 | | Diabetic Foot Infections | | | Counselor, Foot infections are the most common problems in persons with diabetes. These individuals are predisposed to foot infections because of a compromised vascular supply secondary to diabetes. Local trauma and/or pressure (often in association with lack of sensation because of neuropathy), in addition to microvascular disease, may result in a variety of diabetic foot infections. The spectrum of foot infections in diabetes ranges from simple superficial cellulitis to chronic osteomyelitis. Infections in patients with diabetes are difficult to treat because these patients have impaired microvascular circulation, which limits the access of phagocytic cells to the infected area and results in a poor concentration of antibiotics in the infected tissues. For this reason, cellulitis is the most easily treatable and reversible form of foot infections in patients with diabetes. Deep skin and soft tissue infections also usually are curable, but they can be life threatening and result in substantial long-term morbidity. We value all your comments, so, if you have a suggestion for a newsletter subject but haven't submitted it yet, or if you have already submitted one but think of another, please take a minute to let us know by clicking on your "Reply" button and dropping us a note. To learn more about AMFS, Inc., the organization run by Physicians and Attorneys that provides medical experts and case review services nationwide, and has produced the following informational newsletter to aid you in understanding complex medical issues, please click here - www.amfs.com.
| | |  | Pathophysiology: Diabetes mellitus is a disorder that primarily affects the microvascular circulation. In the extremities, microvascular disease limits the blood supply to the superficial and deep structures. Pressure due to ill-fitting shoes or trauma further compromises the local blood supply at the microvascular level, predisposing the patient to infection. The infection may involve the skin, soft tissues, bone, or all of these tissues. Diabetes also accelerates macrovascular disease, which is evident clinically as accelerating atherosclerosis and/or peripheral vascular disease. Most diabetic foot infections occur in the setting of good dorsalis pedis pulses; this finding indicates that the primary problem in diabetic foot infections is microvascular compromise. Impaired microvascular circulation hinders white cell migration into the area of infection and limits the ability of antibiotics to reach the site of infection in an effective concentration. Diabetic neuropathy may be encountered in conjunction with vasculopathy. This may allow for incidental trauma that goes unrecognized (e.g.: blistering, penetrating foreign body). In chronic osteomyelitis bone fragments that are isolated have no blood supply. Administered antibiotics do not penetrate the devascularized infected bone fragments; they can enter the area of osteomyelitis only via the remaining blood supply. Therefore, antibiotic therapy alone cannot cure patients with chronic osteomyelitis without surgical debridement to remove these isolated infected elements. Surgical debridement is essential to remove the infected bony fragments that the antibiotics cannot reach so that affected areas can be treated with antimicrobial therapy.
| | | | | | History/Physical: Patients may or may not have a history of trauma or previous infection. Typical findings on physical exam include cellulitis and lymphangitis. Lymphangitis suggests a group A streptococcal etiology. If bullae are present, Staphylococcus aureus is the most likely pathogen, but group A streptococci occasionally may cause bullous lesions. Patients with deep skin and soft tissue infections may be acutely ill, with painful induration of the soft tissues in the extremity. Extreme pain and tenderness indicate the possibility of a compartment syndrome, which may be diagnosed with the aid of a CT scan. Similarly, extreme pain may be an indication of infection with clostridial species (i.e.: gas gangrene). With acute osteomyelitis unless peripheral neuropathy is present, the patient has pain at the site of the involved bone. Usually, fever and regional adenopathy are absent. In chronic osteomyelitis, the patient's temperature usually is less than 102°F. Discharge is not uncommonly foul. No lymphangitis is observed. Pain may or may not be present, depending on the degree of peripheral neuropathy.
