What could be causing a red and warm right great toe and how should it be treated?

Red and Warm Right Great Toe: Differential Diagnosis and Management

The most critical first step is to immediately rule out septic arthritis and gout through joint aspiration with synovial fluid analysis, as these conditions require urgent treatment to prevent joint destruction and systemic complications. 1

Immediate Diagnostic Priorities

The presentation of a red, warm great toe demands urgent evaluation for three life-altering conditions:

1. Septic Arthritis (Most Urgent)

• Send synovial fluid immediately for cell count with differential, Gram stain and culture, and polarized light microscopy for monosodium urate crystals. 1
• Obtain complete blood count, ESR, and CRP—these inflammatory markers are typically elevated in both infection and gout. 1
• Blood cultures should be drawn if fever or systemic illness is present. 1
• Start empiric antibiotics immediately with vancomycin plus ceftriaxone or cefepime if septic arthritis cannot be excluded—do not wait for culture results. 1
• Obtain urgent orthopedic consultation for possible surgical drainage if septic arthritis is confirmed. 1

2. Acute Gout

• Synovial fluid analysis with polarized light microscopy is the gold standard for diagnosing gout by identifying monosodium urate crystals. 1
• If gout is confirmed, colchicine is the preferred first-line treatment, though NSAIDs or corticosteroids may be used if colchicine is contraindicated. 1
• The presence of crystals does not exclude concurrent infection—both can coexist. 1

3. Charcot Neuro-Osteoarthropathy (If Diabetic)

• In any diabetic patient with neuropathy presenting with a unilateral red, warm, swollen foot, active Charcot must be suspected immediately. 2
• Measure temperature difference between both feet using infrared thermometry—a difference of ≥2°C strongly suggests active Charcot. 2, 3
• Initiate knee-high immobilization/offloading immediately while awaiting imaging—do not delay, as untreated Charcot leads to fractures, deformity, ulceration, and amputation. 2, 3
• Pain may be minimal or absent due to neuropathy, so never assume absence of pain rules out serious pathology. 2, 3
• The presence of ulceration or infection does not exclude underlying Charcot—both can coexist. 2

Imaging Strategy

• Obtain plain radiographs of the foot immediately to look for bone destruction, gas in soft tissues, chronic tophaceous changes, or fractures. 1
• MRI is the most accurate imaging modality for detecting osteomyelitis, deep soft tissue infection, and active Charcot neuro-osteoarthropathy when the diagnosis remains unclear. 2, 1
• In suspected Charcot, MRI shows bone marrow edema without fractures in stage 0 disease, though differentiating from osteomyelitis can be challenging and requires expert radiologist interpretation. 2

Secondary Differential Diagnoses

Cellulitis or Soft Tissue Infection

• Cellulitis typically presents with more diffuse involvement rather than monoarticular symptoms. 2, 1
• Diagnosis requires at least 2 classic signs of inflammation: erythema, warmth, swelling, tenderness/pain, or purulent secretions. 2
• In diabetic foot infections, gram-positive cocci (especially staphylococci) are the most common causative organisms. 2
• Wounds without evidence of soft tissue or bone infection do not require antibiotic therapy. 2

Allopurinol Hypersensitivity Syndrome (If Recently Started)

• This case report demonstrates that a red, swollen great toe can be part of allopurinol-induced hypersensitivity syndrome, which has a 25% mortality rate. 2
• Associated findings include fever, eosinophilia, rash, and elevated creatinine—particularly in patients with CKD who recently started allopurinol. 2
• The HLA-B*58:01 variant is strongly associated with this reaction (odds ratio 80-580:1). 2

Treatment Algorithm

Step 1: Perform joint aspiration immediately if monoarticular involvement is present. 1

Step 2: While awaiting synovial fluid results:

• If septic arthritis cannot be excluded, start vancomycin plus ceftriaxone/cefepime immediately. 1
• If diabetic with neuropathy, initiate knee-high immobilization regardless of other findings. 2, 3

Step 3: Definitive treatment based on diagnosis:

• Septic arthritis: Continue antibiotics and arrange surgical drainage. 1
• Gout: Start colchicine as first-line therapy. 1
• Charcot: Continue immobilization with total contact cast (gold standard) until temperature difference normalizes. 2
• Cellulitis: Debride any necrotic tissue and start appropriate antibiotics targeting gram-positive cocci. 2

Critical Pitfalls to Avoid

• Never delay immobilization in a diabetic patient with a hot, swollen foot while waiting for imaging—the consequences of untreated Charcot are devastating. 2, 3
• Do not assume absence of pain rules out serious pathology in diabetic patients with neuropathy. 2, 3
• Do not treat empirically for cellulitis without considering septic arthritis or gout in monoarticular involvement. 1
• In diabetic patients, the presence of infection or ulceration does not exclude underlying Charcot—both conditions can coexist. 2

Follow-Up and Reassessment

• Reassess at 48-72 hours for clinical improvement—if no improvement, reconsider the diagnosis and check culture results. 1
• If osteomyelitis is suspected based on lack of improvement or imaging findings, perform MRI to evaluate extent of infection. 1
• For confirmed Charcot, monitor temperature differences weekly and continue immobilization until the difference is <2°C for at least 2 consecutive weeks. 2