Arthritis - Approach

• First step to to determine extent of involvement: mono vs oligo vs polyarthritis
• Monoarthritis:
  • Differential diagnosis
• Trauma: hemarthrosis, fracture, ligamentous injury
• Infection: staphylococcus, streptococcus, neisseria, GNRs, TB, fungal, Lyme
• Crystal: gout, pseudogout
• Rheumatologic: seronegative spondylarthropathy, sarcoid, RA, OA
• History: assess timing, antecedent trauma, systemic complaints
• Exam: presence of synovitis (warmth, swelling, effusion), indicates that inflammatory process is present
  • Septic and crystal arthritis have nearly identical clinical features, and can occur concomitantly
  • Fever, leukocytosis, ESR, and CRP are non-specific (see attached JAMA article)
• Management: Given the difficulty in differentiating, aspiration should be performed in all joints with signs of inflammation
  • Aspiration: send cell count, GS, culture, crystals
    • Cell count:
      • >2K WBC/mm3 indicates inflammatory process
      • >50K WBC/mm3 suggests infection (+LR 7.7), with higher levels more strongly suggestive
        • However, this is not a clean dichotomy, and overlap exists
      • >90% PMNs also suggests infection (+LR 3.4)
  • Treatment:
    • Septic arthritis: joint should be drained urgently, then IV abx x 2 weeks, followed by PO
    • Pseudogout: intraarticular steroids and NSAIDs

(Christopher Woo MD, 11/1/10)