In rheumatoid arthritis, what is the primary tissue targeted by the disease?

• A. Tendon sheath
• B. Synovium
• C. Bone
• D. Cartilage

Answer: (B)

Rheumatoid arthritis primarily targets the synovial membrane, or synovium. The disease starts as an autoimmune attack on the lining of the joint, leading to chronic synovitis with immune cell infiltration and inflammatory cytokine release. This inflammatory process causes synovial cells to proliferate and form pannus, a destructive tissue that gradually invades and erodes cartilage and underlying bone. So while bone and cartilage destruction occur as a consequence of the ongoing synovitis, the initial and main tissue affected is the synovium. Tendon sheaths and other structures can be involved later, but they are not the primary target.