From the Guidelines
To rule out toe osteomyelitis, an MRI with contrast (gadolinium) is the preferred imaging study, as recommended by the most recent guidelines 1. This should include T1-weighted, T2-weighted, and STIR (Short Tau Inversion Recovery) sequences of the foot, with particular focus on the affected toe. The contrast enhancement helps distinguish between bone infection and other conditions like neuropathic changes or soft tissue inflammation. Some key points to consider when ordering an MRI for this purpose include:
- Informing the radiologist about any metal implants, pregnancy, kidney problems, or claustrophobia before the procedure 1
- No special preparation is typically needed, though removal of all metal objects is required
- The MRI's high soft tissue contrast and ability to detect bone marrow edema make it superior to other imaging modalities for diagnosing osteomyelitis, with sensitivity and specificity exceeding 90% 1 Early detection is crucial as untreated osteomyelitis can lead to bone destruction, deformity, and potentially amputation, especially in patients with diabetes or peripheral vascular disease. It's also important to note that while other imaging techniques like PET or leukocyte scintigraphy may be considered in certain cases, MRI remains the first-line choice for its balance of sensitivity, specificity, and availability 1.
From the Research
MRI Sequences for Diagnosing Toe Osteomyelitis
To rule out toe osteomyelitis, the following MRI sequences can be used:
- Fat-suppressed contrast-enhanced MR imaging, which has a high sensitivity and specificity for diagnosing osteomyelitis, especially in patients with complicating clinical factors 2
- Short-Tau Inversion-Recovery (STIR) sequences, which have a high sensitivity for osteomyelitis, but may require additional sequences such as T1-weighted spin echo sequences before and after contrast administration to increase specificity 3
- T1-weighted and T2-weighted MR imaging, which can help identify areas of bone necrosis and marrow abnormalities, but may not be as sensitive or specific as fat-suppressed contrast-enhanced MR imaging 4, 5
Key Findings
- Fat-suppressed contrast-enhanced MR imaging is more sensitive and specific than scintigraphy and nonenhanced MR imaging for diagnosing osteomyelitis, especially in patients with complicating clinical factors 2
- STIR sequences have a high sensitivity for osteomyelitis, but may require additional sequences to increase specificity 3
- Confluent low-signal intensity on T1-weighted images is not always present in osteomyelitis, but confluent high-signal intensity on T2-weighted images is often seen 5
- Central hypoenhancing regions of marrow without abscess formation, multiple foci of marrow replacement, and an irregular contour of marrow abnormality are common signs of osteomyelitis 5