[The kidney in multiple myeloma. The physiopathological and clinical aspects]

The renal concern in a multiple myeloma (MM) case has a frequency of 50% and causes a worsening of the disease with a survival average of about 12 months. The monoclonal light free chains (CLL) produced in excess by the plasmacytes are present in the urine as proteinuria of Bence Jones (PBJ) in 60-70% of patients affected by MM. They represent the major pathogenetic factor of the nephropathy in course of MM as they can deposit in shape of intratubular "casts" in the myeloma casts nephropathy (MCN). In some worse cases, dehydration or hypercalcaemia can cause an irreversible acute renal insufficiency (RI). It is therefore important in a patient affected with MM with PBJ to prevent, locate and opportunely treat these situations which worsen the nephropathy. Beside the tubular cast nephropathy, the CLL "accumulate" in the kidney even though with a lower frequency compared to MCN, in the light chains deposition disease (LCDD) and in the amyloidosis AL (AL). LCDD is characterized by a deposit of nodular amorphous materials PAS positive in the glomerulus and sometimes even in the tubulus. It usually presents itself as a chronic RI and a proteinuria causing nephrotic syndrome (NS). This quickly evolves into uraemia and its evolution can be lessened by the MM treatment. AL in course of MM also reveals with a chronic RI and NS. CLLs deposit in the typical fibrillar structure, on the vessel walls, in the glomerulus, in the mesangium and can be marked out with the Congo red colouring and the subsequent green birefringence through microscope with polarized light. Prognosis of AL is extremely severe and no benefit is given by the treatment of the hematological illness. It is therefore absolutely necessary to study the renal histology through biopsy when MM is grade B, that is, with serumal creatinine above 2 mg/dl as: MCN imposes the MM treatment programme in order to reduce the tubular excess of PBJ and to attempt to make RI reversible; MCN with tubular atrophy and interstitial fibrosis results in an unfavourable prognosis as it expresses a nephropathic irreversibility due to the loss nephrons. It will therefore necessary to start on a renal substitutional treatment programme. Renal damage in course of MM is not always tubular, rather an unexpected glomerular damage of LCDD or amyloidosis AL type can be found.(ABSTRACT TRUNCATED AT 400 WORDS)