Mesangial glomerulopathy and IgM rheumatoid factor in rheumatoid arthritis.

Hematuria and proteinuria in rheumatoid arthritis (RA) are commonly associated with drug therapy but occur independently of drugs, amyloid or urologic disorders. The latter occurrences suggest a primary renal lesion associated with RA. Review of reported renal biopsies identifies mesangial glomerulopathy as a common finding in RA patients without associated drug therapy and that it is frequently associated with hematuria in nonrheumatoid patients. Moreover, immunoglobulins have been shown to concentrate in the mesangium in experimental animals, suggesting that a functional response by the kidney mesangium to remove IgM rheumatoid factor (RF)-IgG complexes could lead to this mesangial lesion. We describe 3 patients with RA who had a mesangiopathy characterized by increased quantities of mesangial matrix and deposition of IgM without other lesions. Together, these observations suggest that: (1) mesangial glomerulopathy is common in RA; (2) removal of circulating RF-IgG complexes is a function of the mesangium and might produce this renal lesion; (3) mesangial glomerulopathy may be responsible for much of the hematuria observed in RA patients and, in many cases, may not be drug related and thus may not require discontinuing beneficial therapy.