**Question:** A 35 year old male patient develops involvement of proximal and distal interphalangeal joints and 1st carpo-metacarpal joints with sparing of wrist and metacarpophalangeal joint. The Diagnosis is:

A. Rheumatoid Arthritis
B. Psoriatic Arthritis
C. Ankylosing Spondylitis
D. Gout

**Correct Answer:** **C. Ankylosing Spondylitis**

**Core Concept:** Ankylosing Spondylitis is a type of inflammatory arthritis that primarily affects the spine and sacroiliac joints. It is a subtype of Spondyloarthritis, which also includes conditions like Reactive Arthritis and Psoriatic Arthritis. The disease is characterized by symmetrical involvement of the axial skeleton, particularly affecting the spine and sacroiliac joints.

**Why the Correct Answer is Right:** Ankylosing Spondylitis presents with symmetrical involvement of the axial skeleton, particularly affecting the spine and sacroiliac joints. The patient's symptoms and radiological findings in this case (involvement of proximal and distal interphalangeal joints and first carpo-metacarpal joints with sparing of wrist and metacarpophalangeal joint) align with the clinical presentation of Ankylosing Spondylitis.

**Why Each Wrong Option is Incorrect:**

A. Rheumatoid Arthritis: It typically affects small joints and is symmetrical, not involving the first carpo-metacarpal joints and sparing the wrist and metacarpophalangeal joints as seen in Ankylosing Spondylitis.

B. Psoriatic Arthritis: Although it may involve the axial skeleton, it does not typically present with the described pattern of involvement in this question.

D. Gout: Gout typically presents with acute attacks of painful, swollen, and red joints, and does not involve the described pattern of involvement in this question.

**Clinical Pearl:** Ankylosing Spondylitis often presents with back pain, stiffness, and morning stiffness, and may be associated with HLA-B27 positivity in genetic screening. Understanding the clinical presentation, radiological findings, and genetic associations is crucial in differentiating Ankylosing Spondylitis from other arthritic conditions.