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Diverse forms of kidney pathology are associated with plasma cell dyscrasias, including Multiple Myeloma (MM). Some pathologic lesions identified are cast nephropathy (LCCN) and light chain proximal tubulopathy (LCPT). There have been rarely reported instances of coincidental LCPT and LCCN. There are crystalline forms of these diseases. We report here the co-occurrence of these monoclonal crystalline forms of acute kidney injury in a 63-year-old man with suspected monoclonal gammopathy.
We report a 63-year-old man with a history of macrocytic anemia (HB 8.79), (platelets 245.700), creatinine 2.07, ureic nitrogen (BUN) 37.2, serum immunofixation with kappa monoclonal component (279.9) . Suspected monoclonal gammopathy.
The renal biopsy showed 10 glomeruli, 3 with global sclerosis. At the tubular level, the presence of crystalline and globular inclisions was observed at the proximal tubules with marked degenerative changes in the tubular epithelium, loss of the brush border and fragmentation (Fig 1-2). Presence of hyaline casts with the presence of celular reaction, which react very weakly with PAS stain (Fig 3), are negative with methenamine silver stains and show metachromasia with Masson´s trichrome stains (Fig 4). We also observed tubular atrophy and interstitial fibrosis of 25% of the simple examined. Inmunohistochemistry studies in paraffin show a predominance of kappa light chains over lambda light chains in proximal tubules and cast suggesting monotype (Fig 5-6). In the electron microscopy study, tubular vacuolization and loss of the brush border and accumulations of lysosomes and inclusions that look like needles and crystals are observed, as well as electron dense cast (Fig 7-8). Diagnosis is made of a crystalline light chain nephropathy with coincidental cast nephropathy and proximal tubulopathy.
These findings are indicative of acute tubular damage secondary to excess filtration of kappa light chains. Two varieties of tubulopathy associated with the presence of light chain are observed: the crystalline form as in our case, in which numerous crystals predominantly kappa light chains of different sizes are found in the proximal tubule within lysosomes or freely in the cytoplasm. The second is a Non-crystalline forms in which the lysosomal inclusions usually Lambda chain, distends or occupy the cytoplasm of the proximal tubule epithelium. Our patient underwent a bone marrow biopsy, shows an infiltration in 90% of the specimen by pathological plasma cells with kappa light chain restriction. The patient is currently undergoing a second cycle of chemotheraphy (Dara-VTD protocol), presenting improvement in kidney function.