Introduction: It is increasingly becoming accepted that inflammation may play an important role in the pathogenesis of Alzheimer's disease (AD), as several immune-related genes have been associated with AD. Among these is tumor necrosis factor (TNF)-α, a proinflammatory cytokine known to play an important role in autoimmune disorders, including rheumatoid arthritis (RA). Although AD and RA appear to involve similar pathological mechanisms through the production of TNF-α, the relationship between AD and RA remains unknown.
Objective: To determine the relative risk of AD among RA patients and non-RA patients, and whether anti-TNF therapy for RA was associated with a lower risk of AD in RA patients.
Methods: We performed a nested case-control study of more than 8.5 million commercially insured adults (aged ≥18 years) in all 50 US states, Puerto Rico, and US Virgin Islands in the Verisk Health claims database. We derived a sub-cohort of subjects with a diagnosis of RA (controls), or RA and AD (cases), matching cases and controls based on age, sex, exposure assessment period, and methotrexate treatment. We also assessed relative risk of AD following exposure to standard RA therapies, including anti-TNF agents (infliximab, adalimumab, etanercept), methotrexate, prednisone, sulfasalazine, and rituximab. Odds ratios were adjusted for comorbidities, including coronary artery disease, diabetes mellitus, and peripheral vascular disease.
Results: AD was more prevalent (p < 0.0001) among RA patients (0.79 %) than among those without RA (0.11 %). Chronic conditions such as coronary artery disease (odds ratio [OR] 1.48; 95 % confidence interval [CI] 1.04-2.05; p = 0.03), diabetes (OR 1.86; 95 % CI 1.32-2.62; p = 0.0004), and peripheral vascular disease (OR 1.61; 95 % CI 1.06-2.43; p = 0.02) significantly increased the relative risk of AD among RA patients. Exposure to anti-TNF agents as a class, but not other immunosuppressive drugs studied, was associated with lowered risk of AD among RA patients (unadjusted OR 0.44; 95 % CI 0.22-0.87; p = 0.02; adjusted OR 0.45; 95 % CI 0.23-0.90; p = 0.02). Sub-group analysis demonstrated that of the three anti-TNF agents studied, only etanercept (unadjusted OR, 0.33; 95 % CI 0.08-0.94; p = 0.03; adjusted OR 0.30; 95 % CI 0.08-0.89; p = 0.02) was associated with a decreased risk of AD in RA patients.
Conclusion: There is an increased risk of AD in the studied RA population. The relative risk of AD among RA subjects was lowered in those exposed to etanercept. Anti-TNF therapy with etanercept shows promise as a potential treatment for AD.