What is the most appropriate initial assessment for a diabetic patient with a foot ulcer, toe swelling, and discharge?

Initial Assessment of Diabetic Foot Ulcer with Infection

The most appropriate initial assessment is none of the imaging options listed—instead, perform bedside clinical evaluation including probe-to-bone test, obtain vital signs and blood tests, perform surgical debridement with tissue culture, and obtain plain X-rays of the foot. 1

Immediate Clinical Assessment Steps

1. Wound Evaluation and Infection Severity

• Debride the ulcer to visualize the full extent of tissue involvement and remove callus/necrotic tissue 1
• Perform probe-to-bone test at the ulcer base using a sterile metal probe—if bone is palpable, this strongly suggests osteomyelitis in this high-risk patient with discharge 1
• Assess infection severity by measuring extent of cellulitis (>2 cm from ulcer edge indicates moderate-to-severe infection), checking for systemic signs (fever, tachycardia, hypotension), and looking for deep tissue involvement 1
• Obtain vital signs and blood tests including complete blood count, inflammatory markers (ESR, CRP), and blood glucose 1

2. Obtain Tissue Culture (Not Swab)

• Collect tissue specimens from the debrided wound base using curettage or biopsy—this is critical as superficial swabs yield unreliable results with contaminants 1
• If osteomyelitis is suspected based on probe-to-bone test, obtain bone biopsy (percutaneously or surgically) for culture and histology to guide antibiotic therapy 1
• Avoid using wound swabs or sinus tract specimens as they do not accurately reflect the causative pathogens 1

3. Plain Radiographs First

• Obtain plain X-rays of the foot as the initial imaging study for all non-superficial diabetic foot infections 1
• Look for bone destruction, periosteal reaction, or gas in soft tissues 1
• If plain films are negative but clinical suspicion for osteomyelitis remains high (positive probe-to-bone, elevated ESR >70 mm/hr), proceed to MRI 1

4. Vascular Assessment

• Palpate distal pulses (dorsalis pedis and posterior tibial)—you note these are intact, which is reassuring 1
• However, palpable pulses do not reliably exclude peripheral artery disease (PAD) 1
• Perform bedside vascular testing: measure ankle-brachial index (ABI 0.9-1.3 suggests adequate perfusion), toe-brachial index (TBI ≥0.75 excludes significant PAD), or assess Doppler waveforms (triphasic signals exclude PAD) 1
• Since pulses are intact, advanced vascular imaging (duplex US, angiography, MRA, or CT angiography) is not indicated initially unless bedside tests suggest ischemia 1

Why the Listed Options Are Not First-Line

None of the imaging modalities (A-D) are the most appropriate initial assessment:

• Duplex ultrasound, conventional angiography, MRA, and CT angiography are reserved for anatomical vascular assessment only when bedside tests indicate significant ischemia (toe pressure <30 mmHg, ankle pressure <50 mmHg, ABI <0.5, or TcPO2 <25 mmHg) requiring revascularization 1
• With intact distal pulses, the priority is infection control and wound assessment, not vascular imaging 1
• If vascular imaging becomes necessary later (non-healing ulcer after 6 weeks despite optimal management), any of these modalities can be used, but this is not the initial step 1

Advanced Imaging for Osteomyelitis (If Needed)

• MRI is the preferred advanced imaging if osteomyelitis diagnosis remains uncertain after clinical assessment and plain X-rays 1
• MRI has 82-100% sensitivity and 75-96% specificity for osteomyelitis 2
• Alternative imaging (labeled WBC scan, SPECT/CT, or PET/CT) only if MRI is contraindicated or unavailable 1

Common Pitfalls to Avoid

• Do not rely on superficial wound swabs for culture—they lead to inappropriate antibiotic selection and treatment failure 1
• Do not assume adequate perfusion based solely on palpable pulses—perform objective bedside vascular testing 1
• Do not delay surgical debridement when purulent discharge is present—"don't let the sun set on pus" 1
• Do not order vascular imaging without first performing bedside vascular assessment in a patient with intact pulses 1

Treatment Priorities After Assessment

• Initiate empiric antibiotics covering gram-positive cocci (including MRSA if risk factors present) and gram-negative organisms for moderate-to-severe infections 1
• Surgical consultation for debridement if moderate-to-severe infection, deep abscess, or necrotizing infection 1
• Pressure off-loading with total contact cast or removable walker once infection is controlled 1
• Reassess in 48-72 hours and adjust antibiotics based on culture results 1