The early distinction between diabetic foot osteomyelitis and Charcot joint during initial phase leukocyte (WBC)/bone scan dual isotope SPECT/CT imaging

Objectives Dual isotope (DI) SPECT/CT WBC/bone scan (step1 DI) has been confirmed to be highly accurate for diabetic foot evaluation of osteomyelitis (OM)/soft tissue infection & exact localization of infection site. However, it may require a second day imaging with DI SPECT/CT WBC/bone marrow scan (step2 DI) following additional radiotracer injection when scan is positive in tarsal bones to differentiate true OM from bone marrow hyperplasia (BMH) WBC uptake, frequently noted in Charcot’s joint. This study evaluates other imaging parameters that can help distinguish between these two conditions prior to step2 DI imaging.

Methods 22 diabetic patients with suspected tarsal bone OM versus BMH by step1 DI were identified. Tc-99m sulfur colloid was injected & step2 DI were obtained the following day on all patients. Tarsal bone positive Lesions were classified as OM when bone marrow scan showed no corresponding uptake & BMH when bone marrow scan showed uptake similar to or greater than WBC uptake. Findings were correlated to presence of adjacent deep soft tissue infection (ADSTI), initial & delayed lesion WBC uptake ratios, & visual/quantitative rate of wash out of WBC (decreased delayed WBC ratio).

Results Out of 27 positive WBC tarsal bone lesions, 10 were consistent with OM, of which 9 showed ADSTI (p <0.005). WBC washout was seen in 15/17 BMH & in 0/10 OM lesions (p <0.001). WBC washout rates mean ± SE in OM & BMH were 0.99 ± 0.13 & 2.59 ± 0.47, respectively (p <0.005).

Conclusions Our preliminary data of step1 DI SPECT/CT imaging analyses of diabetic patients with suspected tarsal bones OM appear considerably useful in predicting true tarsal bone OM prior to proceeding with step2 DI. These early imaging findings may limit the need for subsequent delayed imaging in many patients. Moreover, additional administration of radiotracer for bone marrow scan could be mostly eliminated, which abide by FDA/SNMMI/RSNA initiative of reducing unnecessary radiation exposure.