**Question:** In rheumatoid arthritis the characteristic joint involvement is:

A. Multiple joints involvement
B. Involvement of small joints only
C. Involvement of large joints only
D. Unilateral joint involvement

**Core Concept:** Rheumatoid arthritis (RA) is an autoimmune disorder where the immune system attacks the synovial membrane, leading to inflammation and joint destruction. The characteristic joint involvement in RA is the result of immune system dysfunction and subsequent joint damage.

**Why the Correct Answer is Right:** In rheumatoid arthritis, the immune system becomes hyperactive and attacks the synovial membrane in multiple joints, which leads to inflammation and joint destruction. This results in a pattern of symmetrical joint involvement, affecting both sides of the body simultaneously. The correct answer, "Multiple joints involvement," accurately describes the characteristic pattern of joint involvement in RA.

**Why Each Wrong Option is Incorrect:**

A. Multiple joints involvement: While RA can indeed affect multiple joints, the correct answer already covers this aspect.
B. Involvement of small joints only: RA can affect any joint size, not just small ones. The correct answer addresses joint size but is not specific enough.
C. Involvement of large joints only: RA does not exclusively affect large joints. The correct answer covers the joint size but not symmetrical joint involvement.
D. Unilateral joint involvement: RA demonstrates a symmetrical joint involvement pattern, not unilateral joint involvement.

**Clinical Pearl:** RA is a systemic disease with various extra-articular manifestations like rheumatoid nodules, lung involvement (pulmonary fibrosis), and vasculitis. It is essential for students to understand the joint involvement pattern in RA to recognize this disease and differentiate it from other conditions with similar joint involvement patterns, such as psoriatic arthritis and ankylosing spondylitis.

**Correct Answer:** Multiple joints involvement