What is the initial approach for a 66-year-old female with new onset polyarticular (multiple joint) pain in New England, including laboratory tests and potential treatments?

Initial Laboratory Workup for New Onset Polyarticular Joint Pain in a 66-Year-Old Female

Order the following initial laboratory panel: complete blood count (CBC), urinalysis, transaminases (liver enzymes), antinuclear antibodies (ANA), erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), rheumatoid factor (RF), and anti-cyclic citrullinated peptide (anti-CCP) antibodies. 1, 2

Essential Laboratory Tests

Core Screening Panel

• CBC, urinalysis, and transaminases are required to exclude non-rheumatologic diseases and assess for systemic involvement 1
• ANA testing helps identify systemic lupus erythematosus and other connective tissue diseases 1
• ESR or CRP quantifies the degree of inflammation and predicts persistent/erosive disease 1

Rheumatoid Arthritis-Specific Markers

• Rheumatoid factor (RF) should be measured and interpreted using ACR/EULAR criteria: negative (≤14-15 IU/mL), low positive (>ULN but ≤3× ULN), or high positive (>3× ULN) 2
• Anti-CCP antibodies are critical as both RF and anti-CCP positivity predict severe disease and poor prognosis 2
• These serologic markers contribute up to 3 points in the 2010 ACR/EULAR classification criteria for rheumatoid arthritis 2

Geographic Consideration: Lyme Disease in New England

Given the patient's location in New England, consider Lyme disease serology if there is a history of tick exposure, erythema migrans rash, or if the joint pain involves large joints (particularly the knee). 2 Lyme arthritis commonly presents as monoarticular or oligoarticular arthritis in endemic areas.

Clinical Context for Laboratory Interpretation

Number and Pattern of Joints Involved

• Swollen joints involving metacarpophalangeal (MCP) or metatarsophalangeal (MTP) joints strongly suggest inflammatory arthritis 1
• A positive "squeeze test" (pain with compression of MCP or MTP joints) indicates hand/foot joint involvement 1
• Morning stiffness >30 minutes supports inflammatory rather than mechanical causes 1

Timing of Rheumatology Referral

Refer to rheumatology within 6 weeks of symptom onset if arthritis involves more than one joint with swelling not caused by trauma or bony enlargement. 1 Earlier treatment initiation improves outcomes in inflammatory arthritis 1

Imaging Studies

Plain radiographs of affected joints are the initial imaging method of choice for suspected inflammatory arthritis. 1 X-rays establish baseline for erosive changes and help exclude other diagnoses.

Advanced imaging (ultrasound with power Doppler or MRI) complements radiographs when clinical examination is equivocal or to detect early synovitis not visible on plain films. 1

Common Pitfalls to Avoid

False Positive RF Results

• Infections (mononucleosis, cytomegalovirus, parvovirus) can cause false positive RF 2
• Other autoimmune diseases (Sjögren's syndrome, systemic lupus, systemic sclerosis) may have positive RF without rheumatoid arthritis 2
• Vasculitis of various vessel sizes can show RF positivity 2
• Always interpret RF in conjunction with anti-CCP and clinical findings 2

Distinguishing Inflammatory from Non-Inflammatory Pain

• Palpable synovitis (warm, swollen joints) indicates inflammation 1
• Bony hypertrophy and crepitus without warmth suggest osteoarthritis rather than inflammatory arthritis 3
• Inflammatory arthritis typically has systemic features (fever, weight loss, fatigue) that osteoarthritis lacks 3

Initial Symptomatic Management

While awaiting laboratory results and rheumatology evaluation:

NSAIDs (such as naproxen 500 mg twice daily) should be considered after evaluating gastrointestinal, renal, and cardiovascular status. 1, 4 Use the lowest effective dose for the shortest duration 4

Avoid starting DMARDs (like methotrexate) until rheumatology consultation, as these require specific monitoring protocols and should be initiated by specialists. 1, 5 However, patients at risk for persistent or erosive disease should start DMARDs as early as possible, even before meeting full classification criteria 1