A 42-year-old woman presents with symmetric polyarthritis of the hands and wrists for 8 weeks, morning stiffness lasting 2 hours, and progressive functional impairment. Clinical examination reveals soft tissue swelling and warmth over the PIP and MCP joints bilaterally. Which investigation is most appropriate to confirm the diagnosis of rheumatoid arthritis and assess disease activity?

Explanation

## Diagnostic Approach to Rheumatoid Arthritis **Key Point:** Anti-CCP (anti-cyclic citrullinated peptide) antibodies and rheumatoid factor are the gold-standard serological tests for RA diagnosis and are part of the 2010 ACR/EULAR classification criteria. ### Why Anti-CCP and RF Together? **High-Yield:** Anti-CCP antibodies are: - More specific (95–98%) than RF for RA - Present early in disease (preclinical phase) - Predictive of erosive disease and poor prognosis - Positive in ~70% of RA patients (including seronegative cases where RF is negative) Rheumatoid factor adds: - Sensitivity (~80% in established RA) - Prognostic value when combined with anti-CCP - Confirmation of diagnosis ### Classification Criteria Context The 2010 ACR/EULAR criteria require: 1. Joint involvement score (symmetric small joints) 2. Serology score (RF and/or anti-CCP) 3. Acute phase reactants (CRP/ESR) 4. Duration ≥6 weeks This patient meets duration and clinical criteria; serology is the next confirmatory step. **Clinical Pearl:** A patient who is both RF+ and anti-CCP+ has the highest risk of severe, erosive disease and warrants aggressive early DMARD therapy. ### Investigation Comparison Table | Investigation | Sensitivity | Specificity | Timing | Prognostic Value | |---|---|---|---|---| | Anti-CCP | 70% | 95–98% | Early disease | High (erosions) | | Rheumatoid Factor | 80% | 85% | Established disease | Moderate | | RF + Anti-CCP combined | 85% | 98% | Diagnostic | Highest | | ESR/CRP | Variable | Low | Activity marker | Activity only | | X-ray | — | — | Late changes | Damage assessment | **Mnemonic:** **SEROLOGY FIRST** — Serology (RF + anti-CCP) → Exclude other causes → Radiography (if diagnosis unclear) → Observe response to therapy → Lifestyle/DMARD initiation → Ongoing monitoring → Graded progression assessment.