How do you diagnose and differentiate between various types of arthritis, such as osteoarthritis, rheumatoid arthritis, and psoriatic arthritis, in patients with joint pain and stiffness, considering their age, medical history, and symptoms?

Diagnosing and Differentiating Types of Arthritis

Begin with a systematic clinical assessment focusing on specific joint distribution patterns, morning stiffness duration, and age of onset, followed by targeted laboratory testing including RF, anti-CCP, ESR/CRP, and plain radiographs to distinguish between osteoarthritis, rheumatoid arthritis, and psoriatic arthritis. 1, 2

Initial Clinical Assessment

Key Historical Features to Document:

• Age and gender: Advanced age and female gender predict rheumatoid arthritis (RA) 3
• Morning stiffness duration: >30 minutes suggests inflammatory arthritis rather than osteoarthritis (OA) 1
• Symptom duration: Document time from onset, as referral should occur within 6 weeks for inflammatory arthritis 1
• Joint distribution pattern:
  • Small joints of hands/feet with symmetrical involvement → RA 3
  • Distal interphalangeal (DIP) joints → OA or psoriatic arthritis (PsA) 4, 5
  • Metacarpophalangeal (MCP) joints and wrists → RA, gout, or hemochromatosis 4
  • Asymmetric "ray" pattern or dactylitis → PsA 4
• Axial/entheseal involvement: Suggests spondyloarthropathy including PsA 3
• Extra-articular features: Skin lesions (psoriasis), nail dystrophy, uveitis, or systemic symptoms 3

Physical Examination Specifics:

• Squeeze test: Compress MCP or metatarsophalangeal (MTP) joints—pain indicates inflammatory arthritis 1
• Palpable synovitis: Warm, swollen joints with boggy texture indicate active inflammation 1
• Joint count: Higher number of tender/swollen joints predicts RA 3
• Skin examination: Look for psoriatic plaques, nail pitting, or onycholysis for PsA 4

Essential Laboratory Testing

First-Line Panel (Order Together): 1, 2

• Complete blood count (CBC): Exclude infection, assess anemia of chronic disease
• ESR or CRP: Quantify inflammation; elevated levels predict persistent/erosive disease 3, 1
• Rheumatoid factor (RF): Interpret as negative (≤14-15 IU/mL), low positive (>ULN but ≤3× ULN), or high positive (>3× ULN) 1
• Anti-CCP antibodies: Critical for RA diagnosis; both RF and anti-CCP positivity predict severe disease 1
• Antinuclear antibodies (ANA): Screen for systemic lupus erythematosus and connective tissue diseases 1, 2
• Urinalysis and transaminases: Exclude non-rheumatologic diseases and assess systemic involvement 1

Additional Testing Based on Clinical Suspicion:

• HLA-B27: If axial symptoms or reactive arthritis suspected 2
• Serum urate: If gout suspected, particularly in MCP/wrist involvement 4
• Joint aspiration with synovial fluid analysis: Mandatory if septic arthritis or crystal arthropathy suspected—perform cell count, Gram stain, culture, and crystal analysis 1, 2

Common Pitfall: RF can be falsely positive in infections (mononucleosis, cytomegalovirus, parvovirus), other autoimmune diseases (Sjögren's, lupus, scleroderma), and vasculitis—always interpret with anti-CCP and clinical findings 1

Imaging Studies

Plain Radiographs (First-Line): 1, 2

• Obtain X-rays of hands and feet at baseline for all suspected inflammatory arthritis
• OA findings: Joint space narrowing, osteophytes, subchondral sclerosis, subchondral cysts 4, 5
• Erosive OA: Subchondral erosions with "gull-wing" deformities, primarily affecting DIP/PIP joints 4, 5
• RA findings: Periarticular osteoporosis, marginal erosions, symmetrical joint space narrowing in MCP/PIP/wrist 4
• PsA findings: Juxta-articular new bone formation, "pencil-in-cup" deformities, asymmetric distribution 4, 5

Advanced Imaging (When Indicated): 1, 2

• Ultrasound with power Doppler or MRI: Use when clinical examination is equivocal, to detect early synovitis not visible on plain films, or if symptoms persist despite treatment
• Ultrasound detects synovitis 2.18-fold more frequently than clinical examination 2
• MRI detects bone marrow edema, a strong predictor of radiographic progression 2

Differentiating Key Arthritis Types

Osteoarthritis

• Age: Often >50 years, but 30% diagnosed before age 45 6
• Pattern: DIP joints, first carpometacarpal joint, weight-bearing joints 5
• Morning stiffness: <30 minutes 1
• Labs: Normal RF, anti-CCP, ESR/CRP (unless erosive OA) 4
• X-ray: Osteophytes, joint space narrowing, no erosions (unless erosive variant) 4, 5

Rheumatoid Arthritis

• Demographics: Female predominance, advanced age 3
• Pattern: Symmetrical polyarthritis affecting MCP, PIP, wrists; spares DIP joints 4, 5
• Morning stiffness: >30 minutes, often hours 1
• Labs: RF and/or anti-CCP positive (high titers predict severe disease), elevated ESR/CRP 1
• X-ray: Periarticular osteoporosis, marginal erosions, symmetrical involvement 4

Psoriatic Arthritis

• Pattern: Asymmetric oligoarthritis, DIP involvement, dactylitis ("sausage digits"), or axial disease 3, 4
• Skin/nails: 80% have psoriasis before joint symptoms in children; examine for nail dystrophy 3, 4
• Labs: RF/anti-CCP typically negative; elevated ESR/CRP common 4, 7
• X-ray: Juxta-articular new bone formation, "pencil-in-cup" erosions, asymmetric distribution 4, 5
• Special consideration: Screen for uveitis (eye pain, redness, photophobia) 3

Erosive Osteoarthritis

• Pattern: Abrupt onset with marked pain, targets DIP/PIP joints 4
• Clinical: Inflammatory symptoms (swelling, erythema) despite being OA variant 4
• X-ray: Subchondral erosions with eventual bony fusion in 12-15% of cases 4, 5

Timing of Rheumatology Referral

Refer within 6 weeks of symptom onset if: 1, 2

• Arthritis involves >1 joint with swelling not caused by trauma or bony enlargement
• Positive squeeze test or palpable synovitis
• Morning stiffness >30 minutes
• Elevated inflammatory markers with compatible clinical picture

Earlier treatment initiation improves outcomes in inflammatory arthritis. 1

Initial Management Pending Rheumatology Consultation

• NSAIDs: Consider naproxen 500 mg twice daily after evaluating gastrointestinal, renal, and cardiovascular status 1
• Avoid DMARDs: Do not start methotrexate or other DMARDs until rheumatology consultation, as these require specialist-initiated monitoring protocols 1
• Screen for infections: Test for hepatitis B, C, and tuberculosis before starting immunosuppressive therapy 2

Monitoring After Diagnosis

• Serial rheumatologic examinations and inflammatory markers every 4-6 weeks after treatment initiation 1, 2
• Repeat radiographs within 1 year to assess disease progression 2
• Annual screening labs for patients on biologic treatment 1