What are the steps to diagnose Rheumatoid Arthritis (RA)?

Diagnosing Rheumatoid Arthritis (RA)

The diagnosis of rheumatoid arthritis requires at least one joint with definite clinical synovitis (swelling) not better explained by another disease, and a score of ≥6/10 points on the 2010 ACR/EULAR classification criteria which evaluates joint involvement, serology, acute phase reactants, and symptom duration. 1, 2

Initial Clinical Assessment

• Evaluate for symmetric involvement of small joints, particularly metacarpophalangeal joints, proximal interphalangeal joints, wrists, and metatarsophalangeal joints, which is characteristic of RA 1
• Note that large joints (shoulders, elbows, hips, knees, ankles) may also be affected, while distal interphalangeal joints, first carpometacarpal joints, and first metatarsophalangeal joints are typically spared 1
• Morning stiffness in and around joints lasting at least 1 hour is a typical sign of RA 3
• Clinical examination is the method of choice for detecting arthritis, which may be confirmed by ultrasonography 4

Laboratory Testing

• Perform the following essential laboratory tests 4:

  • Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
  • Rheumatoid factor (RF) and anti-citrullinated protein antibody (ACPA)
  • Complete blood count with differential
  • Liver function tests and renal function tests

• Interpret serological findings according to the 2010 ACR/EULAR criteria 1, 2:

  • Negative RF and negative ACPA = 0 points
  • Low positive RF or low positive ACPA = 2 points
  • High positive RF or high positive ACPA = 3 points

• Note that while RF has moderate sensitivity (60-80%) for RA, ACPA has higher specificity (90%) 4, 5

Imaging Studies

• Perform X-rays of affected joints at baseline 4
• X-rays of hands, wrists, and feet should be obtained as the presence of erosions is predictive for the development of RA and persistence of disease 4
• Consider ultrasound or MRI when clinical examination is inconclusive, as these modalities are more sensitive in detecting early synovitis 4, 1
• Radiographic features in early disease include soft tissue swelling and mild juxtaarticular osteopenia 3

2010 ACR/EULAR Classification Criteria Scoring

Apply the following scoring system (≥6/10 points needed for definite RA diagnosis) 1, 2:

1. Joint involvement (0-5 points):

   • 1 large joint = 0 points
   • 2-10 large joints = 1 point
   • 1-3 small joints = 2 points
   • 4-10 small joints = 3 points

   • 10 joints (at least 1 small joint) = 5 points

2. Serology (0-3 points):

   • Negative RF and negative ACPA = 0 points
   • Low positive RF or ACPA = 2 points
   • High positive RF or ACPA = 3 points

3. Acute phase reactants (0-1 points):

   • Normal CRP and ESR = 0 points
   • Abnormal CRP or ESR = 1 point

4. Duration of symptoms (0-1 points):

   • <6 weeks = 0 points
   • ≥6 weeks = 1 point

Disease Activity Assessment

• Use composite measures to quantitatively assess disease activity 4, 1:

  • Disease Activity Score using 28 joint counts (DAS28)
  • Simplified Disease Activity Index (SDAI)
  • Clinical Disease Activity Index (CDAI)

• These measures should be performed at baseline and repeated at 1-3 month intervals until treatment targets are reached 4

Common Pitfalls and Caveats

• A negative RF or ACPA does not exclude RA diagnosis, as these can be negative in early disease 5
• Consider differential diagnoses including other inflammatory arthritides (psoriatic arthritis, ankylosing spondylitis), osteoarthritis, crystal arthropathies, and viral or reactive arthritis 5
• If clinical suspicion for RA remains high despite negative serology, additional testing and close monitoring are warranted 5
• Early diagnosis is critical as prompt treatment with disease-modifying antirheumatic drugs (DMARDs) is associated with better outcomes 6, 7

By following this diagnostic approach, clinicians can accurately identify RA and initiate appropriate treatment to prevent joint destruction and disability.