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Most diabetic foot infections are caused by unrecognized
or mistreated ulcerations.
By Warren S. Joseph, DPM
Most of these infections are caused by foot ulcerations that are either not recognized in a timely fashion or inadequately treated. A coordinated approach is required to manage diabetic foot infections, preferably by a multidisciplinary team, including an infectious disease specialist, internist, vascular surgeon, podiatrist as well as a medical microbiologist. The IDSA guidelines were compiled to help reduce medical morbidity, psychological distress and financial costs associated with diabetic foot infections.
COORDINATED TEAM NEEDED
In the ISDA executive summary, my colleagues and I wrote that diabetic foot infections require attention to local and systemic issues by a coordinated team, as mentioned above. Foot ulceration is the major factor predisposing the diabetic foot to infections. This condition is usually associated with diabetic peripheral neuropathy, while peripheral vascular disease and immunological disturbances play secondary roles.
Contrary to earlier convention that all diabetic foot infections were a polymicrobial mix of gram-positive, gram-negative aerobic and anaerobic organisms, it is now recognized that Staphylococcus aureus and other aerobic gram-positive cocci are the primary pathogens in diabetic foot infections. However, gram-negative rods may be found in patients who have chronic wounds or who have recently received antibiotics. Patients who have foot ischemia or gangrene may have obligate anaerobic pathogens.
The diagnosis of these infections should be made on a clinical basis by observing local signs and symptoms of inflammation. There is limited usefulness for lab tests including wound cultures in infection diagnosis, with the exception of osteomyelitis cases.
Although the guidelines indicate that, if possible, specimens should be sent for culture prior to the initiation of empirical antibiotic therapy, such therapy should be directed primarily against the aerobic gram-positive organisms.
INFLAMMATION CAN MIMIC INFECTION
Not all patients with ulceration and surrounding inflammation will have infections. Charcot joint changes, superimposed gouty arthritis, inappropriate footwear and excessive weight bearing can cause inflammation and changes that mimic infection.
Imaging studies are useful for a better diagnosis or definition of deep, soft-tissue purulent collections. Imaging studies are regularly needed for the detection of pathological findings in bone. While plain radiography may be acceptable in many of the cases, MRI is more sensitive and specific for the detection of soft-tissue lesions.
The guidelines state that infections should be categorized according to severity, based on clinical and laboratory features. Most importantly are the extent and specific tissues involved, the adequacy of arterial perfusion and the presence of systemic toxicity or metabolic instability. Infection categorization enables a determination to be made regarding the risk to the patient and the limb, in turn dictating the urgency of treatment.
Current evidence does not support routine culturing or treating uninfected ulcers with antibiotics. It is necessary for virtually all infected wounds, however, but it must be coupled with appropriate wound care.
SELECT REGIMEN BASED ON SEVERITY
The guidelines direct caregivers to select an antibiotic regimen based on the severity of the infection and the likely etiology. Therapy aimed at aerobic gram-positive cocci might be enough for mild-to-moderate infections in patients who have not recently had antibiotic treatment. Broad-spectrum therapy, while not typically required, is indicated for severe infections. Recent antibiotic use and local antibiotic susceptibility data should be considered. Culture results and susceptibility data should form the basis of a definitive therapy. The presence of methicillin-resistant S. aureus (MRSA) is becoming an increasing problem in the diabetic foot infection and should be considered in communities with a large prevalence of these organisms or in patients at high-risk. These high-risk patients include those that have had previous MRSA infection, those that have been institutionalized or those who have been on multiple previous courses of antibiotics.
Only limited evidence exists for the choice among topical, oral and parenteral antibiotic agents. Almost all severe and many moderate infections require parenteral treatment, at least initially. The guidelines recommend the use of highly bioavailable oral antibiotics for most mild and some moderate infections and topical therapy for some mild, superficial infections.
TREAT UNTIL RESOLVED
Antibiotic treatment should continue until the infection has resolved – not necessarily until the wound has healed. A basic guideline would be 1 to 2 weeks for mild infections, with an additional 1 to 2 weeks if needed; 2 to 4 weeks for moderate infections and 4 to 6 weeks for osteomyelitis.
Clinically stable patients in whom infections do not clear up after one or more courses of therapy should be discontinued from all antimicrobials and cultured. Surgical consultations should be obtained for infections that are accompanied by a deep abscess, extensive bone or joint involvement, crepitus, substantial necrosis or gangrene or necrotizing fascitis. The guidelines committee said that evaluating the limb’s arterial supply and revascularizing when indicated are particularly important.
WOUND CARE NEEDED
Wound care – combined with antibiotics – is crucial for healing. This includes proper cleansing, debridement and off-loading pressure. A specific wound dressing or wound healing agent is not recommended, due to lack of sufficient evidence.
Patients should have early and careful observations. While studies have not clearly defined the role of adjunctive therapies for diabetic foot infections, some reviews suggest that granulocyte colony-stimulating factors and systemic hyperbaric oxygen therapy may help prevent amputations. These treatments may be indicated for severe or nonresponsive infections.
Osteomyelitis may be difficult to distinguish from noninfectious osteoarthropathy, therefore bone biopsy may be required, the guidelines note.
Attempts have been made to classify malperforans ulcerations, and while some systems have been in general usage, an accepted and validated system has not been adopted. Foot ulcerations in diabetic patients can have a wide spectrum of appearances and even with the best medical care any lesion can worsen rapidly.
CONCLUSIONS
The ultimate goal of diabetic foot infection treatment is to eradicate the infection and avoid soft tissue loss and subsequent amputations. A patient who has had an infection is likely to have more. It is important for clinicians to emphasize preventive strategies with patients. The best way to prevent foot infections is early detection of neuropathy. Patients should be told about the importance of optimal glycemic control, appropriate footwear, avoiding trauma, daily self-examination of the feet and reporting any changes to their physician.
Current research has uncovered much about the treatment of diabetic foot infections, however more research is needed. The committee especially recommends that adequately powered prospective studies be undertaken to elucidate and validate systems for classifying infection, diagnosing osteomyelitis, defining optimal antibiotic regimens in various situations and clarifying the role of surgery in treating osteomyelitis.
Warren S. Joseph, DPM, is from the section of podiatry, department of primary care, at the Veterans Affairs Medical Center, Coatesville, Pa. He can be reached at wsjoseph@comcast.net.
1. Lipsky BA, Berendt AR, Deery HG et al. ISDA guidelines: Diagnosis and treatment of diabetic foot infections. Clin Infect Dis. 2004;39:885-910.
2. Joseph WS, Tan JS. Infections in diabetic foot ulcerations. Current Infectious Disease Reports. 2003;5:391-397.
