## **Core Concept**
The question tests knowledge of joint involvement patterns in rheumatological conditions, particularly focusing on the distribution of joint involvement which is crucial for differential diagnosis.

## **Why the Correct Answer is Right**
The correct answer, **Psoriatic Arthritis (PsA)**, is suggested by the specific pattern of joint involvement described: Proximal Interphalangeal (PIP), Distal Interphalangeal (DIP), and Metacarpophalangeal (MCP) joints are involved, while the wrist and Carpometacarpal (CMC) joints are spared. PsA is known for its asymmetric joint involvement and can affect any joint, but it commonly involves the DIP joints, which is less typical for Rheumatoid Arthritis (RA). The involvement of DIP joints along with PIP and MCP joints and the sparing of wrist and CMC joints is characteristic.

## **Why Each Wrong Option is Incorrect**
- **Option A (Rheumatoid Arthritis):** Typically involves MCP and PIP joints symmetrically and often includes the wrist and CMC joints, which are spared in this case.
- **Option B (Osteoarthritis):** Usually involves DIP and PIP joints but doesn't commonly involve MCP joints to this extent and often involves the CMC joints.
- **Option D (Ankylosing Spondylitis):** Primarily affects the axial skeleton (spine and sacroiliac joints) and sometimes large peripheral joints, not typically the small joints of the hands in this pattern.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **Psoriatic Arthritis** can present with a variety of skin manifestations, including psoriasis, and the joint involvement can precede skin symptoms. The pattern of joint involvement, including the DIP joints, should prompt consideration of PsA.

## **Correct Answer:** . Psoriatic Arthritis