Algorithm for Assessing Arthritis Based on Number of Joints Involved
Step 1: Confirm True Articular Pain vs. Periarticular Disease
Palpate for synovitis (soft, boggy joint swelling) rather than bony enlargement or periarticular tenderness. 1, 2 A positive "squeeze test" (pain with compression of metacarpophalangeal or metatarsophalangeal joints) indicates true joint inflammation. 1
Step 2: Classify as Inflammatory vs. Non-Inflammatory
Inflammatory Arthritis Features:
- Morning stiffness ≥30 minutes (ideally ≥1 hour) 1, 3, 4
- Warm, swollen joints with palpable synovitis 1, 2
- Improvement with activity 2, 5
- Systemic symptoms (fatigue, fever, weight loss) 4, 6
Non-Inflammatory Arthritis Features:
- Morning stiffness <30 minutes 1, 2
- Bony hypertrophy and crepitus 2, 6
- Pain worsens with activity, improves with rest 2, 5
- No systemic symptoms 5
Step 3: Categorize by Number of Joints Involved
Monoarticular (1 joint):
- First priority: Rule out septic arthritis and crystal arthropathy 1
- Perform joint aspiration with synovial fluid analysis (cell count, Gram stain, culture, crystal analysis) 1
Oligoarticular (2-4 joints):
- Consider spondyloarthropathies (psoriatic arthritis, reactive arthritis, ankylosing spondylitis) 1, 2
- Look for asymmetric distribution, DIP involvement, dactylitis, or axial symptoms 1
- Order HLA-B27 if axial pain, enthesitis, or reactive arthritis suspected 1, 3
Polyarticular (≥5 joints):
- Proceed to Step 4 for detailed differential diagnosis algorithm
Step 4: Polyarticular Inflammatory Arthritis—Apply Joint Distribution Pattern
A. Symmetric Small Joint Involvement (MCPs, PIPs, wrists, MTPs):
Most likely diagnosis: Rheumatoid Arthritis 1, 3, 4
Immediate workup:
- Serology: RF and anti-CCP antibodies (order simultaneously) 1, 3
- Inflammatory markers: ESR and CRP (CRP preferred for monitoring) 1, 3, 2
- Baseline labs: CBC with differential, comprehensive metabolic panel, urinalysis 1, 3
- Imaging: Bilateral hand, wrist, and foot X-rays to assess for erosions 1, 3, 2
Apply 2010 ACR/EULAR Classification Criteria (score ≥6/10 = definite RA): 3, 2
| Domain | Scoring |
|---|---|
| Joint involvement | 1 large joint = 0 pts; 2-10 large = 1 pt; 1-3 small = 2 pts; 4-10 small = 3 pts; >10 joints = 5 pts [3,2] |
| Serology | Negative RF & anti-CCP = 0 pts; Low positive = 2 pts; High positive = 3 pts [3,2] |
| Acute phase reactants | Normal CRP & ESR = 0 pts; Abnormal = 1 pt [3,2] |
| Symptom duration | <6 weeks = 0 pts; ≥6 weeks = 1 pt [3,2] |
Refer to rheumatology within 6 weeks of symptom onset if score ≥6 or high clinical suspicion. 1, 3 Early treatment prevents irreversible joint damage. 1, 3
B. Asymmetric Oligoarthritis with DIP Involvement, Dactylitis, or Nail Changes:
Most likely diagnosis: Psoriatic Arthritis 1, 2
Key distinguishing features:
- DIP joint involvement (RA typically spares DIPs) 1, 3
- Dactylitis ("sausage digits") 1
- Nail pitting, onycholysis 1, 2
- Psoriatic skin plaques 1, 2
- Typically anti-CCP negative 1, 3
Workup:
- RF and anti-CCP (usually negative) 1
- ESR/CRP (may be elevated) 1, 2
- HLA-B27 if axial involvement 1
- X-rays of affected joints 2
- Skin and nail examination mandatory 1, 2
C. Axial Pain + Peripheral Arthritis (Especially Lower Extremity):
Consider: Spondyloarthropathies (Ankylosing Spondylitis, Reactive Arthritis) 1, 2
Red flags for axial spondyloarthropathy:
- Age <45 years with low back pain >3 months 7
- Pain worse in latter part of night 7
- Morning stiffness >30 minutes 7
