From the Guidelines
The best initial imaging test for a diabetic patient with suspected foot infection and peripheral artery disease is plain radiography (X-ray). This recommendation is based on the most recent and highest quality study available, which suggests that plain radiographs should be obtained first as they are readily available, cost-effective, and can identify important findings such as bone destruction, gas in soft tissues, foreign bodies, and arterial calcifications 1. While X-rays have limited sensitivity for early osteomyelitis (only about 50-60% in the first 2 weeks), they provide a valuable baseline assessment.
Some key points to consider when evaluating a diabetic patient with a suspected foot infection include:
- The presence of a draining ulcer, edema, and erythema, which are all indicative of a potential infection
- The patient's medical history, including peripheral artery disease and uncontrolled type 2 diabetes with diabetic neuropathy, which can increase the risk of complications
- The importance of vascular assessment, which may require additional studies like ankle-brachial index measurement or vascular ultrasound
If the X-ray is negative but clinical suspicion for osteomyelitis remains high, more advanced imaging should follow, such as MRI, which has superior sensitivity (90-100%) for detecting early bone infection, soft tissue abnormalities, and can help distinguish between osteomyelitis and Charcot arthropathy 1. The combination of plain radiography followed by appropriate advanced imaging when necessary provides the most efficient diagnostic approach for these complex patients.
It's worth noting that the 2024 European Journal of Nuclear Medicine and Molecular Imaging study 1 provides more recent and higher quality evidence compared to the 2012 Clinical Infectious Diseases study 1, and therefore its recommendations should be prioritized.
In terms of specific imaging modalities, the study suggests that MRI is the modality of choice for the diagnosis of Charcot neuro-osteoarthropathy, and that WBC SPECT/CT is the most effective technique to differentiate OM from Charcot arthropathy 1. However, for the initial evaluation of a diabetic patient with suspected foot infection, plain radiography remains the best first step.
From the Research
Initial Imaging Test for Diabetic Foot Infection
The best initial imaging test for a diabetic patient with a suspected foot infection and peripheral artery disease is Magnetic Resonance Imaging (MRI).
- MRI has been shown to be a powerful, noninvasive tool for determining the presence or absence of osteomyelitis in the patient with a diabetic foot ulcer 2.
- It has high sensitivity for the detection of osteomyelitis in the diabetic foot, although it may have lower specificity related to Charcot neuropathic osteoarthropathy 3.
- MRI can provide a detailed and accurate depiction of the anatomy, which can facilitate surgical planning 4.
- It has been found to be more sensitive and accurate than plain radiographs and technetium and gallium scans in diagnosing osteomyelitis in diabetic foot infections 4.
Alternative Imaging Tests
While MRI is the preferred initial imaging test, other tests may be used in certain situations:
- Plain radiography should be the first step of examination if osteomyelitis is suspected, followed by three-phase bone scintigraphy or MRI 5.
- Computed Tomography (CT) or MRI may be used as a final imaging procedure if other tests are negative and there is high clinical suspicion of osteomyelitis 5.
- MR angiography may be used to evaluate the vascular status of the foot, but it may be limited by venous contamination in the infrapopliteal region 3.
Key Considerations
When choosing an initial imaging test for a diabetic patient with a suspected foot infection and peripheral artery disease, it is essential to consider the following: