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Difficulty: MediumInfectious Diseases

An evaluation is requested for a 67-year-old male patient who reports a persistent sore on the bottom of his right foot for the past two months. He has a 15-year history of type 2 diabetes mellitus complicated by peripheral neuropathy. His vital signs include a blood pressure of 135/85 mm Hg, a heart rate of 76/min, and a temperature of 37.0°C (98.6°F). On physical examination, there is a 2.5-cm, painless ulcer on the plantar aspect of the right first metatarsal head. There is no significant surrounding erythema, warmth, or fluctuance. During exploration of the wound, a sterile metallic probe easily contacts hard, gritty tissue at the base of the ulcer. Laboratory testing reveals a leukocyte count of 8,200/mm³ and an erythrocyte sedimentation rate of 95 mm/h. Radiography of the right foot demonstrates focal periosteal elevation and frank cortical erosion of the underlying metatarsal head. Which of the following is the most appropriate next step in the management of this patient?

  1. Perform a sterile bone biopsy for microbiologic cultureAnswer
  2. B
    Administer broad-spectrum intravenous antimicrobial therapy
  3. C
    Obtain a superficial swab of the ulcer exudate for culture
  4. D
    Obtain magnetic resonance imaging of the right foot
  5. E
    Proceed with urgent surgical amputation of the first metatarsal

Answer

Perform a sterile bone biopsy for microbiologic culture
The correct action is to perform a sterile bone biopsy. This patient has a confirmed case of diabetic foot osteomyelitis based on a positive probe-to-bone test and diagnostic plain radiographs showing cortical destruction. Because the patient is hemodynamically stable and has no systemic signs of severe infection (such as fever or extensive cellulitis), there is no indication for emergent empiric antibiotics. The standard of care is to withhold antimicrobial therapy until a bone biopsy can be obtained. This ensures accurate identification of the offending organism and its susceptibility profile, which is critical since diabetic foot infections are frequently polymicrobial or involve resistant organisms. Targeted therapy minimizes toxicity and adheres to principles of antimicrobial stewardship.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and diagnostic findings.
The patient has a chronic diabetic foot ulcer with a positive probe-to-bone test, elevated ESR, and plain radiograph findings of cortical erosion, which are collectively diagnostic of osteomyelitis.
Establishing a definitive diagnosis is required before determining the appropriate management pathway.
2
Assess the patient's hemodynamic stability and the urgency of treatment.
The patient is afebrile, normocardic, and lacks severe surrounding cellulitis or signs of sepsis.
Stable patients do not require emergent empiric antibiotics, allowing time for optimal diagnostic sampling.
3
Select the optimal diagnostic step to guide antimicrobial therapy.
A sterile bone biopsy is chosen over superficial swabs or empiric treatment.
Bone biopsy provides a definitive microbiologic diagnosis, allowing for targeted antimicrobial therapy in accordance with antibiotic stewardship principles.

Key Concept

In clinically stable patients with diabetic foot osteomyelitis, obtaining a deep tissue or bone biopsy for microbiologic culture prior to initiating antimicrobial therapy is essential to ensure targeted, effective treatment and prevent the selection of resistant organisms.
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Topics

Infectious Diseases

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