What is the best approach to diagnose foot osteomyelitis in a diabetic patient who cannot undergo a Magnetic Resonance Imaging (MRI) scan?

From the Guidelines

The best approach to diagnose foot osteomyelitis in a diabetic patient who cannot undergo MRI is to use a combination of the probe-to-bone test, plain X-rays, and laboratory tests such as ESR, CRP, or PCT as the initial studies. This approach is based on the most recent guidelines from the International Working Group on the Diabetic Foot (IWGDF) and the Infectious Diseases Society of America (IDSA) 1. The initial evaluation should include a thorough clinical examination looking for signs of infection such as erythema, warmth, swelling, and exposed bone. Key points to consider in the diagnosis include:

• The probe-to-bone test can be useful, especially in patients at high risk for osteomyelitis, as a positive test is largely diagnostic 1.
• Markedly elevated serum inflammatory markers, especially erythrocyte sedimentation rate (ESR), are suggestive of osteomyelitis in suspected cases 1.
• Plain X-rays should be obtained, although they may be negative in early infection.
• If the diagnosis remains in doubt, alternative imaging modalities such as positron emission tomography (PET), leucocyte scintigraphy, or single photon emission computed tomography (SPECT) can be considered 1.
• Bone biopsy with histopathological examination and culture remains the gold standard when imaging is inconclusive, providing both a definitive diagnosis and information on causative organisms to guide antibiotic therapy. This multimodal approach compensates for the lack of MRI access while still providing accurate diagnostic information, prioritizing the reduction of morbidity, mortality, and improvement of quality of life for the patient.

From the Research

Diagnosis of Foot Osteomyelitis in Diabetic Patients Without MRI

In diabetic patients who cannot undergo a Magnetic Resonance Imaging (MRI) scan, diagnosing foot osteomyelitis poses a significant challenge. Several alternative imaging techniques can be employed to aid in the diagnosis.

Available Imaging Techniques

• Plain Radiography: While plain radiographs can be specific, they often lack sensitivity in detecting early changes of osteomyelitis 2, 3.
• Technetium-99m Bone Scintigraphy: This method is sensitive but has a high false-positive rate, making it less specific 4, 5, 2.
• Indium-111-Labeled Leukocyte Scintigraphy: This technique has been shown to be both sensitive and specific for diagnosing osteomyelitis in diabetic patients, especially when MRI is not available 6, 3.
• Technetium-99m Human Immune Globulin (HIG) and Technetium-99m-Labeled White Blood Cell Scintigraphy: These methods have also been evaluated for their utility in diagnosing osteomyelitis, with the combination of four-phase bone scintigraphy and white blood cell scans showing high accuracy 5.

Diagnostic Approach

Given the limitations and advantages of each imaging technique, a stepwise approach can be considered:

• Initial Evaluation: Plain radiography can be used as an initial screening tool due to its wide availability and low cost 4, 2.
• Follow-Up: If plain radiographs are inconclusive, technetium-99m bone scintigraphy or indium-111-labeled leukocyte scintigraphy can be used as a next step 6, 4.
• Specificity and Sensitivity: For higher specificity and sensitivity, especially in cases where neuroarthropathy or soft-tissue ulcers are present, indium-111-labeled leukocyte scintigraphy or the combination of four-phase bone scintigraphy with white blood cell scans may be preferred 6, 5.

Considerations

It is crucial to interpret the results of these imaging studies in the context of clinical findings and, when possible, to correlate them with surgical or histological confirmation 6, 5, 2, 3. Each patient's condition, including the presence of neuroarthropathy, vascular insufficiency, or ongoing antibiotic treatment, should be considered when selecting the most appropriate diagnostic approach 6, 4, 5.