- Improves with exercise, not relieved by rest 7
Workup:
- HLA-B27 testing 1, 3
- MRI of spine (sagittal T1 and STIR images) and sacroiliac joints (coronal/oblique T1 and STIR) 7
- Plain radiographs miss most early disease 7
- ESR/CRP 1, 2
- History of recent GI/GU infection or uveitis 1
Refer to rheumatology early—sulfasalazine and methotrexate are NOT effective for axial disease; anti-TNF agents often required. 7
D. Polyarticular Arthritis with Systemic Features (Fever, Rash, Serositis):
Consider: Systemic Lupus Erythematosus, Adult-Onset Still's Disease, Viral Arthritis 3, 6
Workup:
- ANA with reflex to anti-dsDNA and ENA panel if positive 1, 3
- Note: Symmetric polyarthritis with elevated CRP is more typical of RA than SLE 3
- Serum ferritin (>1,000 ng/mL suggests Adult-Onset Still's Disease) 3
- Viral serologies (parvovirus B19, hepatitis B/C, EBV) if acute onset 3
- Viral arthritis typically resolves within 6 weeks 3
- CBC, urinalysis, comprehensive metabolic panel 1, 3
Step 5: Advanced Imaging When Diagnosis Uncertain
If clinical examination is equivocal but suspicion for inflammatory arthritis remains high: 1, 3
- Ultrasound with Power Doppler: Detects subclinical synovitis; 75% more accurate than physical examination alone 1, 3
- MRI with IV contrast: Most sensitive for early disease; detects bone marrow edema (osteitis), the strongest predictor of future erosive progression 1, 3
Step 6: Exclude Mimics and Non-Rheumatologic Causes
Common Pitfalls:
- Infections causing false-positive RF: Mononucleosis, CMV, parvovirus, hepatitis B/C 1
- Other autoimmune diseases with positive RF: Sjögren's syndrome, SLE, systemic sclerosis, vasculitis 1
- Polymyalgia rheumatica: Proximal muscle pain without true weakness, normal CK, no definite synovitis 3
- Osteoarthritis: Can coexist with inflammatory arthritis; look for bony enlargement vs. soft tissue swelling 1, 2
Always interpret RF and anti-CCP in conjunction with clinical findings—do not rely on serology alone. 1, 3
Step 7: Initial Management While Awaiting Rheumatology Referral
Symptomatic Treatment:
- NSAIDs (e.g., naproxen 500 mg twice daily) after evaluating GI, renal, and cardiovascular status 1
- Avoid starting DMARDs (methotrexate) until rheumatology consultation 1
Pre-DMARD Screening (if RA confirmed):
- Hepatitis B, hepatitis C, tuberculosis screening before biologic therapy 1, 3
- Baseline CBC, comprehensive metabolic panel, urinalysis 1, 3
Summary Algorithm Flowchart
Joint Pain → Confirm True Articular Pain (palpate for synovitis)
↓
Inflammatory Features? (morning stiffness ≥30 min, warm/swollen joints)
↓
YES → Count Joints Involved
↓
1 joint → Aspirate (rule out septic/crystal arthritis)
2-4 joints → Consider spondyloarthropathies (check HLA-B27, skin/nail exam)
≥5 joints → Assess Distribution Pattern:
↓
Symmetric small joints (MCPs, PIPs, wrists, MTPs)
→ Order RF, anti-CCP, ESR/CRP, X-rays
→ Apply 2010 ACR/EULAR criteria
→ Refer rheumatology within 6 weeks if score ≥6
↓
Asymmetric + DIP/dactylitis/nail changes
→ Psoriatic arthritis (skin exam, HLA-B27 if axial)
↓
Axial pain + peripheral arthritis
→ Spondyloarthropathy (HLA-B27, MRI spine/SI joints)
↓
Systemic features (fever, rash)
→ ANA, ferritin, viral serologiesCritical pearl: Do NOT delay treatment waiting for positive serology—seronegative RA is common and has similar prognosis. 3 Do NOT dismiss diagnosis based on normal ESR/CRP—acute phase reactants can be normal even in active inflammatory arthritis. 3