 patients) presented with arteriolar, 6 with glomerular, and 21 with mixed TMA. Using the Columbia classification system for the 53 patients with histological TMA, 33 had concurrent FSGS lesions with collapsing glomerulopathy the dominant variant in 19 patients (58% of the FSGS cases), not otherwise specified in 9 patients, cellular in 3, and perihilar or tip lesions in 1 patient each. The presence of FSGS was associated with a poor renal prognosis, with no prognostic difference between collapsing glomerulopathy and other FSGS variants. Thus, collapsing glomerulopathy is frequently found in native kidney biopsies with TMA, suggesting that endothelial injury may play an important role in the pathophysiology of FSGS.