What is the approach to diagnose and treat a patient with a potentially inflamed big toe, suspected of having gout or cellulitis?

How to Aspirate a Big Toe for Possible Gout versus Cellulitis

Synovial fluid aspiration and examination for crystals is strongly recommended in any patient with undiagnosed inflammatory arthritis, including suspected gout in the big toe. 1

Diagnostic Approach

Step 1: Clinical Assessment

• Differentiate between gout and cellulitis based on clinical presentation:
  • Gout typically presents with rapid onset of severe pain and swelling (at its worst in <24 hours), erythema, and often involves the first metatarsophalangeal (MTP) joint 1
  • Cellulitis typically presents with more gradually developing erythema, warmth, swelling, and tenderness without the same intense joint pain 1
  • Both conditions can present with similar symptoms, making definitive diagnosis through aspiration necessary 2

Step 2: Aspiration Technique

1. Preparation:

   • Position the patient with the foot accessible and supported 1
   • Clean the area with antiseptic solution (chlorhexidine or povidone-iodine) 1
   • Use sterile gloves, mask, and appropriate personal protective equipment 1

2. Aspiration procedure:

   • For first MTP joint (podagra):
     • Insert a 22-25 gauge needle attached to a 3-5 mL syringe from the dorsomedial or dorsolateral aspect of the joint 1
     • Direct the needle toward the joint space between the metatarsal head and proximal phalanx 1
     • Apply gentle suction while slightly repositioning the needle if no fluid is obtained initially 1
   • For suspected cellulitis without clear joint involvement:
     • Skin aspiration may be performed at the advancing edge of erythema 1
     • Note that skin aspiration for cellulitis has low sensitivity but may yield aerobic gram-positive cocci if positive 1

3. Specimen handling:

   • Transfer synovial fluid to appropriate containers:
     • Sterile tube for crystal analysis (no additives) 1
     • Culture tubes if infection is suspected 1
   • Examine fluid promptly for monosodium urate (MSU) crystals using polarized microscopy 1

Step 3: Interpretation of Results

• Gout diagnosis:

  • Presence of needle-shaped, negatively birefringent MSU crystals is diagnostic for gout 1, 3
  • Hyperuricemia alone is insufficient for diagnosis 1

• Cellulitis diagnosis:

  • Cultures showing bacterial growth (typically streptococci or Staphylococcus aureus) 1
  • Absence of crystals with signs of infection 1

• If aspiration is not possible or inconclusive:

  • Consider imaging (ultrasound can detect double contour sign specific for urate deposits) 1
  • Clinical features may guide presumptive diagnosis and treatment 1, 4

Management Based on Diagnosis

For Gout:

• Acute treatment with colchicine, NSAIDs, or corticosteroids 5, 6
• Consider urate-lowering therapy for recurrent attacks 6

For Cellulitis:

• Antimicrobial therapy active against streptococci for typical cases 1
• For severe cases or those with risk factors for MRSA, consider vancomycin or other MRSA-active agents 1
• Standard duration is 5 days, extended if not improved 1

Common Pitfalls and Caveats

• Diagnostic challenges:

  • Gout can mimic cellulitis and vice versa; they can also coexist 4, 2
  • Inadequate aspiration technique may yield false-negative results 1
  • Delayed analysis of synovial fluid may lead to crystal dissolution 1

• Procedural considerations:

  • Use adequate local anesthesia to minimize patient discomfort 1
  • Avoid aspiration through cellulitic skin when possible 1
  • Consider ultrasound guidance for difficult aspirations 1

• Post-procedure care:

  • Apply pressure to aspiration site to prevent bleeding 1
  • Monitor for signs of infection at the aspiration site 1
  • Provide appropriate analgesia while awaiting results 6

Remember that synovial fluid analysis with crystal identification is the gold standard for gout diagnosis, while culture remains essential for confirming infection 1.