What is the appropriate evaluation and management for swelling of the right metacarpophalangeal joint?

Evaluation and Management of Right Knuckle Swelling

Immediately perform arthrocentesis to exclude septic arthritis before any other intervention, as infectious arthritis is the most critical diagnosis that cannot be missed in an acutely swollen joint. 1, 2, 3

Immediate Diagnostic Priorities

Rule Out Septic Arthritis First

• Joint aspiration must be performed urgently for cell count with differential, Gram stain, culture, and crystal analysis before administering corticosteroids or antibiotics, as septic arthritis requires immediate treatment to prevent irreversible joint destruction. 1, 4, 2
• Synovial fluid analysis with white blood cell count >50,000 cells/μL with neutrophil predominance strongly suggests bacterial infection, though lower counts do not exclude sepsis. 1
• A negative culture does not exclude septic arthritis, especially if antibiotics were already started. 1

Clinical Examination Details

• Assess for soft tissue swelling versus bony enlargement—inflammatory arthritis produces soft, boggy joint swelling from synovitis, while osteoarthritis causes hard, bony enlargement from osteophytes. 5
• Perform the "squeeze test" by applying lateral compression across the metacarpophalangeal joints; pain indicates inflammatory synovitis. 5, 6
• Document morning stiffness duration—stiffness lasting >30 minutes strongly suggests inflammatory arthritis (rheumatoid arthritis, psoriatic arthritis) rather than mechanical causes. 5, 7, 8
• Check for symmetric involvement of other small joints (MCPs, PIPs, wrists, MTPs), as symmetric polyarthritis is characteristic of rheumatoid arthritis. 5, 9, 8

Essential Laboratory Workup

First-Line Tests

• Inflammatory markers: Order CRP (preferred over ESR as it is more reliable and not age-dependent) and ESR to quantify systemic inflammation. 5, 4
• Rheumatoid factor (RF) and anti-CCP antibodies: Anti-CCP has 90% specificity and 60% sensitivity for rheumatoid arthritis; RF has 70% specificity with similar sensitivity. 5, 9, 7
• Complete blood count with differential to assess for cytopenias and calculate neutrophil-to-lymphocyte ratio before starting treatment. 5
• Comprehensive metabolic panel including liver function tests, renal function, glucose, and urate levels for baseline assessment and to exclude gout. 5, 4
• Serum uric acid: Normal uric acid effectively excludes gout as the primary diagnosis. 1, 5

Conditional Testing Based on Clinical Presentation

• Antinuclear antibodies (ANA) if diagnosis remains uncertain to screen for systemic lupus erythematosus or other connective tissue diseases. 5, 4
• HLA-B27 testing if symptoms suggest reactive arthritis, affect the spine, or spondyloarthropathy is suspected. 5, 4
• Hepatitis B, Hepatitis C, and tuberculosis screening before starting any biologic therapy if inflammatory arthritis is confirmed. 5

Imaging Studies

Initial Imaging

• Plain radiographs of the right hand (PA and lateral views) are the standard initial imaging to assess for erosions, periarticular osteopenia, uniform joint space narrowing, and osseous erosions characteristic of rheumatoid arthritis. 5, 7, 8
• Presence of erosions on baseline radiographs is highly predictive for rheumatoid arthritis diagnosis and disease persistence. 5

Advanced Imaging When Diagnosis Uncertain

• Ultrasound with Power Doppler is superior to clinical examination for detecting synovitis and structural damage, and can detect subclinical inflammation that predicts disease progression even when physical examination is normal. 5, 7
• MRI with IV contrast is more sensitive than ultrasound in early stages and detects bone marrow edema (osteitis), which is the best single predictor of future disease progression and functional deterioration. 5
• Power Doppler ultrasound is particularly useful when patients with early arthritis do not meet the 2010 ACR/EULAR criteria for rheumatoid arthritis. 5

Differential Diagnosis Algorithm

If Monoarticular MCP Swelling with Acute Onset

1. Septic arthritis (most critical)—perform arthrocentesis immediately. 1, 2, 3
2. Crystal arthropathy (gout or pseudogout)—check serum uric acid and synovial fluid for crystals. 1, 4
3. Trauma with retained foreign body—if history of puncture wound, obtain radiographs first; if negative, use ultrasound or CT for radiolucent material (wood, plastic). 1

If Symmetric Polyarticular Involvement

1. Rheumatoid arthritis—most likely if symmetric small joint involvement, morning stiffness >30 minutes, positive RF/anti-CCP, elevated CRP/ESR. 5, 9, 7, 8
2. Psoriatic arthritis—examine skin for psoriatic plaques or nail changes (pitting, onycholysis); can be RF/anti-CCP negative. 5
3. Adult-onset Still's disease—consider if high-spiking fevers, salmon-pink evanescent rash, and markedly elevated ferritin (>1,000 ng/mL). 1, 5

If Migratory Pattern

1. Acute rheumatic fever—check antistreptolysin O titer and throat culture; migratory polyarthritis of large joints is a hallmark. 6
2. Disseminated gonococcal infection—obtain urethral/cervical cultures and blood cultures. 6
3. Viral arthritis (parvovirus B19, hepatitis B/C, EBV)—symptoms resolving within 6 weeks suggest viral cause. 5

Management Based on Diagnosis

If Septic Arthritis Confirmed

• Initiate IV antibiotics immediately after obtaining cultures; do not delay for culture results. 1, 2
• Surgical drainage or serial arthrocentesis may be required. 1

If Rheumatoid Arthritis Confirmed (Score ≥6/10 on ACR/EULAR Criteria)

• Start methotrexate 15 mg weekly immediately as first-line DMARD without delaying for complete serologic workup, as early treatment prevents irreversible joint damage. 5, 9
• Plan to escalate to 20-25 mg weekly based on response. 5
• Consider short-term low-dose prednisone (10-20 mg daily) as bridge therapy while awaiting DMARD effect. 5
• Target remission (SDAI ≤3.3) or low disease activity (SDAI ≤11) with reassessment every 4-6 weeks. 5

If Diagnosis Uncertain but High Suspicion for Inflammatory Arthritis

• Refer to rheumatology within 6 weeks of symptom onset, as earlier treatment initiation leads to better outcomes. 5, 6, 9
• Consider ultrasound with Power Doppler or MRI to detect subclinical synovitis. 5, 7

Critical Pitfalls to Avoid

• Never inject corticosteroids into a swollen joint until infection is completely excluded by synovial fluid analysis. 2
• Do not delay treatment waiting for positive serology—seronegative rheumatoid arthritis accounts for 20-30% of cases and has similar prognosis to seropositive disease. 5
• Do not dismiss inflammatory arthritis based on normal ESR/CRP—acute phase reactants can be normal even in active disease and are poor predictors with only 50% sensitivity. 5
• Do not assume osteoarthritis in a single swollen MCP—osteoarthritis typically affects DIPs and first CMC joints while sparing MCPs. 5, 8