Osteoarthritis vs rheumatoid arthritis: distinguishing features on exam and labs?

• A. OA: asymmetric, mechanical pain, osteophytes; RA: symmetric small-joint involvement; RA markers RF/anti-CCP; ESR/CRP elevated; erosions for RA, osteophytes for OA.
• B. OA: symmetric; RA asymmetric.
• C. RA markers present only in elderly.
• D. OA shows erosions.

Answer: (A)

Pattern of joint involvement and labs distinguishes OA from RA. Osteoarthritis tends to affect joints asymmetrically and presents with mechanical pain that worsens with use and improves with rest; radiographs typically show osteophytes and joint-space narrowing, with little to no true erosions. Rheumatoid arthritis usually involves small joints of the hands and feet in a symmetric pattern, with inflammatory-type pain and prolonged morning stiffness. Serology is often positive for RA-specific antibodies (rheumatoid factor and anti-CCP), and inflammatory markers like ESR or CRP are elevated during flare-ups. Imaging in RA shows erosions and periarticular osteopenia, whereas OA shows osteophytes rather than erosions. This combination—asymmetric OA features with osteophytes versus symmetric RA features with RA serology, elevated inflammatory markers, and erosions—best matches the correct answer.