Light chain crystalline podocytopathy caused by electron-lucent crystals - a diagnostic challenge: a case report.

We report here a challenging diagnosis of light chain crystalline podocytopathy in a patient with sub-nephrotic proteinuria, microscopic hematuria, glucosuria and elevated free kappa light chains but without any initial clinical evidence of frank multiple myeloma. We also discuss the diagnostic challenges of this case which include rather unique and seemingly innocuous light microscopic morphology of the glomeruli and the critical roles of paraffin immunofluorescence and need for electron microscopy to confirm the diagnosis. The kappa restriction of the crystals within the podocytes was confirmed only by paraffin immunofluorescence (it went undetected by routine immunofluorescence) and electron microscopy of the glomeruli showed the podocytopathy to be caused by electron-lucent crystals which is a rare variant of light chain crystals, with electron-dense crystals being the predominant variant of light chain crystals.