[Mesangiocapillary glomerulonephritis and rheumatoid arthritis. A case with diagnostic and therapeutic questions (author's transl)].

A 34 years old white male patient suffering from a seropositive "probable" rheumatoid arthritis developed a severe hypocomplementemic mesangiocapillary glomerulnophritis. Rheumatoid factor-Latextest and Waaler-Rose-Titers and IgM have been found highly elevated in the serum. The third component of complement (C3) was markedly depressed, while the fourth component (C4) was within the normal range. The rapid progression of both diseases forced us to start an immunosuppressive drug therapy using azathioprine and steroids, 18 months after the beginning of the treatment the patient is well, has only slight proteinuria, normal levels of complement and no joint pain. The possible connections between rheumatoid arthritis and mesangiocapillary glomerulonephritis in this case as well as the therapeutic approaches are discussed.