When antibiotics are needed. In gross infections and cellulitis, topical antibiotics may reduce bacterial loads, but there are few published data about their efficacy in diabetic foot infections. The Wagner ulcer grading system (TABLE 3) is most widely used for tracking diabetic foot ulcers, but it does not allow for identification of superficial infection and has not been validated as an effective tool.6 An alternate method of classifying foot ulcers, taken from Lipsky et al, is shown in TABLE 4.
Currently systemic antibiotics are recommended only for established infection, although one study suggested that antibiotic therapy in clinically uninfected foot ulcers may significantly improve healing.7
Optimal duration of antibiotic therapy has not been studied, but convention has found 1 to 2 weeks to be effective for mild to moderate infections, at least 2 weeks for serious infections, and at least 6 weeks for osteomyelitis.2
Oral antibiotics are indicated when the ulcer is believed to be infected, and they should cover the usual pathogens, streptococci or staphylococci7 (TABLE 5). Treat severe infections with intravenous broad-spectrum antibiotics, covering for gramnegative and gram-positive aerobes and anaerobes.
Studies have shown similar therapeutic outcomes between high-dose oral fluoroquinolones and intravenous cephalosporin therapy. Oral fluoroquinolones cause fewer side effects and reduce hospitalizationrelated costs compared with cephalosporins, penicillinase-resistant penicillins, and vancomycin.8 Clindamycin or metronidazole may be added to fluoroquinolones to cover anaerobic organisms in severe or limb-threatening infections.9 One study found that patients treated with vancomycin had a greater rate of recurrence.5
Staphylococcus aureus is the most important pathogen in diabetic foot infections and may cause disease in isolation or as part of a mixed infection. Gram-negative rods, usually Enterobacteriaceae, are found in patients with chronic or previously treated infections. Pseudomonas species may be isolated from wounds that have been soaked or treated with wet dressings. Enterococci are more likely to be cultured from patients previously treated with a cephalosporin. Suspect anaerobes in cases of ischemic necrosis or deep tissue infections.2
When a person with diabetes has peripheral vascular disease, therapeutic antibiotic concentrations are often not achieved in infected tissues even with adequate serum levels.2 Novel methods of antibiotic delivery are being experimented with in an effort to solve this problem.
Surgery. Surgical options may include plastic reconstruction involving debridement and either primary closure or flap coverage. Optimally, vascular-bypass is performed to allow either primary healing or surgical reconstruction. If revascularization is not possible, amputation may be required.
If osteomyelitis complicates the picture. No validated or well-accepted guidelines exist for diagnosing or treating diabetic foot osteomyelitis. Factors that may suggest osteomyelitis: long-standing ulcers (>4 weeks), large (>2 cm) or deep ulcers (>3 mm), elevated ESR (>70 mm/h).2
Laboratory assays for diagnosing osteomyelitis can include measurements of erythrocyte sedimentation rate or C-reactive protein, though there are insufficient studies to assess their usefulness. One study found that 100% of patients with an ESR >70 mm/hr had osteomyelitis, despite lack of physical signs of inflammation. In diabetic patients with noninflamed foot ulcers, ESR can have a specificity of 100% and sensitivity of 28%. With inflamed ulcers, the sensitivity decreases to 23%.8 Some believe that the ESR can be used to follow osteomyelitis, and a persistent elevation or rise after initial fall would suggest osteomyelitis. Studies are inadequate to support this, however.5
Imaging for osteomyelitis can begin with plain films, which may show softtissue swelling, disruption of the bone cortex, and periosteal elevation. The American College of Radiology suggests this in the guidelines.10 However, 50% of the bone may be destroyed before these changes are evident. Plain films have a sensitivity of 28% to 100% and a specificity of 69% to 92%. If initial films yield normal results, it may be useful to repeat them in 2 to 4 weeks.9
MRI is highly sensitive (>90%) and specific (>80%), and may be even better with gadolinium. MRI is more sensitive for forefoot osteomyelitis than a leukocyte scan.11 Positron-emission tomography (PET) scans and high-resolution ultrasound may be helpful in the future.
Some studies suggest probing of sinuses and deep ulcers may be more sensitive than imaging. Palpable bone found at the base of an ulcer, with no overlying soft tissue, is highly predictive of osteomyelitis.1 Visible bone in a nontraumatic wound suggests osteomyelitis, with a sensitivity of 32% and specificity of 100%.12 The gold standard for diagnosis of osteomyelitis is obtaining a specimen of bone for pathology and culture.9