Immune-complex glomerulonephritis in cats: a retrospective study based on clinico-pathological data, histopathology and ultrastructural features.

Background: Chronic kidney disease (CKD) has typically a non-immune mediated origin in cats and immune-complex glomerulonephritis (ICGN) is scarcely described. Aims of this study were to characterize ICGN by light and electron microscopy and identify associations with clinico-pathological findings. In addition, comparisons between cats with ICGN and non immune-complex glomerulonephritis (non-ICGN) were performed. Renal samples examined between 2010 and 2019 were considered if both light and electron microscopy were performed. Signalment, feline immunodeficiency virus (FIV) and leukemia virus (FeLV) status, serum creatinine concentration, urine protein-to-creatinine (UPC) ratio, systolic blood pressure (SBP) and International Renal Interest Society (IRIS) stage were retrieved and used for comparisons.

Results: Sixty-eight client-owned cats were included. Thirty-seven cats (54.4%) had ICGN and 31 (45.6%) non-ICGN. Eighteen (48.6%) with ICGN had membranous glomerulonephropathy (MGN), 14 (37.8%) membranoproliferative glomerulonephritis (MPGN), and 5 (13.5%) mesangioproliferative glomerulonephritis (MeGN). Clinico-pathological data were not associated with any type of ICGN. Among cats with non-ICGN, 11 (35.5%) had end-stage CKD, 9 (29%) focal segmental glomerulosclerosis, 6 (19.4%) global and multifocal mesangiosclerosis, 2 (6.5%) glomerular atrophy, 2 (6.5%) renal dysplasia and 1 (3.1%) amyloidosis. Eight (25.8%) cats with non-ICGN had chronic interstitial nephritis (CIN) grade 1, 13 (41.9%) grade 2 and 10 (32.3%) grade 3; creatinine and UPC ratio increased with CIN grades (p = 0.001, p < 0.001). Cats with ICGN were more frequently FIV or FeLV-infected (OR:11.4; 95%CI:1.4-94.4; p = 0.024), had higher UPC ratio (OR:6.8; 95%CI:2.5-18.2; p < 0.001) and were younger (OR:0.9; 95%CI:0.7-1.0; p = 0.042) than cats with non-ICGN.

Conclusions: MGN and MPGN were the most common morphological diagnoses of ICGN in cats. Unfortunately, none of the investigated findings differentiated ICGN morphological diagnoses. Serum creatinine concentration and UPC ratio were directly associated with grades of CIN (p = 0.001 and p < 0.001, respectively), confirming previous literature. More ICGN than non-ICGN was observed in cats with retroviral infections, younger cats and higher UPC ratio.