MKSAP quiz: Foot ulcer management
This month's quiz asks readers to choose a next step in management for a 57-year-old man with a nonhealing ulcer on the plantar aspect of the left foot despite six weeks of standard wound care and pressure off-loading.
A 57-year-old man is evaluated for a nonhealing ulcer on the plantar aspect of the left foot despite 6 weeks of standard wound care and pressure off-loading. Medical history is significant for type 2 diabetes, hypertension, and coronary artery disease. Medications are metformin, canagliflozin, metoprolol, enalapril, atorvastatin, and aspirin.
On physical examination, vital signs are normal. A 2.5-×2.5-cm ulcer is located on the plantar aspect of the left foot in the region of the first metatarsal head. Erythema is noted along the ulcer edge without evidence of cellulitis. The ulcer base has a significant amount of purulent material. A probe-to-bone test is positive.
Which of the following is the most appropriate management?
A. Bone biopsy
B. Cephalexin
C. MRI
D. Plain radiography
MKSAP Answer and Critique
The correct answer is D. Plain radiography. This item is available to MKSAP 19 subscribers as item 5 in Extension Set 1 of the Infectious Disease section. More information about MKSAP is online.
The patient should undergo plain radiography of the foot to evaluate for osteomyelitis (Option D). The possibility of underlying osteomyelitis must be considered with this ulcer greater than 2 cm in diameter that has not improved over 6 weeks of standard care. In the setting of a purulent (infected) ulcer base, the positive predictive value of the probe-to-bone test is high; however, imaging should be performed to confirm the diagnosis and assess the extent of bone involvement. Plain radiographs are more cost effective than other imaging modalities, and positive findings are highly specific for osteomyelitis. The characteristic radiographic findings of osteomyelitis include soft tissue swelling, osteopenia, cortical loss, bony destruction, and periosteal reaction.
Imaging to confirm the diagnosis and to assess the extent of bone involvement should be performed before obtaining a bone biopsy (Option A) in the setting of possible osteomyelitis.
Empiric antibiotic therapy is not indicated at this time because the patient has normal vital signs and no evidence of cellulitis. A bone biopsy and culture should be obtained before antibiotic therapy if the radiograph confirms a diagnosis of osteomyelitis. Empiric antibiotics before biopsy could decrease the microbiologic yield of a bone biopsy. If the patient had cellulitis or he required empiric therapy for a mild or moderately severe diabetic foot ulcer, cephalexin would be a good choice for therapy (Option B). However, he does not have cellulitis, so empiric therapy before bone biopsy and culture is not indicated, and initiating cephalexin is not appropriate.
The sensitivity of plain radiography is not adequate to exclude the diagnosis of osteomyelitis. Therefore, if the radiograph is negative, contrast-enhanced MRI would be the next step in the evaluation (Option C).
Key Point
- Imaging should be performed in patients with high suspicion of osteomyelitis to confirm the diagnosis and assess the extent of bone involvement; plain radiographs are more cost effective than other imaging modalities and have high specificity for osteomyelitis.