The Interplay Between Rheumatoid Arthritis and Chronic Kidney Disease: From Mechanisms to Treatment.

Chronic kidney disease (CKD) is a frequent and clinically significant comorbidity in patients with rheumatoid arthritis (RA), with a reported prevalence ranging from 20% to 50% depending on the cohort and definition applied. The high burden of CKD in RA reflects the complex interplay between traditional risk factors (aging, hypertension, diabetes, and dyslipidemia) and RA-specific factors such as persistent systemic inflammation, immune complex deposition, and long-term exposure to nephrotoxic agents, including older DMARDs (gold, D-penicillamine) and calcineurin inhibitors. Histopathologically, RA-associated kidney involvement encompasses a broad spectrum of conditions, including mesangial proliferative glomerulonephritis, membranous nephropathy, AA amyloidosis, and drug-induced interstitial nephritis. Recent advances in RA therapy, particularly the widespread use of biologic DMARDs, have markedly reduced the incidence of AA amyloidosis and may exert indirect renoprotective effects through stringent inflammation control. However, targeted synthetic DMARDs such as Janus kinase (JAK) inhibitors require careful dose adjustment in CKD and heightened infection vigilance. CKD in RA is a strong predictor of cardiovascular events, serious infections, and all-cause mortality. Importantly, recent data indicate that even low-grade albuminuria below the traditional microalbuminuria threshold is associated with excess mortality in RA. Early detection through routine monitoring of eGFR and urinary albumin-to-creatinine ratio (uACR), combined with individualized pharmacologic adjustment and close collaboration with nephrologists, is essential for optimizing long-term outcomes. This review provides an updated synthesis of the epidemiology, pathophysiological mechanisms, therapeutic strategies, and prognostic implications of CKD in RA, with a particular focus on both Japanese and international evidence.