Some 23.6 million diabetics currently live in the United States, and the diabetic foot is among the most serious and common long-term complication of diabetes. It accounts for more than 70,000 non-traumatic amputations annually, a rate 10 times higher than for nondiabetics. (www.diabetes.org/diabetes-statistics.jsp) In fact, 30 percent of diabetics over 40 have impaired sensation in their feet, and up to one-quarter will develop an infected diabetic foot ulcer during their lifetimes. (JAMA 2005;293:217.)
Diabetic foot ulcers are the most common indication for nontraumatic foot amputations in this population (Diabetes Metab Res Rev 2000;16[Suppl 1]: S1), and are a major cause of physical and psychological morbidity in patients with diabetes. While it may not be pretty to examine the diabetic foot, proper management is critical to help avoid amputation in these patients.
The Diabetic Foot
Although we often refer to the diabetic foot as a specific entity, the term actually refers to a diverse group of diagnoses including neuropathic ulcers, Charcot's neuroarthropathy, peripheral vascular disease, skin and soft tissue infections, and osteomyelitis. Diabetic neuropathy is the most significant risk factor for the development of the diabetic foot. Other predisposing factors include poor gylcemic control, trauma, ill-fitting footwear, old age, smoking, low socioeconomic status, and psychological factors. (QJM 2008;101:685.)
On exam, it is essential to determine whether the neuropathy is accompanied by an intact circulation, chronic ischemia, or critical ischemia that requires urgent attention. Up to two-thirds of patients with diabetic foot ulcers will have concomitant peripheral vascular disease making measurement of the ankle-brachial index (ABI) a necessary component of the exam. (J Fam Prac 2005;54:768.) To help risk-stratify patients, several screening tools have been developed, such as the guidelines by the International Working Group on the Diabetic Foot (Diabetes Care 2001;24:1442) or the Texas Foot Risk Classification. (Diabetes Care 2008;31:154.)
It is important to note that complications of diabetic foot often have an insidious onset with the patient blissfully oblivious to the nature of the problem, depending on the extent and severity of the neuropathy. Without a specific, detailed examination of the foot, significant findings such as acute ischemia, necrosis, or gangrene may be easily overlooked by the treating physician.
Charcot's neuroarthropathy develops as a result of abnormal mechanical stresses in the foot that would have been prevented by intact pain sensation. It is characterized by bone fragmentation, joint subluxation, and re-modeling in an insensate but well vascularized foot. Acute Charcot's foot presents with pain, warmth, and swelling in a neuropathic foot and can be easily mistaken for cellulitis, osteomyelitis, gout, or another inflammatory arthrophathy.
It is most commonly found in the mid-foot at the fifth tarsal-metatarsal joint (known as Charcot's joint), but may also be seen at the ankle, other tarsal-metatarsal joints, or at the metatarsophalangeal joints. In a patient with chronic Charcot's foot, the bony deformity persists, but the warmth, redness, and pain are absent.
A diabetic foot ulcer is defined as any full thickness skin breakdown on the foot of a person with diabetes, regardless of the time frame that the lesion has been known to exist. (MMWR 2003;52:1098.) Diabetes is not a primary cause of ulceration, but it leads to ulceration through a combination of impaired pain sensation, circulatory problems, poor wound healing, and other chronic skin changes. Lesions tend to be painless and located in areas of highest pressure or repetitive trauma on the heel, pad of the foot, or top of the toes.
When examining an ulcer, it is important to assess the location, size, and depth of the wound, the severity of the neuropathy, and whether there are any signs of infection or ischemia. (Plast Reconstr Surg 2006;117[7 Suppl]:193S.) Several grading systems, such as the International Working Group on the Diabetic Foot's PEDIS system (perfusion, extent [size], depth [amount of tissue loss], infection, and sensation) assist in classification, risk stratification, and research. (Diabet Metab Res Rev 2004;20[Suppl 1]:S90; also at www.iwgdf.org.) Keep in mind that many ulcers are covered with a fibrinous cap that may need to be debrided prior to an accurate assessment. Unfortunately, even properly treated ulcers tend to reoccur.
In addition to the typical signs and symptoms of infection, other indications of infection in the diabetic foot include purulent secretions, foul odor, necrotic tissue, the presence of maggots, and the failure of a properly treated wound to heal. (Plast Reconstr Surg 2006;117[7 Suppl]:193S.) Approximately one-quarter of foot infections in diabetics also involve the bone, and plain films should be routinely performed to evaluate for osteomyelitis and to exclude the presence of foreign bodies, soft-tissue gas, and occult fractures.
Additional imaging such as a bone scan, computed tomography, or magnetic resonance imaging also may be indicated. Diabetic foot infections are typically polymicrobial with aerobic Gram-positive, Gram-negative, and anaerobic organisms all commonly present. Cultures may be helpful to identify the causative organisms. Because all open wounds become colonized with skin flora, any cultures should be taken from deep-tissue specimens rather than from surface skin swabs. Diabetic patients are also at increased risk of onychomycosis due to elevated blood sugar levels, poor circulation, and other factors.
Management and Treatment
Proper foot hygiene should be strongly encouraged in all diabetic patients; the importance of well-fitting shoes, twice-daily foot checks, proper nail clipping, clean dry socks, and regular podiatric care cannot be overemphasized. Glycemic control and local wound care including foot elevation, support stockings, and limitation of physical activities should also be discussed. Warm soaks and lotions are no longer routinely recommended. (Am J Health Syst Pharm 1995;52:1199.)
Due to the risk of amputation and other severe complications, it is important to maintain a low index of suspicion for infection. Patients with onychomycosis should be started on topical and/or oral antifungal agents because diseased nails are often a nidus for infection. Mild foot infections may be treated with oral clindamycin, amoxicillin-clavulanate, levofloxacin, or trimethoprim-sulfamethoxazole for one to two weeks on an outpatient basis if close follow up can be arranged. (J Fam Pract 2005;54:768.)
Patients with moderate to severe infections should be admitted for intravenous antibiotics, wound care, and surgical consultation. Broad-spectrum antibiotics such as ertapenem, piperacillin-tazobactam, or linezolid are all effective. Vancomycin should be also considered to cover for resistant Gram-positive organisms. Surgical consultation should be obtained for wound debridement and to assess for removal of the infected bone if osteomyelitis is present. Vascular evaluation also should be obtained if there is concern for underlying peripheral vascular disease or ischemia.
Although rarely initiated in the ED, nontraditional treatment options for the diabetic foot include hyperbaric oxygen and vacuum-assisted closure (VAC). Silver-based wound dressings also may be effective for refractory ulcers, although no randomized clinical trials have been conducted to date. (Cochrane Database Syst Rev 2006;(1):CD005082.) In a blast-from-the-past, larval therapy (Diabetes Care 2003;26:446) and topical honey. (J Fam Pract 2005;54:533.) also have been suggested as modern-day treatments for the diabetic foot.