SO058IGG4-RELATED KIDNEY DISEASE : A FRENCH NATIONWIDE RETROSPECTIVE COHORT STUDY
Authors: Chaba Anis , Zaidan Mohamad , Jean Jacques BOFFA , Alexandre KARRAS , Vincent Audard , RENAUD SNANOUDJ , Thaunat Olivier , NOUVIER Mathilde , Arnaud DEVRESSE , Joly Dominique , Halimi Jean Michel , CARTERY CLAIRE , Daugas Eric , Peraldi Marie-Noelle , Mathieu LEGENDRE , Julie BELLIERE , Faguer Stanislas , Dimitri TITECA , William HANF , Petitclerc Thierry , Guillaume HANOUNA , Chemouny Jonathan , Nabila GOUMRI , Simon DUQUENNOY , Vilaine Eve 
Published: June 2020

Abstract

Background and Aims
IgG4 disease is a systemic fibroinflammatory disorder that may affect virtually any organ. IgG4-related kidney disease (IgG4-RKD) is a major manifestation, occurring in almost one third of patient. The present study addresses the diagnosis, management and outcome of French patients with IgG4-RKD.

Method
We conducted a retrospective observational study including patients with renal impairment due to IgG4-RKD from 32 centers. Clinical, biological, and imaging data, as well as management modalities and outcome, were retrieved from medical records.

Results
74 patients, 64 males and 10 females, were diagnosed with IgG4-RKD between 1997 and 2019 and were included in the present study. The mean age at diagnosis was 65.2 ± 15-year-old. Renal involvement was present at diagnosis in 63% of cases. Nine (12%) patients had isolated renal involvement, whereas extra-renal involvement included retroperitoneal fibrosis (20%), auto-immune pancreatitis (49%), cholangitis (27%), and lung disease (22%). Renal imaging lesions were observed in 48 (64%) patients, and included renal hypertrophy, patchy lesions and pseudo-tumor solitary renal lesion. PET-CT scan was performed in 47 (65%) patients and showed hypermetabolic renal lesion(s) in 36% of cases. The presence of extra-renal hypermetabolic lesions was observed in 35 cases (74%). 43 %, 25% and 14% of patients presented with AKI, AKI-on-CKD, and isolated CKD, respectively. The mean serum creatinine level at diagnosis was 244 ± 140 µmol/L, corresponding to an eGFR of 69 ± 22ml/min/1.73m. Urinary sediment was most often bland. Mean urine protein-to-creatinine ratio was 1.27 g/g. of note, 26% of patients had more than 1 g/g. 82% of patients underwent a kidney biopsy showing tubulointerstitial involvement in all cases, 12 (16%) had additional glomerular involvement, mainly membranous nephropathy. The major additional laboratory abnormalities included polyclonal hypergammaglobulinemia, and increased serum IgG4 increase in 83% and 86%, respectively. Complement levels were decreased in 27 (37%) patients. Two patients were lost for follow-up and 69 patients were treated with corticosteroid therapy in 66 (89%) patients and 10 received Rituximab as first line therapy. The mean duration of follow-up was 28.8 ± 30 months. During follow-up, 22 (30%) patients relapsed, while 45 (62%) patients had persistent CKD at last follow-up, with a mean eGFR of 47±27 ml/min/1.73m. Seven (9%) patients progressed to ESRD and 7 died.
A significant response was achieved in 46 (62%) patients. Patients who received steroids higher than 0.5mg/kg/day had lower serum IgG4 levels (1.8 g/l versus 5.7 g/l, p=0.007) at last follow up but there was no significant difference observed in terms of renal function between the two groups (45.5 vs 48.8 ml/min/1.73m, p= 0.72). By univariate analysis, predictors of relapse were low C3 or C4 serum level (p=0.01), ANCA positivity (p= 0.02), renal radiological lesions (p=0.05). At last follow-up the eGFR was worse in patients with a serum creatinine diagnosis greater than 300 µmol/L (30.25 vs 57 ml/min/1.73m p=0.0001) and more progressed to ESRD (p=0.03).

Conclusion
IgG4-RKD has been recently described and may affect middle-aged males. The disease presents as tubulointerstitial nephritis with glomerular involvement in 16% of cases. Disease response to corticosteroid therapy is favorable but is characterized by a high rate of relapses and a significant risk of persistent CKD in the majority of patient. Risk of ESRD and death in almost 20% of patients.