**Core Concept**
Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by symmetrical, inflammatory polyarthritis, leading to joint damage and deformity. Key features of RA include joint inflammation, cartilage and bone destruction, and characteristic deformities.

**Why the Correct Answer is Right**
Heberden nodes are a type of bony growth that occurs on the distal interphalangeal joints (DIP), typically associated with osteoarthritis (OA). They are not a feature of rheumatoid arthritis, which primarily affects the proximal interphalangeal joints (PIP) and metacarpophalangeal joints (MCP). The formation of Heberden nodes in OA is due to the accumulation of calcium deposits on the surface of the bone, leading to bony outgrowths.

**Why Each Wrong Option is Incorrect**
**Option B:** Swan neck deformity is a characteristic feature of rheumatoid arthritis, resulting from flexion of the proximal interphalangeal joint (PIP) and hyperextension of the distal interphalangeal joint (DIP).

**Option C:** Ulnar deviation of fingers at the metacarpophalangeal joint is a common deformity seen in rheumatoid arthritis, due to the loss of ligamentous support and subsequent subluxation of the joints.

**Option D:** Symmetric reduction of joint space is a hallmark feature of rheumatoid arthritis, resulting from the destruction of cartilage and bone in the affected joints.

**Clinical Pearl / High-Yield Fact**
In rheumatoid arthritis, the pattern of joint involvement is symmetrical, with the same joints affected on both sides of the body. This is in contrast to osteoarthritis, which typically affects weight-bearing joints and exhibits asymmetrical involvement.

**✓ Correct Answer: A. Heberden nodes. Heberden nodes are not a feature of rheumatoid arthritis.**