Diabetic Foot Ulcers

Foot and lower extremity ulcers and associated infections are a major source of morbidity in the diabetic population, affecting some 15 percent of diabetics during their lifetime and accounting for 20 percent of diabetic admissions and nearly 50 percent of all lower extremity amputations in the United States. Direct costs each year for diabetic lower extremity ulcers and their complications exceed 500 million dollars annually. A pathologic triad of neuropathy, premature atherosclerotic vascular disease, and impaired immunity combine to make diabetic foot ulcers a multidisciplinary treatment challenge.

Peripheral neuropathy predisposes diabetic feet to ulceration, infection, and joint degeneration (Charcot joints) through the mechanisms of lack of sensation, diminished or absent proprioception, anhidrosis, and poor circulatory and thermal regulation. Risk factors for foot and lower extremity ulcers include high HgbA 1c levels, older age, longer duration of diabetes, foot deformities, smoking, retinopathy, peripheral neuropathy, albuminuria, and low diastolic blood pressure. Preventing foot ulcers involves education on foot care and proper fitting of footwear, combined with good glycemic control to limit development of neuropathy and premature vascular disease.

A thorough clinical examination of the diabetic patient's feet should be performed during all emergency department visits even for unrelated complaints. Hair and nail growth, calluses, corns, deformities, erythema, swelling, sensation, and vascular function should be assessed. Any ulcerations found should be unroofed surgically and probed using a blunt-ended rigid probe to determine the depth and possible bone, joint, or tendon involvement. The ability to probe to bone through the ulcer suggests the strong possibility of osteomyelitis and deep space soft tissue infection.

Based on the initial patient evaluation and foot examination, foot ulcers can be classified into non-limb-threatening, limb-threatening, and life-threatening infections. Non-limb-threatening infection is defined as small (under 2 cm of cellulitis or inflammation), does not involve deep structures or bone, and is the result of recent injury to a well-perfused limb. Limb-threatening infection (more than 2 cm of cellulitis or inflammation) with associated ascending lymphangitis, deep ulceration or abscess, large area of necrotic tissue, involvement of deep structures or bone, gangrene, or critical lower extremity ischemia defined by absence of palpable pulses. Life-threatening infection has clinical signs of sepsis, including fever, leukocytosis, hypotension, tachycardia, tachypnea, altered mental status, and metabolic abnormalities ranging from hypoglycemia to DKA and HHNS.

Generally, it is suggested that the debridement of foot and leg ulcers be just sufficient to judge the depth and extent of the ulcer and to rule out deep abscess. Management of foot ulcers that do not appear infected and do not expand to the deep structures or bone on exploration should include topical antibiotics and nonadherent padded dressings. Follow-up referral with a specialist in diabetic foot care should occur within a few days. Constrictive dressings, such as Unna paste boot (alkaline methylene blue), and tight-fitting shoes should be avoided. Avoidance of weight bearing on the affected limb is critical to avoid progression to infection and for proper healing.

Radiographs of the foot are indicated to exclude subcutaneous gas, foreign bodies, osteomyelitis, and Charcot joints. Swab cultures of foot ulcers may provide misleading results. Culture of tissue excised from the base of the ulcer provides the most accurate identification of the bacteria involved. Commonly isolated organisms include Bacteroides species, Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus, Escherichia coli, Proteus mirabilis, and Pseudomonas aeruginosa. Empiric antibiotic therapy should be directed against these organisms.

In choosing antibiotic therapy for these infections, severity should be taken into account (Iabje.,2Q.9-7). The use of aminoglycosides should generally be avoided because of their associated nephrotoxicity. For limb-threatening and life-threatening infections, immediate surgical consultation is indicated for incision and debridement, possible revascularization, or amputation.

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