Podocyte Infolding Glomerulopathy (PIG) in a Patient With Undifferentiated Connective Tissue Disease: A Case Report

Podocyte infolding glomerulopathy (PIG) is a recently described pathologic entity characterized by diffuse podocyte infolding into the glomerular basement membrane (GBM) associated with ultrastructurally demonstrable microspherular aggregates. The clinical features, significance, and pathogenesis of this condition are still not well delineated because only a few cases have been documented to date, all from Japan. We report a case of PIG associated with undifferentiated connective tissue disease in an Indian woman who presented with nephrotic syndrome while undergoing treatment for an autoimmune disorder. Ultrastructural analysis of the kidney biopsy specimen revealed unusual subepithelial aggregates of microspherules admixed with few microtubules alongside extensive infolding of podocyte foot processes into the underlying GBMs. Characteristic clustering of these microparticles near the invaginated tips of podocyte foot processes in the GBM was observed on transmission electron microscopy. The patient's clinical condition responded favorably to immunosuppressive therapy. The clinical, light microscopic, and diagnostic electron microscopic features of this condition are highlighted in this report in an attempt to contribute some insights into the possible pathogenetic mechanisms of this obscure entity.