Evaluation of Lower Extremity Calcium Score as a Measure of Peripheral Arterial Disease Burden and Amputation Risk.

BACKGROUND: The ankle-brachial pressure index (ABI) and toe-brachial pressure index (TBI) are commonly used diagnostic tools for peripheral artery disease (PAD) that are unreliable in the presence of calcified vessels.In this study, we aimed to demonstrate the utility of lower extremity calcium score (LECS) in addition to ABI and TBI in measuring disease burden and predicting the risk of amputation in patients with PAD.

METHODS/RESULTS: Patients who were evaluated in the vascular surgery clinic at Emory University for PAD and who underwent non-contrast CT of the aorta and lower extremities were included in the study. Aorto-iliac, femoral-popliteal, and tibial calcium scores were measured using the Agatston method. ABI and TBI that were obtained within 6 months of the CT scan were noted and divided into categories of PAD severity. Associations between ABI, TBI, and LECS of each anatomic segment were evaluated. Univariate and multivariate ordinal regression analysis were performed to predict the outcome of amputation. ROC analysis was performed to compare LECS with other variables in its ability to predict amputation.

RESULTS: 50 patients included in the study cohort were divided into LECS quartiles, with 12-13 patients in each quartile. The highest quartile tended to be older (p=0.016), had higher percentage of diabetics (p=0.034), and higher frequency of major amputation (p=0.004) compared to the other quartiles. Patients in the highest quartile of tibial calcium score were more likely to have stage 3 CKD or greater (p=0.011) and also had a higher frequency of amputation (p<0.005) and mortality (p=0.041). We found no significant association between each anatomic LECS and ABI/TBI categories. On univariate analysis, CKD (OR 12.92 [95% CI 2.01-82.83], p=0.007), DM (OR 5.47 [95% CI 1.27-23.64], p=0.023), tibial calcium score (OR 6.62 [95% CI 1.79-24.54], p=0.005) and total bilateral calcium score (OR 6.32 [95% CI 1.18-33.78], p=0.031) were associated with increased risk of amputation. On multivariate stepwise ordinal regression, TBI and tibial calcium score were identified as important predictors of amputation with HLD and CKD increasing the overall prediction of the model. On ROC analysis, the addition of tibial calcium score (AUC 0.94, SE 0.048). significantly improved the prediction of amputation compared to HLD, CKD and TBI alone (AUC 0.82, SE0.071, p=0.022).

CONCLUSIONS: The addition of tibial calcium score to other known PAD risk factors may improve the prediction of amputation in patients with PAD.