Msk Dermatology · Year 2 · from Msk Dermatology

Case 3: Diabetic Foot Osteomyelitis

Patient Presentation

Demographics: 62-year-old man

Chief Complaint: "The wound on my foot won't heal and it smells bad."

History of Present Illness: The patient has had a wound on the bottom of his right foot for approximately 3 months. It started as a small blister under the first metatarsal head that progressively enlarged. He has had intermittent drainage and recently noticed a foul odor. He has limited sensation in his feet and did not notice the wound until it was already significant. He has tried wound care at home with limited success.

Past Medical History:

• Type 2 diabetes mellitus for 20 years (poorly controlled, HbA1c 10.2%)
• Diabetic peripheral neuropathy
• Peripheral arterial disease
• Hypertension
• Chronic kidney disease stage 3

Medications:

• Insulin glargine 40 units at bedtime
• Insulin lispro sliding scale
• Lisinopril 40 mg daily
• Atorvastatin 40 mg daily
• Aspirin 81 mg daily

Social History:

• Former smoker (quit 2 years ago, 40 pack-year history)
• Works from home

Physical Examination

• Vital Signs: BP 148/88 mmHg, HR 84 bpm, Temp 37.4C
• General: Overweight, appears chronically ill
• Right Foot:
• 3 cm x 2 cm ulcer at first metatarsal head plantar surface
• Ulcer base with necrotic tissue and purulent drainage
• Foul odor
• Surrounding cellulitis extending 3 cm
• Probe-to-bone test: Positive (metal probe reaches bone through ulcer)
• Absent dorsalis pedis and posterior tibial pulses
• Monofilament sensation absent
• Left Foot: Calluses, no open wounds, absent pulses

Workup and Results

Laboratory Studies:

Wound Culture (deep tissue at time of debridement):

• Staphylococcus aureus (MRSA)
• Enterococcus faecalis
• Pseudomonas aeruginosa
• Bacteroides fragilis
• Polymicrobial infection

Imaging:

• Foot X-ray:
• Cortical erosion of first metatarsal head
• Periosteal reaction
• Soft tissue gas
• MRI Foot:
• First metatarsal osteomyelitis with marrow edema
• Surrounding soft tissue abscess
• Extent of infection mapped for surgical planning
• Ankle-Brachial Index: 0.5 right, 0.6 left (severe PAD)

Diagnosis

Diabetic Foot Osteomyelitis (First Metatarsal) with Polymicrobial Infection and Severe Peripheral Arterial Disease

Key Diagnostic Features:

• Positive probe-to-bone test (PPV >85% when pre-test probability high)
• Radiographic bone destruction
• MRI confirmation
• Polymicrobial wound culture typical of diabetic foot infection

Treatment Plan

Multidisciplinary Approach:

1. Vascular surgery consultation: Assess revascularization options (severe PAD limits wound healing and antibiotic delivery)
2. Infectious disease consultation: Antibiotic management
3. Podiatry/Orthopedic surgery: Surgical debridement

Vascular Assessment:

• Arterial duplex and possible angiography
• Consider revascularization (angioplasty, bypass) before definitive bone surgery

Antibiotic Therapy:

1. IV vancomycin 1g q12h (MRSA coverage, adjust for CKD)
2. IV piperacillin-tazobactam 3.375g q6h (gram-negative and anaerobic coverage, adjust for CKD)
3. Duration: 4-6 weeks after adequate surgical debridement
4. Narrow based on culture sensitivities when possible

Surgical Management:

1. Debridement of necrotic and infected tissue
2. Bone biopsy for culture confirmation
3. Possible partial first ray amputation if osteomyelitis cannot be adequately debrided
4. Wound VAC (vacuum-assisted closure) for wound management

Glycemic Control:

• Insulin drip or intensive insulin regimen while hospitalized
• Goal glucose 140-180 mg/dL

Offloading:

• Non-weight-bearing on affected foot
• Total contact cast or offloading device once wound healing

Teaching Points

1. Probe-to-bone test: If a sterile metal probe can reach bone through a diabetic foot ulcer, osteomyelitis is highly likely (sensitivity 66%, specificity 85%)
2. Polymicrobial infections: Diabetic foot osteomyelitis typically involves multiple organisms including S. aureus (often MRSA), gram-negatives, and anaerobes
3. Vascular assessment critical: Peripheral arterial disease must be addressed for wounds to heal; revascularization may be necessary before or concurrent with bone surgery
4. MRI vs. X-ray: MRI is more sensitive for early osteomyelitis; X-ray changes take 2-3 weeks to appear
5. Amputation consideration: Severe infection with inadequate blood supply may require amputation to save life; early aggressive management aims to avoid this outcome
6. Multidisciplinary team: Optimal outcomes require coordination between infectious disease, vascular surgery, podiatry/orthopedics, endocrinology, and wound care

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