The effect of fibrinoid necrosis on the clinical features and outcomes of primary IgA nephropathy

Background To explore the clinicopathologic features and outcomes of IgAN patients who presented with fibrinoid necrosis (FN) lesions or not and the effect of immunosuppressive (IS) treatment in IgAN patients with FN lesions as well. Methods This was a retrospective cohort study with 665 patients diagnosed with primary IgAN from January 2010 to December 2020 in Tianjin Medical University General Hospital and having detailed baseline and follow-up characteristics. Patients were divided into two groups depending on the appearance of FN lesions. Patients with FN lesions were recruited into Group FN1, while patients who were not found FN lesions in their renal biopsy specimens were recruited into Group FN0. Compare the differences between Group FN0 and Group FN1 in baseline clinicopathologic features, treatment solutions and follow-up data as well. To evaluate the impact of different fractions of FN lesions on baseline characteristics and prognosis of IgAN, we subdivided patients in Group FN1 into 3 groups depending on the FN lesions distribution, Mild Group: 0 < FN% < 1/16; Moderate Group: 1/16 < FN% < 1/10; Severe Group: FN% > 1/10. Furthermore, we compared the differences in baseline clinicopathologic features, treatment solutions and follow-up data among these three groups. Kidney endpoint event was defined as patients went into end-stage kidney disease (ESKD), which estimated glomerular filtration rate (eGFR) < 15 ml/min/1.73 m^2, regularly chronic dialysis over 6 months or received renal transplantation surgery. The kidney composite endpoint was defined by a ≥ 30% reduction in eGFR, double Scr increase than on-set, ESKD, chronic dialysis over 6 months or renal transplantation. Compare the survival from a composite endpoint rate in different groups by Kaplan-Meier survival curve. The univariate and multivariate Cox models were used to establish the basic model for renal outcomes in patients with FN lesions. Results (1) A total of 230 patients (34.59%) were found FN lesions in all participants. Patients with FN lesions suffered more severe hematuria than those without. On the hand of pathological characteristic, patients with FN lesions showed higher proportions of M1, E1, C1/C2 and T1/T2 lesions compared with those without FN lesions. (2) The 1-year, 3-year, and 5-year survival of the composite endpoint were lower in the FN1 group than FN0 group. (3) After adjusting for clinicopathological variables, the presence of FN lesions was a significantly independent risk factor for composite endpoint. By using multivariate Cox regression analyses, we also found when the fraction of FN lesions exceeded 10%, the risk of progression into composite endpoint increased 3.927 times. Conclusion Fibrinoid necrosis of capillary loops is an independent risk factor of poor renal outcomes. More effective treatment should be considered for those who had FN lesions.