#1297 Approaches to renal response assessment in rare monoclonal immunoglobulin related glomerulopathies
Authors: Khrabrova Maria , Dobronravov Vladimir 
Published: May 2024

Abstract

Background and Aims
AL-amyloidosis (AL) and monoclonal immunoglobulin (MIg) deposition disease are common types of MIg-related glomerulopathies (MIgG) and are well-studied including approaches to treatment and hematological and renal responses (RR) assessment. Other rare MIgG comprise very diverse patterns of glomerular injury e.g. proliferative glomerulonephritis with MIg deposition (PGNMID), C3-glomerulopathy, fibrillary glomerulonephritis etc. Although RR defined as decrease in 24 h proteinuria by 30% without kidney function decline was validated only for renal AL it is widely used for MIg deposition disease and rare MIgG without validation. Nevertheless, the best approach to RR assessment in rare MIgG is still unclear. To shed some light on this problem we performed this study.

Method
We retrospectively analyzed 31 patients with rare MIgG who were treated with clone-specific treatment and had available follow-up (FUP) ≥6 months (mo). The following morphological patterns were diagnosed: PGNMID (n = 9), C3-glomerulopathy (n = 9), thrombotic microangiopathy (n = 5), cryoglobulinemic glomerulonephritis (n = 3), fibrillary glomerulonephritis (n = 3), immunotactoid glomerulonephritis (n = 1) and membranous nephropathy (n = 1). Patients’ baseline parameters are shown on Fig. 1 as well as treatment modalities. Hematological response defined according to currently accepted criteria is demonstrated on Fig. 1. We evaluated two approaches to the RR assessment: 1) at least partial renal response (PR) defined as 24 h proteinuria decreased by 50% from the baseline and &lt;3.5 g, and 2) according to Palladini's criteria for AL (AL-RR) i.e. 24 h proteinuria decreased by 30% from the baseline or &lt;0.5 g. Both RR were considered as achieved only in the absence of estimated glomerular filtration rate (eGFR) decline &gt;25%. Time points for RR assessment were 6, 12 and 24 mo from the clone-specific treatment initiation. Renal outcome was estimated as initiation of renal replacement therapy or eGFR &lt;15 ml/min/1.73 m2 at the end of follow-up. Death-censored renal survival was analyzed by the Kaplan-Meier method. Cox regression analysis was applied to determine which RR was independently associated with long-term kidney outcome. P-value was assumed at &lt;0.05. Median FUP was 19 (7; 50) mo. FUP ≥12 and ≥24 mo were available in 26 and 17 patients, respectively.

Results
Total number of patients who achieved AL-RR at any RR assessment time point was 22 (71%). At 6, 12 and 24 mo the achievement of AL-RR was registered in 17, 16 and 10 patients, respectively. PR cumulatively was achieved in 19 (61%) patients: at time points of 6, 12, and 24 mo it was registered in 14, 14 and 9 cases, respectively. The 5-year cumulative renal survival in those who had AL-RR was better than in not responders (Fig. 2A). Patients who ever achieved PR had better cumulative renal survival compared with patients with no renal remission (Fig. 2B). In univariate Cox regression analysis the achievement of AL-RR (Exp(β) 0.158 (95% CI 0.03; 0.819)) was associated with renal outcome as well as the achievement of PR (Exp(β) 0.074 (95% CI 0.09; 0.626)). In multivariate Cox regression model adjusted for eGFR at the time of kidney biopsy AL-RR vs no response was estimated as an independent predictor of renal long-term prognosis (Exp(β) 0.082 (95% CI 0.009; 0.725)) as well as eGFR (Exp(β) 0.89 (95% CI 0.821; 0.985)). The only independent predictor of renal outcome in the model including eGFR at the time of kidney biopsy (Exp(β) 0.85 (95% CI 0.72; 0.99), p = 0.05) was PR (Exp(β) 0.011 (95% CI 0; 0.547), p = 0.021).

Conclusion
The classical concept of complete and partial renal remission seems to be more appropriate for rare MIgG and requires further validation studies.