Keys To The Diagnostic Workup For Patients With Diabetic Foot Infections

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

   Aragon-Sanchez and colleagues found that limb salvage with surgical procedures localized to the foot occurred more than 90 percent of the time in patients with a limb- or life-threatening infection and at least one palpable pedal pulse.12 If monophasic signals are audible, obtain a vascular consultation. If necessary, one should administer appropriate antibiotics and maintain a clean and dry wound until vascular intervention is complete.

Evaluating The Neurological And Musculoskeletal Systems

When a patient with diabetes presents with a diabetic foot infection secondary to a foot ulcer, one can assume the patient has some component of peripheral neuropathy.

   A simple test to assess for peripheral neuropathy is the Ipswich Touch Test.13 To perform this test, the physician lightly touches or rests the tip of the index finger on the dorsum of the hallux and the tips of the first, third and fifth toes. Research has found the Ipswich Touch Test to have a 76 percent sensitivity, 90 percent specificity, a positive predictive value of 89 and negative predictive value of 77 in comparison to a vibratory threshold of ≥ 25 mV and 10-g monofilament testing at six sites on the foot for accurate diagnosis of peripheral neuropathy.13 The study also found the test to have significant interoperator reproducibility.

   The musculoskeletal examination should focus on the area from the knee to the toes. One should document a rapid assessment of muscle strength and any present deformities, including reducibility or rigidity of the deformities. Physicians can perform a more thorough musculoskeletal examination once there has been adequate treatment of the infection as this may include some level of amputation of the foot to garner control.

What The Research Shows On Wound Depth, Osteomyelitis And Other Dermatological Findings

Dermatological examination of the patient should first begin with exposure of both lower extremities from the knee to the toes. Cleanse the extremities with an antimicrobial cleanser as proper skin assessment cannot occur on skin of poor hygiene. One should take longitudinal and depth measurement of all ulcerations, including any undermining of the skin. Research has shown that wounds larger than 2 cm2 and deeper than 3 mm are associated with underlying osteomyelitis, increasing the risk of amputation.1,3,5,10 Assess wound depth by inserting a sterile cotton tip applicator, measuring stick or metal probe to the depths of the wound until you feel an endpoint.

   The landmark study by Grayson and colleagues reported that the ability to probe to bone at the base of the wound was a clinical sign of underlying osteomyelitis.14 Other authors subsequently criticized this study, noting that Grayson and colleagues performed it in patients who were hospitalized for severe diabetic foot infections and had a high pre-test prevalence of osteomyelitis.15-17

   Lavery and co-workers found that the negative predictive value of the probe to bone test was of greater clinical significance in the outpatient setting, ruling out osteomyelitis in wounds that did not probe to bone.17 However, they did agree that the ability to probe to bone in patients with severe diabetic foot infections, who have a high pretest probability of osteomyelitis, was a quick and effective means in aiding in the diagnosis.

   Assess the periwound skin for crepitus, induration and the extent of erythema. Crepitus is a late finding on physical exam. This finding should expedite transfer to the operating room for immediate surgical intervention. Assess erythema surrounding the ulcer using the erythema elevation test. This test differentiates between erythema secondary to inflammation, peripheral arterial disease and infection.

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