Improved renal function in initial treatment improves patient survival, renal outcomes, and glucocorticoid-related complications in IgG4-related kidney disease in Japan

We aimed to clarify long-term renal prognosis, complications of malignancy, glucocorticoid (GC) toxicity, and mortality in IgG4-related kidney disease (IgG4-RKD). Reviewing the medical records of 95 patients with IgG4-RKD, we investigated clinical and pathological features at baseline and course of renal function, complications of malignancy, GC toxicity, and mortality during follow-up (median 71 months). The standardized incidence ratio (SIR) of malignancy and standardized mortality ratio (SMR) were calculated using national statistics. Factors related to outcomes were assessed by Cox regression analyses. At diagnosis, the median eGFR was 46 mL/min/1.73m2. GC achieved initial improvement. More renal function recovery within 3-month initial treatment occurred in patients with highly elevated serum IgG and IgG4 levels and hypocomplementemia. Sixty-eight percent, 17%, and 3% of the patients had chronic kidney disease (CKD), >30% eGFR decline, and end-stage renal disease, respectively, during follow-up. Age- and sex-adjusted Cox regression analyses indicated that eGFR (hazard ratio [HR] 0.71) and extensive fibrosis (HR 2.58) at treatment initiation had a significant impact on the time to CKD. Ten patients died, and the SMR was 0.94. The SIR of malignancy was 1.52. The incidence rate of severe infection was 1.80/100 person-years. Cox regression analyses showed that the best eGFR within 3 months after treatment initiation were associated with lower mortality (HR 0.67) and fewer severe infections (HR 0.63). This study suggests that more renal function recovery through early treatment initiation may improve patient survival, renal outcomes, and some GC-related complications in IgG4-RKD.