New Onset Nephrotic - Range Proteinuria in a Patient with Chronic Kidney Disease - Not Always What it Seems

Light chain deposition disease (LCDD) is a rare condition that is characterized by the deposition of monoclonal immunoglobulin light chains in glomerular and tubular basement membranes. We report the case of a 72-year-old male with long-standing and stable chronic kidney disease (CKD) presumably due to hypertension and lithiasis who presented with new-onset nephrotic range proteinuria, anemia and rapidly worsening renal function that eventually led to end-stage renal disease (ESRD) requiring dialysis. Radiologic and laboratory workup found enlarged kidneys in the ultrasound and increased kappa/ lambda ratio (KLR) suggestive of a plasma cell dyscrasia. The patient underwent bone marrow biopsy, confirming the diagnosis of kappa light chains multiple myeloma (MM). Since exclusion of amyloidosis was essential for determining therapeutic strategies, a kidney biopsy was performed, showing deposition of Periodic acid-Schiff (PAS) positive and silver-negative material in the glomeruli, tubular basement membrane, vessels and interstitium and kappa light chain restriction in the immunofluorescence staining. A diagnosis of kappa LCDD secondary to MM was made, and the patient received a Bortezomib-based regimen directed to the plasma cell disorder.