Background IgG4-related kidney disease is a major manifestation of IgG4-related disease, a systemic fibroinflammatory disorder. However, the clinical and prognostic kidney-related factors in patients with IgG4-related kidney disease are insufficiently defined. Methods We conducted an observational cohort study using data from 35 sites in two European countries. Clinical, biologic, imaging, and histopathologic data; treatment modalities; and outcomes were collected from medical records. Logistic regression was performed to identify the possible factors related to an eGFR ≤30 ml/min per 1.73 m 2 at the last follow-up. Cox proportional hazards model was performed to assess the factors associated with the risk of relapse. Results We studied 101 adult patients with IgG4-related disease with a median follow-up of 24 (11–58) months. Of these, 87 (86%) patients were male, and the median age was 68 (57–76) years. Eighty-three (82%) patients had IgG4-related kidney disease confirmed by kidney biopsy, with all biopsies showing tubulointerstitial involvement and 16 showing glomerular lesions. Ninety (89%) patients were treated with corticosteroids, and 18 (18%) patients received rituximab as first-line therapy. At the last follow-up, the eGFR was below 30 ml/min per 1.73 m 2 in 32% of patients; 34 (34%) patients experienced a relapse, while 12 (13%) patients had died. By Cox survival analysis, the number of organs involved (hazard ratio [HR], 1.26; 95% confidence interval [CI], 1.01 to 1.55) and low C3 and C4 concentrations (HR, 2.31; 95% CI, 1.10 to 4.85) were independently associated with a higher risk of relapse, whereas first-line therapy with rituximab was protective (HR, 0.22; 95% CI, 0.06 to 0.78). At their last follow-up, 19 (19%) patients had an eGFR ≤30 ml/min per 1.73 m 2 . Age (odd ratio [OR], 1.11; 95% CI, 1.03 to 1.20), peak serum creatinine (OR, 2.74; 95% CI, 1.71 to 5.47), and serum IgG4 level ≥5 g/L (OR, 4.46; 95% CI, 1.23 to 19.40) were independently predictive for severe CKD. Conclusions IgG4-related kidney disease predominantly affected middle-aged men and manifested as tubulointerstitial nephritis with potential glomerular involvement. Complement consumption and the number of organs involved were associated with a higher relapse rate, whereas first-line therapy with rituximab was associated with lower relapse rate. Patients with high serum IgG4 concentrations (≥5 g/L) had more severe kidney disease.
IgG4-related disease (IgG4-RD) is a recently recognized multisystem disease characterized by lymphoplasmacytic inflammation and fibrosis in affected tissues that can affect several organs including the kidney, the involvement of which is often manifested by tubulointerstitial nephritis. The pathogenic mechanisms of IgG4-RD are divided into two sections: one focused on potential initiation mechanisms, particularly genetic, and the other on specific pathological pathways. For the specific pathological pathways, cellular immunity, particularly T-cell mediated immunity, has been implicated in the pathogenesis of IgG4-RD. Renal involvement may manifest as an intrinsic IgG4-related kidney disease (IgG4-RKD) or as a consequence of ureteric obstruction from retroperitoneal fibrosis. Intrinsic kidney disease is most commonly a tubulointerstitial nephritis, but may also present with a variety of glomerular lesions, in particular membranous nephropathy. The first-line treatment of IgG4-RKD is steroids. The long-term side effects of corticosteroids including diabetes, relapses, and resistance to corticosteroid therapy have prompted some experts to use immunosuppressive agents such as rituximab. However, the pathogenesis remains poorly understood. As any delay in treatment may result in irreversible renal failure, early diagnosis and appropriate therapy are very important. Randomized studies are needed to confirm the efficacy of immunosuppressants such as rituximab.
