What is the initial approach to a patient presenting with erythema (redness) and pain to the great toe?

Workup of Erythema and Pain to the Great Toe

The initial workup must immediately differentiate between infection (including diabetic foot infection and gout), inflammatory conditions (gout, erythema nodosum), vascular disorders (erythromelalgia), and trauma, as these require fundamentally different management approaches that directly impact morbidity and mortality.

Immediate Clinical Assessment

History - Key Elements to Elicit

• Diabetes status and duration: Loss of protective sensation, prior foot ulcers, or amputation history significantly increases infection risk 1
• Fever and systemic symptoms: Temperature >38°C, tachycardia, or elevated inflammatory markers suggest serious infection requiring urgent intervention 1
• Episodic vs. constant symptoms: Pain relieved by cooling suggests erythromelalgia, while constant pain with fever suggests infection 1, 2
• Trauma history: Recent injury, though patients with neuropathy may not recall trauma 1
• Medication history: Recent allopurinol initiation (especially with CKD) raises concern for drug hypersensitivity presenting with erythema and pain 1
• Systemic symptoms: Night sweats, weight loss, malaise suggest inflammatory conditions like erythema nodosum or underlying malignancy 3, 4

Physical Examination - Critical Findings

For diabetic patients or suspected infection:

• Assess protective sensation using Semmes-Weinstein 5.07 (10-g) monofilament 1
• Probe any ulcer to bone (PTB test) - positive test indicates osteomyelitis 1
• Measure erythema extent (>1.5 cm surrounding ulcer indicates infection) 1
• Check pedal pulses bilaterally and consider ankle-brachial index if pulses diminished 1
• Document presence of purulent discharge, warmth, and edema 1

For erythromelalgia:

• Bilateral involvement of feet/hands with episodic burning pain 1, 2
• Erythema and warmth that improves with local cooling 2
• Symptoms triggered by heat, exercise, or dependency 2

For inflammatory conditions:

• Tender subcutaneous nodules (1-5 cm) on anterior tibial areas suggest erythema nodosum 3, 4
• Symmetrical arthralgias without joint effusions 3

Initial Laboratory Workup

If infection suspected (especially in diabetics):

• Complete blood count (leukocytosis >15,000 suggests serious infection) 1
• C-reactive protein and ESR (CRP >260 mg/L indicates severe infection) 1
• Blood glucose and HbA1c 1
• Blood cultures before antibiotics 1
• Wound culture from ulcer base (not superficial swab) 1

If inflammatory condition suspected:

• Serum uric acid for gout 1
• Streptococcal serology, tuberculosis screening, chest X-ray for erythema nodosum 3, 4
• Consider inflammatory bowel disease workup if systemic symptoms present 3, 4

If allopurinol hypersensitivity suspected:

• Peripheral eosinophil count (>20% eosinophils suggests drug reaction) 1
• Liver function tests and creatinine 1
• Consider HLA-B*58:01 testing if available, particularly in Asian populations 1

Imaging Studies

Plain radiography of affected foot:

• Weight-bearing films to assess for osteomyelitis, fractures, or structural deformities 1
• Note: Early osteomyelitis may not be visible on plain films 1

Vascular studies if pulses diminished:

• Toe pressure measurement (normal >70 mmHg, <30 mmHg indicates critical ischemia) 1
• Toe-brachial index (TBI <0.7 warrants vascular referral) 1
• Arterial duplex ultrasound if significant peripheral arterial disease suspected 1

Immediate Management Based on Findings

If diabetic foot infection identified:

• Admit for IV antibiotics if systemic signs present (fever, leukocytosis, CRP >260) 1
• Obtain cultures before starting broad-spectrum antibiotics (amoxicillin-clavulanic acid IV initially) 1
• Urgent surgical debridement if no improvement within 24 hours 1
• Offloading and strict glycemic control 1

If erythromelalgia suspected:

• Avoid triggers (heat, exercise, prolonged dependency) 1, 2
• Limit cooling to maximum 10 minutes, 4 times daily to prevent tissue damage 1, 2
• Elevate extremities during episodes 2
• Trial aspirin 325 mg daily for 1 month (especially if myeloproliferative disorder suspected) 1
• Topical lidocaine 4-5% patches as first-line therapy 1, 2

If gout suspected:

• NSAIDs or colchicine for acute attack
• Avoid starting allopurinol during acute attack
• If patient recently started allopurinol and has rash with eosinophilia, immediately discontinue and consider drug hypersensitivity 1

Critical Pitfalls to Avoid

• Never dismiss erythema in diabetic patients as cellulitis without ruling out underlying ulcer or osteomyelitis - probe for depth and bone involvement 1
• Do not allow prolonged ice water immersion for erythromelalgia - this causes tissue damage and ulcerations despite symptom relief 1, 2
• Recognize allopurinol hypersensitivity early (rash + eosinophilia + fever) as it has 25% mortality if not promptly managed 1
• In diabetics with erythema and warmth, consider Charcot arthropathy in addition to infection, especially if foot appears "flattened" 1
• Assess vascular status before attributing all symptoms to infection - ischemia with superimposed infection has worse outcomes 1