The authors of this month's continuing education article present a thorough and homogeneous foot examination paradigm that is comprehensive, standardized, reliable, validated (albeit operator dependent), and easy to learn. Because we care for a complex patient population, often presenting with a constellation of signs and symptoms and diagnoses, we must systematize our evaluations correspondingly. The pattern of comorbid disease manifestations related to the foot as a harbinger of diabetic complications includes peripheral (sensory motor) neuropathy, vasculitis, microvascular disease, venous hypertension, peripheral arterial disease, and diabetes.1-3 Therefore, a set of assessment tools that brings everything together linked to evidence-based practice would be ideal.
In addition to the selection of a diagnostic test, wound care practitioners must grapple with issues of sensitivity,4 specificity, and accuracy of diagnostic examinations. For example, a positive radiograph for Charcot foot is very specific; however, it is not sensitive.4,5 On the other hand, a more highly sensitive test may reveal the condition much earlier but will be negative if the patient does not have the disease. For example, a triple-phase bone scan may show increased activity, but it is highly sensitive to other acute nonspecific inflammatory conditions as well, and not specific to a Charcot joint.4,5 In contrast, magnetic resonance imaging of the foot in Charcot is extremely sensitive, with 100% detection of abnormalities; it also has a specificity rate of 80% for osteomyelitis and has good negative predictability when there are equivocal radiographs or bone scans.4-6
The diagnosis of diabetic peripheral neuropathy (DPN) is dependent on careful history and physical examination aided by practical diagnostic and screening tools.7-10 To illustrate this sensitivity versus the specificity paradigm, consider a Semmes-Weinstein monofilament examination (SWME) as a diagnostic test for DPN.8 The SWME has a sensitivity ranging from 57% to 93% and a specificity ranging from 75% to 100%. The most sensitive method using the SWME is to test the third and fifth metatarsal heads on each foot; a positive test is the inability of the patient to sense either site, resulting in a sensitivity of 93% with a 95% confidence interval.7,8 A quantitative analysis of 16 studies with sufficient data revealed that the SWME is both relatively sensitive and highly specific when compared with nerve conduction studies (NCS).8
Current literature on diagnosing DPN suggests that NCS are the criterion standard.8 These studies are used to identify patients with DPN because they are objective and sensitive. They also appear to be a reasonable surrogate marker for neuropathy.8 The Diabetes Control and Complications Trial Research Group has demonstrated that NCS can be used in large, multicenter clinical investigations of DPN. However, the clinical uses of NCS are limited because of expense and availability.8
Mnemonics are a useful tool to help remember the complicated concept of sensitivity and specificity in clinical practice. In a test that has sensitivity,: the mnemonic is SnOut (sensitive test rules out disease).4 If the test possesses specificity, the mnemonic is SpIn (specific test rules in disease).4 In the best-case scenario, providers would use 2 or 3 tests, triangulate results (combined sensitivity and specificity), and improve diagnostic accuracy.4
A common complication of diabetes, DPN has a protracted subclinical latency period in up to 50% of patients.2 However, recent literature has shown that DPN may be a presenting symptom, and a small percentage of patients may have overt neuropathy at the time of diabetes diagnosis. The exact pathogenesis remains unclear and may involve metabolic and vascular dysfunction.1-3 These aforementioned diagnostic modalities play an essential role in objectively identifying neuropathy in its earliest stages and potentially preventing extreme morbidity and healthcare costs, preserving function and quality of life.
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