Hypocomplementemia is related to elevated serum levels of IgG subclasses other than IgG4 in IgG4-related kidney disease.

OBJECTIVES: This study investigated the clinical features of IgG4-RKD patients with hypocomplementemia compared with those without it, so as to clarify the factors related to hypocomplementemia. METHODS: In this single-center retrospective study, we analyzed the clinical features of 25 patients with IgG4-RKD according to the presence/absence of hypocomplementemia. Additionally, we validated the results of a single-center study in a separate large multicenter cohort of 328 patients with IgG4-RD, and searched for factors related to hypocomplementemia. RESULTS: Serum IgG levels (p < .001), non-IgG4 IgG levels, calculated as the total IgG minus IgG4 (p < .001), serum IgG1 levels (p = .017), and the number of involved organs (p = .018) were significantly higher in the hypocomplementemia group. At relapse of renal lesions in four patients, all had serum IgG4 re-elevation, with the three with hypocomplementemia presenting worsening of hypocomplementemia and re-elevation of non-IgG4 IgG levels. In a validation cohort of 328 patients with IgG4-RD, multivariate logistic regression analysis indicated elevation of non-IgG4 IgG levels to be an independent factor related to hypocomplementemia in the patients with IgG4-RKD. CONCLUSION: The present study suggests that hypocomplementemia is associated with elevation of IgG subclasses other than IgG4 including IgG1 in IgG4-RKD.

Different factors underlie recurrent and de novo organ involvement in immunoglobulin G4-related disease.

OBJECTIVES: In IgG4-related disease (IgG4-RD), relapse including recurrent organ involvement (ROI) and de novo organ involvement (DNOI) occurs frequently during the clinical course. This study aimed to clarify the differences between the risk factors underlying ROI and DNOI in IgG4-RD. METHODS: We retrospectively investigated factors related to ROI and DNOI in 86 IgG4-RD patients. For assessment of factors related to ROI and DNOI, we performed uni- and multivariate Cox regression analyses. On stepwise multivariate analysis, we applied the variables with P < 0.1 in the univariate analysis and the predictors of relapse suggested in past reports. RESULTS: During the mean follow-up period of 63.1 months, ROI was detected at 1.0-120 months after diagnosis in 20 patients, 4 of whom were not receiving glucocorticoid (GC) at the time of ROI. In contrast, DNOI was detected at 5.0-120 months after diagnosis in 15 patients, 8 of whom were not receiving GC at the time of DNOI. In the multivariate analysis, blood eosinophil counts at diagnosis [per 100/µl; hazard ratio (HR) 1.072 (95% CI 1.018, 1.129)] and continuation of GC [vs discontinuation or observation without GC; HR 0.245 (95% CI 0.076, 0.793)] had a significant impact on the time to DNOI, whereas age [HR 0.942 (95% CI 0.899, 0.986)] and ANA positivity [vs negativity; HR 6.632 (95% CI 1.892, 23.255)] had a significant impact on the time to ROI. CONCLUSION: The present study suggests that the risk factors of ROI and DNOI are different in IgG4-RD, highlighting the need for different preventative strategies.