**Core Concept**
Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by symmetric polyarthritis, predominantly affecting the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints. In contrast, distal interphalangeal (DIP) joints are typically spared in RA, but frequently involved in other arthritic conditions.

**Why the Correct Answer is Right**
Rheumatoid arthritis primarily targets the synovial tissues of the PIP and MCP joints, with the DIP joints being relatively resistant to the disease process. This is due to the unique anatomy of the DIP joint, which has a thicker cartilage layer and a more robust joint capsule compared to the PIP and MCP joints. As a result, DIP joints are less prone to synovial inflammation and cartilage destruction in RA.

**Why Each Wrong Option is Incorrect**
**Option A:** Psoriatic arthritis often involves the DIP joints, particularly in the context of "pencil-in-cup" deformities, where the DIP joint becomes severely damaged and deformed.
**Option C:** Reactive arthritis, a form of spondyloarthritis, can also affect the DIP joints, among other joints, in response to an infection, usually in the gastrointestinal or genitourinary tract.
**Option D:** Osteoarthritis (OA) commonly affects the DIP joints, leading to characteristic Heberden's nodes, which are bony enlargements of the DIP joints.

**Clinical Pearl / High-Yield Fact**
When evaluating patients with arthritic conditions, remember that the involvement of DIP joints can help differentiate between RA and other forms of arthritis, such as OA or psoriatic arthritis.

✓ Correct Answer: B. Rheumatoid arthritis