Interstitial Inflammation as a Prognostic Factor in IgA Nephropathy

Viewpoint on:

Zhu B., Liu W.-H., Lin Y., Li Q., Yu D.-R., Jiang F., Tang X.-L., Du Y.-Y., Yin J.-Z., Li X.-F., Zhong Y.-Z., Wang W.-R., Sun Y., Zhang M.-J., Gao Y.-C., Yuan C.-Y., Zhu C.-F., Cheng X.-X.: Renal Interstitial Inflammation Predicts Nephropathy Progression in IgA Nephropathy: A Two-Center Cohort Study. American Journal of Nephrology DOI 10.1159/000524585

Prediction of the long-term outcomes in individual patients with IgA nephropathy (IgAN) using pathological parameters has long been a “holy grail” in Nephrology. To be sure, the addition of the Oxford-MEST-C scoring system and the International IgA Nephropathy Prognosis tool (IgAN-PT) have achieved much in improving the prediction of progressive disease. Pathology, when combined with clinical features, especially persistent proteinuria, offers substantial value to outcome prediction, but there is always room for improvement. The role of the extent and severity of renal interstitial inflammation in independent prediction outcome remains uncertain.

Zhu and coworkers sought to clarify the issue of the prognostic value of interstitial inflammation in a two-center retrospective cohort study from China. They included 1,420 patients with IgAN (diagnosed by kidney biopsy between 2003 and 2013) with an average follow-up of 7 years. In a propensity matching sub-study, 181 patients with non-mild interstitial inflammation were compared to 181 patients with moderate to severe interstitial inflammation.

After full adjustments for covariates, a higher level of interstitial inflammation was associated with a faster decline of eGFR. The propensity matching sub-study gave similar results. Incorporating the interstitial inflammation severity into the IgAN-PT improved the capability of this tool to predict outcome. Overall, all the area under the curve analyses of the receiver operating characteristics showed only a modest increase in values from 0.81 to 0.83, but both the Net Reclassification Index and the Integrated Discrimination Index showed improvement when interstitial inflammation was added as a variable. Previously, interstitial inflammation was discarded by the Oxford-MEST-C development group as it was highly correlated with interstitial fibrosis. Perhaps the differences in the findings of this study could be explained by the retrospective nature of the study and the unique Chinese ancestry of the cohort. Nevertheless, this study raises important questions about the utility of adding interstitial inflammation to the list of important predictive factors identified in pathological analysis of kidney biopsies from subjects with IgAN.

Richard Glassock

Quoted Karger Article

Renal Interstitial Inflammation Predicts Nephropathy Progression in IgA Nephropathy: A Two-Center Cohort Study