The Diabetic Foot—Imaging Options and Considerations
Patients with diabetes may present with an array of foot disorders that include, but are not limited to, neuropathy, ulceration, and osteomyelitis. Ischemia and infection are common clinical concerns as either, or both, may be involved in the pathogenesis of these disorders. Management choices can be difficult to make and diagnostic imaging is often sought to help clarify the clinical picture. The imaging options available all have strengths and weaknesses in terms of their clinical relevance. A common problem encountered with imaging is distinguishing inflammation that is due to trauma—e.g. surgical, mechanical or Charcot arthropathy—from soft-tissue or osseous infection. This article reviews the most common imaging options available to clinicians and summarizes the benefits and drawbacks of each. No single imaging modality can answer all the clinical questions that arise in the setting of the diabetic foot, but knowing the features of the imaging choices available to you may help answer the most pressing questions.
Pathogenesis of Ischemia and Infection
While foot ulcers are the most common complication in the diabetic foot, infections rank a close second.1 Sensory neuropathy in the distal regions of the extremities predisposes many diabetics to traumatic insults that can lead to skin breakdown, ulceration, and infection. Impaired perfusion due to peripheral vascular disease and microvascular abnormalities reduces the patient’s capacity to heal wounds and recover from infection.2 In the diabetic foot, infected skin ulcers, the development of cellulitis, osteomyelitis, and abscess are major sources of morbidity.
The management of patients with diabetic foot disorders can vary substantially depending on the presence and extent of infection, necrosis, and osteomyelitis.3 Imaging of the diabetic foot may provide information that can aid the clinician in making patient management decisions. Diagnostic imaging procedures may also provide information that helps guide surgical planning.
This basic modality may be indicated when bone involvement is suspected. Radiographs can detect cortical fragmentation, osteomyelitis, fractures, arterial calcifications, and soft-tissue gas and articular deformities, including Charcot osteoarthropathy (see Figure 1).1,4 While radiography is often used initially, an early diagnosis of osteomyelitis may be difficult to make as changes on radiographs are often subtle, or absent, in the early stages of the disease process.5 Thus, this imaging modality is useful for detecting changes associated with the later stages of osseous infection (typically two or more weeks from onset) (see Figure 2).6 This limitation is partly responsible for the modality having low sensitivity in the detection of osteomyelitis. While studies show radiographs typically have a higher specificity than sensitivity, periosteal reaction and post-traumatic changes can be non-specific. For example, the appearance of Charcot osteoarthropathy can be mistakenly identified as osteomyelitis on radiographs.6
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