Unlike SLE and lupus nephritis, other rheumatologic diseases have not been well studied in regards to their association with kidney disease. In a recent article published by AJKD, Hickson et al discovered that patients with rheumatoid arthritis (RA) were more likely to experience GFR loss over time. They postulated that cardiovascular disease-related factors led to this decline.
Is it only the cardiovascular risk that leads to loss of kidney function? RA has been associated with chronic inflammation, and AA amyloidosis is a common finding in these patients. In addition, biopsies of patients with RA have found many types of glomerular injury including minimal change disease, proliferative GN, and IgA nephropathy, suggesting an auto-immune phenotype. In a study of 110 patients with RA who underwent kidney biopsy for evaluation of kidney disease presumably related to RA or its therapy, a mesangio-proliferative glomerulonephritis was the most common finding. In addition, anti TNF-alpha treatment has been associated with kidney diseases such as ANCA vasculitis. Finally, rheumatoid vasculitis is an uncommon presentation in the kidney. Despite heavy NSAID use by patients in this study, the authors didn’t find that specific association. In their study, only 2 factors, BMI <20kg/m2 and NSAID use were associated with lower risk of developing eGFR <60 mL/min/1.73m2, but this did not extend to eGFR <45 mL/min/1.73m2. So what were the primary risk factors associated with eGFR <45 mL/min/1.73m2?: ESR in the first year, severe extra-articular findings, and steroid use.
This is not a new association. In the Methotrexate And Renal Insufficiency (MATRIX) study of 129 patients, 20% of patients had an estimated glomerular filtration rate (eGFR) of 60 to 89 mL/min/1.73m2, and 15% had an eGFR of 30 to 59 mL/min/1.73m2.
Should nephrologists and rheumatologists perform more kidney biopsies in RA patients? Perhaps we are missing an opportunity to treat an autoimmune disease where good therpy exists. Should we be checking their kidney function more often given the above risk factors? These are tough questions that we may not have answers to, but this study gives us a preliminary look at future prospective studies that might provide more answers.
eAJKD Blog Editor