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Why does rheumatoid arthritis often affect the same joints on both sides of the body?
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Rheumatoid arthritis is a chronic autoimmune disease in which the immune system mistakenly attacks the body's own tissues, specifically the synovial membranes that line the joints.12
While the exact trigger for this systemic response remains unknown, the condition is characterized by widespread inflammation throughout the body's connective tissues. Because the immune system circulates throughout the body, the resulting inflammatory process is not localized to a single area. Instead, it systematically targets the same types of tissues in multiple locations, which is why the disease typically manifests symmetrically, affecting joints on both sides of the body—such as both hands, both knees, or both ankles—simultaneously.12