Rheumatoid Arthritis (RA) primarily affects which part of the body?

Rheumatoid Arthritis (RA) is primarily characterized by inflammation of the joints. It is an autoimmune disorder that leads to a chronic inflammatory response, affecting the synovial lining of the joints. This results in pain, swelling, and stiffness in the affected areas, which can significantly impair mobility and functionality. Over time, persistent inflammation can lead to joint damage and deformities.

The primary impact of RA on the joints distinguishes it from other conditions that may affect muscles, nerves, or skin. While RA can indeed have systemic effects that might involve other areas of the body—such as fatigue, fever, and malaise, which are not specific to the joints—the hallmark features of the disease are localized to the joints themselves. This strong association with joint inflammation and damage is why the correct answer is focused on the joints.