Membranous nephropathy caused by rheumatoid arthritis.

Membranous nephropathy (MN) caused by disease-modifying antirheumatic drugs is relatively common in patients with rheumatoid arthritis (RA). However, MN rarely occurs due to RA itself. We describe a 61-year-old woman with RA who showed nephrotic syndrome. She was admitted because of systemic edema and severe arthritis. She had a long history of RA successfully treated with methotrexate (MTX), but discontinued all treatments 4 years before hospitalization. She had never been treated with bucillamine or gold. Laboratory test results were positive for anti-cyclic citrullinated peptide antibody and negative for anti-nuclear antibody. Renal pathologic findings were compatible with MN. Immunofluorescence microscopy showed IgG, IgA, κ, λ, and C3 along the glomerular capillary wall, whereas deposition of IgM or C1q was not detected. In terms of the IgG subclasses, only IgG2 findings were positive. Results for glomerular antigen and serum antibody for M-type phospholipase A2 receptor and thrombospondin type 1 domain-containing 7A were negative. HLA type did not include the HLA-DQA1 gene that is a concern in primary MN (PMN). She responded to intensive immunosuppressive therapy consisting of prednisolone, tacrolimus, and MTX with a parallel reduction of proteinuria. Based on assessments for differentiating PMN from secondary MN (SMN), the diagnosis of the present case was incompatible with PMN. Taken together, we consider that SMN in the present case was due to RA itself rather than drug-induced MN.