Q: What are the signs and symptoms of a severely infected diabetic foot ulcer?
A:_______________________________________________________________
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Referral to plastic surgeon
When M.N. returns to the clinic with worsening drainage, edema, and spreading erythema, the decision is made to admit him to the hospital, start intravenous ampicillin/sulbactam (Unasyn) and ciprofloxacin (Cipro), and consult with a plastic surgeon.
Following the examination and review of the bone scan results, which show osteomyelitis, the surgeon recommends surgical therapy of the affected toe. He advocates aggressive debridement, and also thinks that this wound could require a staged surgical approach or amputation.
Q: Are there other laboratory or imaging studies you would like to obtain?
A:_______________________________________________________________
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Further primary care evaluation
Laboratory:
- Complete blood count, normal
- Erythrocyte sedimentation rate (ESR), 38
- C-reactive protein (CRP), 2.1
- Lipid panel: HDL 32 mg/dL, LDL 96 mg/dL, triglycerides 116 mg/dL
- Hemoglobin A1c, 6.0
Details of foot ulcers
Statistics
About 50% to 60% of serious foot infections are complicated by osteomyelitis, and 10% to 20% of mild to moderate infections likely involve the bone. Twenty-five percent of foot infections in persons with diabetes will spread to subcutaneous tissues or bone. Up to 50% of those with a foot infection will experience a recurrence within a few years.2 Approximately 10% to 30% with a diabetic foot ulcer will eventually require amputation. Infected foot ulcers precede 60% of amputations. Two thirds of patients with a diabetic foot ulcer have peripheral vascular disease, and 80% have lost protective sensation. Infections most commonly involve the forefoot, usually plantar surface.2
Pathophysiology
Ulcers develop from breaks in the dermal barrier with subsequent erosion of subcutaneous tissue. Healing is inhibited when wound-repair mechanisms are corrupted by impaired perfusion, infection, or repeated trauma. Ulceration progresses due to impaired arterial supply, neuropathy, or musculoskeletal deformities.1
Risk of ulceration correlates with number of risk factors. The risk is increased by 1.7 in persons with isolated peripheral neuropathy (TABLE 1), by 12 in those with neuropathy and foot deformity, and by 36 in those with peripheral neuropathy, deformity, and previous amputation.1
Pathology usually mixed. The feet have sensory and motor neuropathies that cause the patient to put abnormal stresses on them, resulting in trauma that may lead to infection. Immunologic impairment due to hyperglycemia also plays a role; this can include reduced function of neutrophils, monocytes, and complement. Skin and nail disorders are more common among persons with diabetes than in the general population, and these may also increase the rate of infection.2
TABLE 1
Risk factors predisposing to foot ulcers and inhibiting healing
| Vascular: arterial insufficiency or venous hypertension |
| Neurologic: sensory, motor, or autonomic neuropathy |
| Anatomical: altered biomechanics, limited joint mobility, bony deformity |
| Infections |
| Trauma |
| Diabetes |
Q: What are the patient’s choices for management of his ulcer and osteomyelitis?
A:_______________________________________________________________
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Management of ulcers
Optimal management should involve a multidisciplinary group of consultants. Mechanical debridement, systemic antibiotic therapy, and measures to reduce weight bearing are the main elements of effective care. Foot soaks and whirlpool therapy may be detrimental and lead to further skin breakdown, but moist dressings on granulating wounds may help.
Debridement a must. Remove nonviable, infected tissue to achieve a border of healthy, bleeding soft tissue and uninfected bone. Debridement improves the outcome of foot ulcers.3
When hospitalization is indicated. Determine whether or not the patient requires hospitalization based on the presence of a severe infection (TABLE 2) and need for surgical intervention, fluid resuscitation, IV antibiotics, or control of metabolic derangements.2 Consider hospitalization also if there is concern about the patient’s ability or willingness to comply with wound care, antibiotic therapy, or off-loading of the affected area.
Consider need for off-loading. Most diabetic wounds develop because of unperceived trauma, and likely do not heal because of ongoing trauma. Total contact casting, whereby loading levels to a foot ulcer are drastically reduced, has been shown to be effective in healing ulcers in about 6 weeks.4 This suggests that healing of neuropathic ulcers must include mechanical off-loading of the ulcer. Total contact casting has several limitations, and new modalities are being investigated.5
Obtain cultures. Wound culture results can greatly assist in determining appropriate antimicrobials. Gram stain can help direct therapy, and culture results are consistent with Gram staining in 95% of cases. Gram-stained smear is 70% sensitive for identifying organisms that grow on culture, and is much better for gram-positive organisms than for gram-negative bacilli.
Deep tissue specimens collected aseptically at surgery contain the true pathogens more often than more superficial samples. Curettage, involving tissue scraping with a scalpel from the base of a debrided ulcer, is more accurate than a wound swab. Wound swabs are likely to miss key pathogens as well as include nonpathogenic bacteria that confuse the antibiotic choice.2