MKSAP quiz: Expanding foot ulcer

This month's quiz asks readers about management of a 67-year-old patient with type 2 diabetes who is hospitalized with osteomyelitis.

A 67-year-old woman is hospitalized for an ulcer on the bottom of her right foot; it has expanded over the past 2 months. The patient has type 2 diabetes mellitus, hypertension, stage 3 chronic kidney disease, and peripheral neuropathy. Medications are insulin glargine, insulin lispro, lisinopril, and gabapentin.

On physical examination, temperature is 37.3 °C (99.1 °F); the remaining vital signs are normal. A deep 3- × 4-cm ulcer is located on the distal medial compartment of the plantar surface of the right foot. The base of the ulcer is necrotic and malodorous; a probe-to-bone test is negative. No surrounding erythema or increased warmth is noted. Both feet are warm with palpable pulses.

Erythrocyte sedimentation rate and C-reactive protein level are elevated. Results of a complete blood count are normal.

A plain radiograph reveals soft tissue swelling and ulceration; an MRI reveals findings consistent with osteomyelitis of the distal head of the first metatarsal.

Which of the following is the most appropriate management?

A. Bone biopsy and culture
B. Forefoot amputation
C. Swabbing and culture of wound base
D. Vancomycin and piperacillin-tazobactam

MKSAP Answer and Critique

The correct answer is A. Bone biopsy and culture. This item is available to MKSAP 18 subscribers as item 36 in the Infectious Disease section. More information about MKSAP 18 is available online.

A bone biopsy and culture is the next step in the management of osteomyelitis for this patient. Biopsies can be accomplished by open surgical procedure or percutaneously. Confirming a microbiologic diagnosis is needed before antibiotics can be administered.

Indications for amputation include persistent sepsis, inability to tolerate antibiotic therapy, progressive bone destruction despite therapy, and bone destruction that compromises the mechanical integrity of the foot. None of these indications are present in this patient. Surgical debridement of the ulcer may be needed to remove the necrotic tissue, but this can be done at the time of bone biopsy.

With the exception of Staphylococcus aureus, microorganisms isolated from culture samples obtained from superficial wounds or sinus tracts correlate poorly with deep cultures from bone; therefore, this practice is of limited value. Bone biopsy with histopathologic assessment and full microbiologic studies is important for diagnosing osteomyelitis, excluding other entities (such as neoplasm), and isolating the causative pathogen(s).

Because the patient has no signs of skin or soft tissue infection or of sepsis, antibiotics are not immediately needed; furthermore, the provision of empiric antibiotics would also decrease the yield of a subsequent bone biopsy. Vancomycin and piperacillin-tazobactam might be indicated in the future, pending the results of the bone biopsy. However, a histologic and microbiologic diagnosis confirmation is needed before antibiotics can be administered.

Key Point

  • Osteomyelitis in a patient with a diabetic foot infection and no evidence of skin or soft tissue infection or sepsis requires a bone biopsy before antibiotics are administered.