The usefulness of quantitative 99mTc-HMPAO WBC SPECT/CT for predicting lower extremity amputation in diabetic foot infection

Abstract

We investigated the usefulness of quantitative ^99mTc-white blood cell (WBC) single photon emission computed tomography (SPECT)/computed tomography (CT) for predicting lower extremity amputation in diabetic foot infection (DFI). A total of 93 feet of 83 consecutive patients with DFI who underwent WBC SPECT/CT for treatment planning were retrospectively analysed. The clinical and SPECT/CT parameters were collected along with the measurements of the maximum standardized uptake value (SUVmax) at DFI. Statistical logistic regression analysis was performed to explore the predictors of LEA and receiver operating characteristic (ROC) curve was analysed to assess the predictive value of SPECT/CT. The independent predictors of amputation were previous amputation (OR 11.9), numbers of SPECT/CT lesions (OR 2.1), and SUVmax of DFI; either continuous SUVmax (1-increase) (OR 1.3) or categorical SUVmax > 1.1 (OR 21.6). However, the conventional SPECT/CT interpretation failed to predict amputation. In ROC analysis, the SUVmax yielded a fair predictor (area under the curve (AUC) 0.782) of amputation. The model developed from these independent predictors yielded an excellent performance for predicting amputation (AUC 0.873). Quantitative WBC SPECT/CT can provide new information useful for predicting the outcomes and guiding treatment for patients with DFI.

Figure 1

(a) Abnormal leukocyte accumulation was observed in the right 1st to 5th toes, with the radioactive lesions extending to the bone, indicating osteomyelitis (left panel, MIP image; right panel, axial SPECT/CT). Two spherical VOIs were drawn on DFIs and the highest SUVmax was 4.2 (higher than the cutoff of 1.1) Despite intensive treatment, the infection progressed, leading to the patient undergoing right below knee amputation 43 days after SPECT/CT. (b) Mild focal abnormal leukocyte accumulation was detected in the right 3rd and 4th toes. The lesions were in contact with the bone, which raised a suspicion of osteomyelitis (left panel, MIP image; right panel, axial SPECT/CT). A circular VOI was drawn on DFIs and the SUVmax was 1.0 (lower than the cutoff of 1.1). After 10 weeks of antibiotic treatment, the infection was successfully resolved, and the foot was preserved.

Figure 2

(a) The ROC curve illustrates the predictive performance of SUVmax for amputation in patients with DFI (AUC 0.782, 95% CI 0.684–0.861). The optimal SUVmax cutoff was identified as 1.1 (b) The ROC curves represent the predictive models derived from independent factors, including history of amputation, number of SPECT/CT lesions, and either continuous SUVmax (AUC 0.873, 95% CI 0.788–0.933) or SUVmax > 1.1 (AUC 0.865, 95% CI 0.778–0.927), or excluding SUVmax (AUC 0.790, 95% CI 0.693–0.868). Cont. indicates continuous, NS indicates not statistically significant; *, P < 0.05.