Background IgG4-related kidney disease (IgG4-RKD) is a comprehensive term for renal lesions associated with IgG4-related disease . IgG4-RKD is frequently complicated by hypocomplementemia [1, 2, 3], but its clinical significance and mechanisms have not been clarified.
Objectives This study aimed to investigate clinical features of IgG4-RKD patients with hypocomplementemia compared with those without it, leading to clarification of the clinical significance and mechanisms of hypocomplementemia.
Methods We extracted 25 patients with IgG4-RKD between September 2005 and December 2016 in our hospital. Based on the presence/absence of hypocomplementemia at diagnosis, we divided them into a hypocomplementemia group (n=11) and normal complement group (n=14), and retrospectively analyzed various clinical features (age, sex, serum IgG levels, serum IgG4 levels, gaps between serum IgG and IgG4 level, ratio of serum IgG to serum IgG4, serum IgG subclasses, serum IgE levels, serum creatinine levels, urinary protein and urinary occult blood, urinary β2-microglobulin, urinary N-acetyl-β-D-glucosaminidase, initial dose of prednisolone, serum IL-2R levels, multiple organ lesion) during the clinical course in the two groups.
Results The patients comprised 18 men and 7 women with an average age of 67.5 years (range, 44 to 81 years). Serum IgG levels (3971±729 mg/dL vs. 2157±598 mg/dL; p<0.001), gaps between serum IgG and IgG4 level (2992±770 mg/dL vs. 1482±444 mg/dL; p<0.001), serum IgG1 levels (2043±1025 mg/dL vs. 891±209 mg/dL; p=0.017), and the number of involved organs (4.1±1.1 vs 2.9±1.1; p=0.018) were significantly different between the two groups, while serum IgG4 levels (979±477 mg/dL vs. 791±575 mg/dL; p=0.298) and serum creatinine levels (1.96±1.89 mg/dL vs. 1.09±0.48 mg/dL; p=0.298) were not. At relapse of renal lesions, although both groups showed serum IgG4 re-elevation, the hypocomplementemia group showed exacerbation of hypocomplementemia and re-expansion of gaps between serum IgG and IgG4 level, while the normal complement group did not.
Conclusions Hypocomplementemia may be associated with multiple organ involvement and elevation of IgG subclasses other than IgG4 including IgG1 in IgG4-RKD. In patients who initially show hypocomplementemia, a decline in serum complement levels implies renal lesion relapse.
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Disclosure of Interest None declared