Mesangial glomerulonephritis as an extra-articular manifestation of rheumatoid arthritis.

Mesangial glomerulonephritis (MesGN) is a frequent renal biopsy finding in patients with rheumatoid arthritis (RA) presenting with haematuria and/or proteinuria. The purpose of this study was to describe the mesangial immunofluorescence (IF) findings in 37 such RA patients, and to correlate the nature of the glomerular immunodeposits with clinical data, levels of serum immunoglobulins and the concentrations of serum rheumatoid factors (RFs). The serological findings in RA patients with MesGN were correlated with those of RA patients matched for age, sex and duration of RA, but without clinically evident renal disease. The most characteristic mesangial IF finding in 37 RA patients with MesGN was IgM observed in 29 specimens (78%). IgA (n = 16) and C3 (n = 15) deposits were also frequently found, whereas C1q (n = 3) and IgG (n = 2) deposits were only occasionally seen. Two main patterns of IF findings could be classified. (1) Granular IgM deposits as a sole or main finding (IgM GN; 25 specimens). The intensity of the mesangial IgM deposits did not correlate with the duration or severity of RA nor with the levels of serum immunoglobulins. However, a significant correlation with the intensity of mesangial IgM deposits and the levels of serum IgM class RF was observed. (2) Granular IgA deposits usually together with the complement component C3, i.e. IgA glomerulonephritis (IgA GN; nine specimens). The intensity of mesangial IgA deposits correlated significantly with the duration and severity of RA, and especially with serum IgA levels. Both RA patients with IgA GN or IgM GN were associated with a more frequent occurrence and higher titres of serum RFs when compared with the RA patients without nephropathy. The clinicopathological correlations and the association with RF support the concept that MesGN is related to the basic rheumatoid disease, and it should be regarded as an extra-articular manifestation of RA.