AB1018 TREATMENT RESPONSE OF HYDRONEPHROSIS ASSOCIATED WITH IDIOPATHIC RETROPERITONEAL FIBROSIS, FOCUSING ON RATIO OF IgG4/IgG3 SERUM CONCENTRATION

Background: Hydronephrosis, a common complication of idiopathic retroperitoneal fibrosis (iRPF), may lead to poor renal outcomes unless it is resolved. Pathological confirmation can help to identify the aetiology of the disease and determine the treatment strategy. But, in most cases, it is difficult to obtain sufficient tissue due to the location of fibrosis. In a recent study, parts of iRPF are correlated with IgG4-related disease characterised by elevated serum IgG4 levels (>135 mg/dL). Normal serum IgG3 level (21–176 mg/dL) has been known to be higher than normal serum IgG4 level (4–86 mg/dL). The reverse IgG4/IgG3 ratio has been suggested to be an IgG4-related disease component that distinguishes it from primary sclerosing cholangitis [1]. However, the ratio of IgG3 and IgG4 may be reversed in iRPF patients with hydronephrosis. Objectives: We aimed to investigate the ratio of IgG subclasses as a predictive factor associated with treatment response of hydronephrosis in patients with iRPF. Methods: We retrospectively recruited 19 iRPF patients with hydronephrosis who evaluated serum IgG subclasses in a tertiary hospital between 2004 and 2019. Hydronephrosis was evaluated on the basis of imaging findings. Medications and clinical and laboratory findings, including IgG subclasses, were reviewed following the diagnosis of hydronephrosis. Hydronephrosis improvement on subsequent images was evaluated to assess treatment response. Categorised data were compared using chi-square or Fisher’s exact test. Continuous variables were compared using Mann–Whitney U test. Results: At baseline, median serum IgG3 and IgG4 levels were 64 (IQR 37–82) mg/dL and 71 (IQR 40–171) mg/dL. Five patients had serum IgG4 levels > 135 mg/dL and 11 patients had the reverse serum level of IgG4/IgG3. On subsequent images (median follow-up at 3.2 [IQR 1.7–4.0] months), 11 patients showed hydronephrosis improvement. The proportions of positive ratio of serum IgG4/IgG3 (81.8% vs. 25%, p = 0.024), periaortic involvement (81.8% vs. 25%, p = 0.024) and high-dose glucocorticoid treatment (45.5% vs. 0%, p = 0.045) were significantly higher in patients with improvement than in those without improvement (Table 1). Interestingly, even in cases with normal serum IgG4 levels, patients with improvement showed a higher serum IgG4/IgG3 ratio than in those without improvement (median 1.5 vs. 0.7, p = 0.038). Conclusion: The reverse ratio of serum IgG4/IgG3 was associated with hydronephrosis treatment response, thus suggesting favourable responses to high-dose corticosteroid. References: [1]Boonstra K, Culver EL, de Buy Wenniger LM, et al. Serum immunoglobulin G4 and immunoglobulin G1 for distinguishing immunoglobulin G4-associated cholangitis from primary sclerosing cholangitis. Hepatology 2014;59:1954-63. Disclosure of Interests: None declared