Prospective comparison of WBC SPECT/CT and conventional MRI for diagnosing osteomyelitis and monitoring treatment response in diabetic foot infections

Osteomyelitis is a common complication of diabetic foot ulcers and a leading cause of lower limb amputations globally. Accurate diagnosis of diabetic foot osteomyelitis (DFO) is essential for effective infection management and improving prognosis. This study aimed to compare the performance of white blood cell (WBC)-single photon emission computed tomography (SPECT)/computed tomography (CT) and conventional MRI in the initial diagnosis of DFO and in detecting residual infection during treatment monitoring, using bone biopsy as the reference standard.

In this prospective clinical study, 47 patients with foot wounds suspicious for DFO underwent 99mTc-WBC SPECT/CT and MRI, followed by bone biopsy. After receiving a standard course of antibiotics, 20 patients returned for post-treatment imaging and a repeat biopsy. All imaging studies and histopathology were blindly interpreted as positive or negative for DFO. Biopsies were considered positive if either bone cultures or histopathology indicated osteomyelitis. Imaging results were evaluated against biopsy to determine the diagnostic performance of each method before and after treatment.

For initial DFO diagnosis, WBC SPECT/CT demonstrated sensitivity, specificity, positive predictive value and negative predictive value of 85%, 79%, 90% and 69%, respectively, while MRI yielded corresponding values of 73%, 43%, 75% and 40%. Following antibiotic therapy, WBC SPECT/CT and MRI shared identical sensitivities, specificities, positive predictive values and negative predictive values of 75%, 75%, 43% and 92%.

WBC SPECT/CT exhibits greater sensitivity and specificity than MRI at initial diagnosis. However, after treatment, WBC SPECT/CT and MRI perform equivalently in determining therapeutic response. Our results indicate WBC SPECT/CT is a viable, if not superior, method for primary non-invasive assessment of suspected DFO. To our knowledge, this is the first study to use paired bone biopsy to validate imaging in diabetic foot infections both before and after antibiotic intervention.

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