Amyloid casts within renal tubules: a singular finding in myelomatosis

This study was carried out in order to investigate a possible relationship between multiple myeloma and the occurrence of material exhibiting the properties of amyloid within renal tubules. Two groups of autopsied patients, with myelomatosis and benign monoclonal gammopathy were examined for the presence of amyloid deposits in renal and extra-renal sites. Urines were analysed for the presence and amount of Bence Jones protein and the pattern of the associated proteinuria was characterized. Renal tubular casts exhibiting the histochemical characteristics of immuno-amyloid were found exclusively in myeloma patients with Bence Jones proteinuria but without the renal lesions classically described as "myeloma kidney". This finding was independent of the occurrence of immuno-amyloid deposits in other renal and extra-renal sites, suggesting involvement of local factors in the pathogenesis of amyloid formation and deposition within renal tubular lumina. The results of present study suggest the conclusion that the presence of amyloid intratubular casts is to be regarded as a peculiar finding in myelomatosis.