Keys To The Diagnostic Workup For Patients With Diabetic Foot Infections

Valerie L. Schade, DPM, AACFAS, and Nathan S. Higa, DPM, AACFAS

Delays in diagnosing diabetic foot infections can increase the risk of complications. Accordingly, these authors offer a closer look at pertinent principles in the diagnostic workup ranging from insights on the patient history and physical exam to key tips on laboratory studies and imaging studies.

Diabetes accounts for more than 60 percent of all non-traumatic amputations that occur in the United States every year.1 Diabetic foot infections are the primary cause of amputation in up to half of these cases.1 The majority of these infections are secondary to a foot ulcer with 10 to 60 percent being complicated by underlying osteomyelitis based on severity of infection ranging from mild to severe respectively.2-5

   The clinical appearance of a patient with a diabetic foot infection often does not correlate with the severity of infection.5-7,8 A delay in appropriate treatment of a moderate or severe diabetic foot infection increases both the risk and level of amputation.7 Proper workup of a patient presenting with a diabetic foot infection is paramount in establishing severity and initiating appropriate treatment.

   The initial part of an evaluation involves obtaining a thorough history from the patient. One should follow a standard format (i.e. history of present illness, past medical history, past surgical history, medications, allergies and tobacco/alcohol and illicit drug use). Questions should be specific in regard to the duration of diabetes; the duration of the ulcer if present; and any previous history of ulceration, infection and amputation.

   Research has shown that patients are at greater risk for severe infection if they have a diagnosis of diabetes for more than 10 years, prolonged duration of ulceration and a previous history of diabetes-related complications of the lower extremities.4,9,10 Document tobacco use as it is a primary contributing factor to the development of peripheral arterial disease, which is a major risk factor for lower extremity amputation in patients with diabetes.4,6

   The physical examination should occur in a methodical manner to ensure you do not miss any steps in proper clinical assessment of the patient. First assess the patient’s vital signs to ensure he or she is clinically stable prior to performing a focused examination of the lower extremity. Patients who are febrile and systemically labile have a severe infection, and should be admitted for prompt initiation of treatment.

   The difficulty comes in assessing patients with a diabetic foot infection as they often appear less toxic than the severity of their infection would indicate. Approximately 50 percent of patients are afebrile and without leukocytosis at presentation.5-7,8,11 This is where a thorough, focused examination of the lower extremity, laboratory studies and imaging tests are paramount in helping determine the severity of the infection.

Pertinent Pointers On The Vascular Examination

One should assess the vascular status of all patients with a Doppler. This will negate the potential of falsely palpating pulses in a foot with compromised vascularity. Assess the dorsalis pedis, posterior tibial and peroneal arteries. In addition, one should perform Doppler examination of the first interspace. This connection between the dorsal and plantar vascular supply can become critical in dictating the viability of amputation levels, especially in patients with compromised vascularity.

   Also assess the dorsal digital arteries in conditions localized to a digit. Upon hearing a biphasic or triphasic arterial signal, the physician can feel more confident that distal arterial flow is adequate for healing as these signals correlate with a palpable pulse, which may be difficult to assess in a swollen limb.

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