[Rheumatoid arthritis and the kidney. Pinpointing an aspect of confusing contours]

In literature there are only a few papers about renal involvement in rheumatoid arthritis. The scarcity of reports is due to the difficulties of pinpointing this subject; in fact a bloody investigation like kidney biopsy is necessary to obtain an exact diagnosis. Moreover it is often clinically hard to distinguish renal injury provoked by rheumatoid arthritis from nephropathy caused by drugs, either non steroidal antiinflammatory drugs or disease modifying antirheumatic drugs. This topic is perhaps neglected because primary renal involvement in rheumatoid arthritis is not considered to influence the survival, with the exception of renal amyloidosis. Pathologic examination of kidney biopsy shows in order of frequency: mesangial nephritis, renal amyloidosis, membranous nephritis, focal proliferative nephritis, minimal nephritis, interstitial nephritis. Both immune complexes and antineutrophil cytoplasmic antibodies may play a pathogenetic role. The mesangial nephritis with IgA or IgM deposits is linked to high levels of rheumatoid factor of IgA or IgM class; it has been hypothesized that the ability of mesangium to remove circulating immune complexes provokes the mesangial damage. Moreover it has been observed that rheumatoid arthritis with renal involvement shows positivity for perinuclear antineutrophil cytoplasmic antibodies more frequently than rheumatoid arthritis without nephropathy. Also in the former cases the title of these autoantibodies is higher. The aim of this paper is to bring the terms of the problem into focus by the revision of the literature. Further and wider studies are necessary to obtain more available data.