This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Arthritis, Subject name: Orthopaedics
In which of the following condition, proximal interphalangeal joint is involved and distal interphalangeal joint is spared? 
Select and explain. 
A. Osteoarthritis, B. Psoriatic arthritis, C. Rheumatoid arthritis, D. Ankylosing spondylitis
C: Rheumatoid arthritis
Answer: C: Rheumatoid arthritis 
Explanation: Rheumatoid Arthritis* Overview# Systemic autoimmune inflammatory disease that primarily affects the hand and wrist.# Arthritis of hand joints lasting longer than 6 weeks is one of seven diagnostic criteria used by American College of Rheumatology.* In contrast to osteoarthritis, the DIP joints are usually soared in RA OARAPSORIATICJts involvedPIP, DIP & 1st CMC jtPIP, MCP, WristDIP, PIP, Any jointJts sparedMCP, Wrist & Ankle (as primary)DIP