Expert Discussion on Immune Complex-Mediated Membranoproliferative Glomerulonephritis: Challenges and Considerations.

Immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) is a rare pattern of kidney injury and a progressive nephropathy characterized by the glomerular deposition of immune complexes and complement proteins. The IC-MPGN pattern of injury exhibits a membranoproliferative glomerulonephritis appearance by light microscopy and occurs secondary to various conditions or, more rarely, idiopathically, when no underlying etiology can be determined. Kidney biopsy is the only method for identifying IC-MPGN, distinguishing between IC-MPGN and complement 3 glomerulopathy (C3G), and for providing critical pathologic insights that guide further clinical evaluation for underlying etiologies and inform patient management. Given the progressive nature of IC-MPGN, it is crucial to identify patients early and to define the underlying pathophysiology for timely and appropriate treatment. However, several challenges remain in the accurate interpretation of kidney biopsy specimens and the effective treatment of idiopathic disease. In this commentary, two nephrologists and a nephropathologist review best practices in the clinical and histopathologic evaluation of IC-MPGN and discuss the central role of kidney biopsy in the differentiation of IC-MPGN and C3G. The challenges and considerations discussed are explored through an illustrative case of idiopathic disease, drawn from the authors' clinical experiences. Finally, remaining unmet needs are highlighted, and future perspectives on targeted treatments under investigation for patients with idiopathic IC-MPGN are provided.