PURPOSE: To present a case of fibrillary glomerulonephritis (FGN) with mixed connective tissue disease (MCTD) controlled with rituximab

SUMMARY: FGN is a rare glomerular disease found in 0.5%-1% of native kidney biopsy series. It is usually associated with underlying malignancy, hepatitis C infection or certain autoimmune diseases mostly found in Graves’ disease, systemic lupus, Crohn’s disease, and idiopathic thrombocytopenia purpura. In general, renal involvement in MCTD is infrequent at early stage, but is often observed and complicates the clinical course where the membranous and mesangial proliferative glomerulonephritis have been reported.

We report an 80 year-old female with history of MCTD with scleroderma, interstitial lung disease, hypertrophic cardiomyopathy, as well as prior diagnosis of rheumatoid arthritis and lupus at her 50s, who has developed chronic kidney disease due to FGN. Patient initially presented in nephrology clinic with hypertension, renal insufficiency and sterile pyuria. Occasional mild proteinuria and cellular casts were observed and thought to be tubulointerstitial nephropathy. Renal biopsy later revealed fibrillary and immune complex mediated glomerulonephritis. Extensive fibrillary deposits by electron microscopy warrant a diagnosis of FGN. Rituximab was initiated afterward since 2016 for empirical FGN treatment although the data are limited and have inconsistent outcomes. Patient also has been on long-term Azathioprine for MCTD and lisinopril for Raynaud phenomenon. Her kidney function has remained stable at her baseline range of 1.1-1.5 since 2006. Urinalysis stays grossly negative except occasionally trace protein and sterile pyuria. She is currently following up with nephrology clinic every 6 months.

CONCLUSION: To the best of our knowledge, FGN with MCTD is rarely observed and FGN often entails poor prognosis with fast progression to end-stage kidney disease (ESKD). Here, we report a case of well-controlled FGN by rituximab with MCTD. It would also be prudent for physicians to keep FGN under one of differential diagnosis for renal involvement in MCTD.