Predicting response to therapy of diabetic foot infection utilizing high resolution 99mTc-WBC SPECT-CT fusion imaging

Objectives Determine if a staging system based on WBC SPECT-CT findings can predict response to antimicrobial therapy(abx tx) and clinical outcome of patients(pts) with diabetic feet infections.

Methods Retrospective blinded evaluation of WBC SPECT- CT of 100 clinically infected feet using a staging system based on CT evidence of cortical involvement as well as WBC SPECT intensity, extent, and proximity to bone cortex. The resultant Composite Severity Index (CSI), which ranged from 0(negative) to 13(severe osteomyelitis), was developed from those imaging features. Clinical outcome was determined by response to abx tx. The outcome could be either tx success or failure, whereas tx failure is defined by persistent signs of infection (intermediate outcome), readmission and/or amputation (worst outcome) during a 12 week post abx tx follow up. CSI was tabulated against probability(P) of therapy success and the worst outcome.

Results 42/100 (42%) of infected feet were treated successfully, 14/100 (14%) had intermediate outcome, and 44/100 (44%) had the worst outcome. Pts with the lowest CSI had 92 % P of tx success and 8% P of the worst outcome. Those with the highest CSI had 25% P of tx success and a 75% P of the worst outcome (see table).

Conclusions Based on feature extraction from SPECT-CT WBC imaging of diabetic foot infection, we have developed CSI, which is predictive of clinical outcome after abx tx. The chance of tx success decreased with increasing CSI. Conversely, as CSI increased, the chance of worst outcome increased incrementally

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Clinical Outcomes