From the Guidelines
No, an MRI of the foot is not necessary for every diabetic foot infection, but rather should be reserved for cases where the diagnosis of osteomyelitis remains in doubt despite clinical, plain X-rays, and laboratory findings. The diagnosis of diabetic foot infections can often be made clinically through physical examination and basic tests such as complete blood count, erythrocyte sedimentation rate, and C-reactive protein 1. According to the iwgdf/idsa guidelines, a combination of probe-to-bone test, plain X-rays, and ESR, or CRP, or PCT should be considered as the initial studies to diagnose osteomyelitis of the foot 1.
Initial Evaluation
For most uncomplicated diabetic foot infections, the initial evaluation should include:
- Physical examination to look for signs of infection (redness, warmth, swelling, pain, purulent discharge)
- Basic tests like complete blood count, erythrocyte sedimentation rate, and C-reactive protein
- Plain X-rays as the initial imaging study to rule out gas in tissues, foreign bodies, or obvious bone involvement
Role of MRI
MRI should be considered when:
- The diagnosis of osteomyelitis remains in doubt despite clinical, plain X-rays, and laboratory findings 1
- There is a suspicion of deep or complex infections
- The extent of infection is unclear after initial evaluation
- Osteomyelitis is suspected, especially with exposed bone, ulcers larger than 2cm², or ulcers present for more than 1-2 weeks
Additional Imaging Modalities
Other imaging modalities such as positron emission tomography (PET), leucocyte scintigraphy, or single photon emission computed tomography (SPECT) can be considered as alternatives to MRI for the diagnosis of diabetes-related osteomyelitis of the foot 1. However, the choice of imaging modality should be based on the specific clinical scenario and the availability of resources.
Clinical Judgment
Ultimately, the decision to order an MRI or other imaging modalities should be based on clinical judgment and the individual patient's needs. The goal is to provide the best possible care while minimizing unnecessary tests and procedures. As stated in the diagnostic imaging of the diabetic foot guidelines, advanced imaging with MRI and WBC scintigraphy, or [18F]FDG PET/CT, should be considered when it is needed to better evaluate the location, extent or severity of the infection, in order to plan more tailored treatment 1.
From the Research
Diabetic Foot Infection Diagnosis
- The diagnosis of diabetic foot infections is crucial for effective treatment and management, and various imaging modalities can be used to aid in diagnosis 2.
- Clinical signs and symptoms, as well as serum inflammatory markers, can be supportive but not diagnostic of soft tissue infection 2.
- Imaging examinations, including plain X-ray and advanced methods like magnetic resonance imaging (MRI) and nuclear imaging, can help in cases where the diagnosis or localization of infection is uncertain 2.
Role of MRI in Diabetic Foot Infection Diagnosis
- MRI can be a valuable adjunct in the evaluation of the diabetic foot, providing accurate information regarding the presence and extent of infection 3.
- MRI has been recognized as the most accurate imaging modality for the detection of diabetic foot osteomyelitis, but its accuracy may be affected by the presence of ischemia 4.
- In some cases, MRI-only episodes did not differ epidemiologically from other diabetic foot osteomyelitis cases and did not influence the choice of therapy or remission rate 5.
Limitations and Considerations
- The certainty of evidence statements regarding the diagnosis of diabetic foot infections is often low due to the weak methodology of many studies 2.
- The use of MRI for the diagnosis of diabetic foot osteomyelitis may not be necessary in all cases, and plain X-ray remains the first-line imaging examination 2, 5.
- The cost and availability of MRI may also be considerations in its use for diabetic foot infection diagnosis 5.