What is the differential diagnosis and treatment for an elderly patient with a painful, inflamed and red great toe, difficulty weight-bearing, and recent history of community-acquired pneumonia and fluid overload?

Acute Painful Great Toe in Elderly Patient Post-Hospitalization

The most likely diagnosis is acute gout (podagra), but you must urgently rule out septic arthritis through joint aspiration before initiating treatment, as bacterial infection can coexist with gout and requires immediate different management to prevent joint destruction and sepsis. 1

Differential Diagnosis

Primary Considerations

Acute Gout (Most Likely)

• Classic presentation: acute onset (<24 hours), severe pain, erythema, warmth, and swelling of the great toe (podagra) 2
• Risk factors present in this patient: recent hospitalization, fluid overload treatment (likely diuretics), community-acquired pneumonia (metabolic stress) 2
• Can present with fluctuant, abscess-like appearance despite being crystalline disease 2

Septic Arthritis (Must Exclude)

• Recent hospitalization increases risk of bacterial seeding, particularly with Staphylococcus aureus 1
• Can coexist with gout in up to 5% of cases—this is a critical diagnostic pitfall 1
• Presents identically to gout: red, hot, swollen joint with severe pain 1

Cellulitis/Soft Tissue Infection

• Recent hospitalization and fluid overload create risk for skin breakdown 3
• Less common organisms like Proteus mirabilis possible in elderly with vascular compromise 3
• Typically more diffuse than monoarticular involvement 4

Charcot Neuro-osteoarthropathy (If Diabetic)

• Unilateral foot redness, warmth, swelling in diabetic patients 5
• May have minimal pain due to neuropathy—absence of severe pain would favor this over gout 5
• Requires immediate immobilization while awaiting imaging 5

Immediate Diagnostic Workup

Mandatory First Step: Joint Aspiration

Perform arthrocentesis of the first metatarsophalangeal joint before any treatment 1

• Send synovial fluid for:
  • Cell count with differential (>50,000 WBC/μL suggests septic arthritis) 1
  • Gram stain and culture (aerobic and anaerobic) 4
  • Polarized light microscopy for monosodium urate crystals (needle-shaped, negatively birefringent) 2, 1
• Critical pitfall: The presence of urate crystals does NOT exclude infection—both can coexist 1

Laboratory Studies

• Serum uric acid (may be normal during acute attack) 2
• Complete blood count (elevated WBC suggests infection) 4
• Inflammatory markers: ESR, CRP (elevated in both gout and infection) 4
• Blood cultures if systemically ill or fever present 4
• Renal function (creatinine, BUN) to guide medication dosing 6

Imaging

• Plain radiographs of the foot: obtain immediately 5
  • Look for bone destruction (osteomyelitis), gas in soft tissues, or chronic tophaceous changes 4
  • Early osteomyelitis may not be visible 4
• MRI if diagnosis unclear: most accurate for detecting osteomyelitis and deep soft tissue infection 4

Assess for Diabetes

• If not known diabetic: check fasting glucose and HbA1c 5
• If diabetic: perform 10-g monofilament test and check for neuropathy 5
• Measure temperature difference between feet (≥2°C suggests Charcot) 5

Treatment Algorithm

If Septic Arthritis Confirmed or Cannot Be Excluded

Immediate empiric antibiotics (do not wait for culture results):

• Vancomycin 15-20 mg/kg IV every 8-12 hours (covers MRSA) PLUS
• Ceftriaxone 2g IV daily or cefepime 2g IV every 8 hours (covers gram-negatives) 4
• Adjust based on renal function 6
• Duration: minimum 2-4 weeks, often 4-6 weeks if bone involvement 4
• Urgent orthopedic consultation for possible surgical drainage 4

If Gout Confirmed (Crystals Present, Infection Excluded)

First-line treatment options (choose based on contraindications):

Colchicine (preferred if no contraindications):

• Loading dose: 1.2 mg PO immediately, then 0.6 mg one hour later 6
• Do NOT repeat this course for at least 2 weeks 6
• Adjust for renal impairment:
  • CrCl 30-50 mL/min: monitor closely, no dose adjustment needed 6
  • CrCl <30 mL/min: single dose 0.6 mg, do not repeat for 2 weeks 6
  • Dialysis: 0.6 mg once, do not repeat for 2 weeks 6
• Critical drug interaction warning: Avoid with clarithromycin, erythromycin, or other CYP3A4 inhibitors—can cause fatal rhabdomyolysis 7

NSAIDs (if colchicine contraindicated):

• Indomethacin 50 mg PO three times daily until resolution, then taper 2
• Avoid if: renal impairment (CrCl <30), heart failure, recent GI bleeding 2

Corticosteroids (if both above contraindicated):

• Prednisone 30-40 mg PO daily for 5-7 days, then taper 2
• Only use after infection definitively excluded 1
• Intra-articular injection (triamcinolone 20-40 mg) is alternative if monoarticular 2

Supportive Care

• Rest and elevate affected foot 4
• Ice application for comfort 2
• Adequate hydration 4
• Analgesia: acetaminophen for pain (avoid opioids if possible) 4

Common Pitfalls to Avoid

1. Starting gout treatment without excluding infection: Steroids or NSAIDs given for presumed gout when infection present can lead to rapid joint destruction and sepsis 1

2. Assuming crystals exclude infection: Up to 5% of septic joints have concurrent crystal disease 1

3. Using clarithromycin or other macrolides with colchicine: This combination can cause fatal rhabdomyolysis within days 7

4. Not adjusting colchicine dose for renal impairment: Patient has recent fluid overload suggesting possible renal compromise—overdosing causes severe toxicity 6

5. Failing to immobilize if diabetic with Charcot: Delayed immobilization allows irreversible bone destruction 5

6. Treating empirically without joint aspiration in elderly: Elderly patients with comorbidities have higher risk of atypical presentations and concurrent infections 1, 3

Follow-Up

• Reassess at 48-72 hours for clinical improvement 4
• If no improvement: reconsider diagnosis, check culture results, evaluate for osteomyelitis with MRI 4
• Once acute attack resolves: initiate urate-lowering therapy (allopurinol) for secondary prevention if recurrent gout 8
• Do not start allopurinol during acute attack—wait 2-4 weeks after resolution 8