| | | | | | Causes: The microbiologic features of diabetic foot infections vary according to the tissue infected. In patients with diabetes, superficial skin infections such as cellulitis are caused by the same organisms as those in healthy hosts, namely group A streptococci and S aureus. However, in unusual epidemiologic circumstances, organisms such as Pasteurella multocida (e.g.: from dog or cat bites or scratches) may be noted and should always be considered. In patients with diabetes, deep soft tissue infections can be associated with gas-producing gram-negative bacilli. Clinically, these infections appear as necrotizing fasciitis, compartment syndrome, or myositis. Gas gangrene is uncommon in persons with diabetes. Acute osteomyelitis usually occurs as a result of foot trauma in an individual with diabetes. The distribution of organisms is the same as in an individual without diabetes who has acute osteomyelitis. In chronic osteomyelitis, the pathogens are group A and group B streptococci, aerobic gram-negative bacilli, and Bacteroides fragilis, among others. Pseudomonas aeruginosa generally is not a pathogen in chronic osteomyelitis in patients with diabetes. When it is cultured, it is usually just a superficial colonizer and not a cause of the bone infection. On the other hand, B fragilis is an important bone pathogen in chronic osteomyelitis in patients with diabetes. Other pathogens implicated in chronic osteomyelitis in patients with diabetes include Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae.
| | | | | | Lab Studies: With cellulitis, the CBC count and erythrocyte sedimentation rate (ESR) are slightly or moderately elevated in cellulitis. Elevations are not diagnostic and, therefore, are unhelpful. Blood culture results usually are negative. If positive, they usually indicate the presence of group A or group B streptococci. Cultures of skin via aspiration or biopsy generally are unrewarding. With acute osteomyelitis, the CBC count usually reveals a leukocytosis, and the ESR is moderately or highly elevated. Blood culture results usually are negative. When positive, the findings most frequently indicate the presence of S aureus. With chronic osteomyelitis, the CBC count often is within the reference range. Usually, the ESR is very highly elevated; it may exceed 100 mm/h. The platelet count often is elevated in chronic osteomyelitis. Blood culture results usually are negative in patients with chronic osteomyelitis.
| | | | | | Imaging Studies: With cellulitis, imaging studies are not applicable. In patients with deep skin and soft tissue infections plain radiography, CT scan, or MRI may be performed to rule out a compartment syndrome and to demonstrate the presence of gas or a foreign body in the deep tissues. In acute osteomyelitis plain radiographic findings of bones generally become abnormal after 10-14 days. Soft tissue swelling and periosteal elevation are the earliest signs of acute osteomyelitis on a plain radiograph. Bone scan findings are positive within 24 hours in acute osteomyelitis. A bone scan is preferred to gallium or indium scans in the assessment of acute osteomyelitis. In chronic osteomyelitis plain radiographic findings invariably are abnormal. Bone scans usually are unnecessary unless diagnostic confusion exists with another disorder. A bone tumor is best differentiated from chronic osteomyelitis with the aid of bone scanning or MRI prior to definitive bone biopsy.
| | | | |  | Treatment: Antibiotics and surgical debridement are the mainstays of treatment. Antibiotics should be tailored to the organism. Surgical debridement in chronic osteomyelitis is the single- most important therapeutic intervention. Chronic osteomyelitis cannot be cured without adequate surgical debridement. In some cases, amputation may be required. If amputation is performed, physical therapy and rehabilitation may be started on an inpatient basis and completed on an outpatient basis.
| | | | | | Complications/Prognosis: Bacteremia may accompany cellulitis, skin or soft tissue infections, and/or acute osteomyelitis, but these are not complications per se. If chronic osteomyelitis is left untreated for years, it may lead to complications such as amyloidosis or squamous cell carcinoma at the site of drainage through the skin. Bacteremia and septic shock rarely, if ever, occur as a result of chronic osteomyelitis. The prognosis for cases of cellulitis, skin and/or soft tissue infections, or acute osteomyelitis depends on the adequacy of antimicrobial therapy and surgical debridement as indicated. For cases of chronic osteomyelitis, the prognosis is directly related to the vascular supply in the affected limb and the adequacy of surgical debridement.
| | | | | | Medical/Legal Pitfalls: Early recognition of a developing infection is directly correlated with a favorable outcome. The longer treatment is delayed the more tissue destruction will occur, and the more difficult the infection will be to treat. Delayed treatment will inevitably cause harm and disability to the patient and is a major cause of litigation. In general, diabetics with foot infections should be treated aggressively, often requiring admission and consultation with surgeons and infectious disease consultants. It is always best to treatment rapidly and comprehensively to avoid these complications. Patients with chronic osteomyelitis should be advised that if the infection is not adequately treated with sufficient surgical debridement and/or amputation, systemic complications may occur over time. Possible systemic complications include bacteremia and/or systemic infection, amyloidosis, and squamous cell carcinoma at the affected site.
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