Diagnostic Criteria of Osteoarthritis (OA) vs. Rheumatoid Arthritis (RA)

Osteoarthritis (OA) and Rheumatoid Arthritis (RA) are the two most common forms of arthritis, both causing joint pain and stiffness, but they have distinct causes, mechanisms, and diagnostic criteria. Understanding these differences is crucial for accurate diagnosis and appropriate treatment.

Osteoarthritis (OA) – “Wear and Tear” Arthritis

• Cause: OA is a degenerative joint disease resulting from the breakdown of cartilage, the protective tissue that cushions the ends of bones in a joint. This breakdown occurs due to mechanical stress, aging, injury, or overuse. It’s primarily a “mechanical” problem.
• Key Diagnostic Criteria/Features:
  • Onset: Gradual, insidious onset, often developing over many years.
  • Affected Joints: Typically affects weight-bearing joints (knees, hips, spine) and frequently used joints (hands, fingers at the DIP and PIP joints, base of the thumb). It tends to be asymmetrical (affecting one side more than the other, or isolated joints initially).
  • Morning Stiffness: Present, but usually short-lived (less than 30 minutes), and improves with movement.
  • Pain Pattern: Worsens with activity, movement, and weight-bearing, and improves with rest. Pain tends to be worse later in the day.
  • Swelling: May be present, but often mild, firm (due to bone spurs), and less inflammatory than RA.
  • Joint Deformity: May develop, characterized by bony enlargement (osteophytes or bone spurs), e.g., Heberden’s nodes (DIP joints) and Bouchard’s nodes (PIP joints) in the fingers.
  • Systemic Symptoms: Absent. OA is generally not associated with systemic symptoms like fever, fatigue, or weight loss.
  • Imaging (X-rays): Show characteristic changes like:
    • Joint space narrowing (due to cartilage loss).
    • Osteophytes (bone spurs).
    • Subchondral sclerosis (increased bone density beneath the cartilage).
    • Subchondral cysts.
  • Laboratory Tests: No specific blood tests for OA. Inflammatory markers like ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein) are typically normal or only mildly elevated, if at all.