Is Toe Brachial Index a Better Tool than Ankle Brachial Index for Predicting Outcomes in Diabetic Foot Patients?

Abstract

Introduction: Diabetes accounts for more than 50% of lower extremity amputation, of which 85% of lower limb amputation in diabetic patients are preceded by foot ulcers. The increasing prevalence of ischaemic ulcers has made ischaemia probably the most important cause of Diabetic Foot Ulcers (DFUs) today. Modalities for assessment of vasculopathy include clinical examination of pulses, Ankle Brachial Pressure Index (ABI), Toe Brachial Pressure Index (TBI), Transcutaneous partial pressure of Oxygen (TCpO2), Duplex imaging, Magnetic Resonance (MR) and Computed Tomography Angiography (CTA). Aim: This study was aimed at evaluation of ABI and TBI in assessment of vasculopathy in DFUs and their association with the various surgical outcomes. Materials and Methods: This study was done as a cross-sectional study on 100 patients with diabetic foot, from December 2016 to April 2018, with prospective follow-up till the outcome of “ulcer healed”, “minor/major amputation” with healing of the amputation stump, was achieved. The multimodality approach for treatment of DFU was taken. Variables like age, gender, duration of present ulcer, previous history of ulcers and interventions, comorbidities, history of smoking and duration of diabetes were recorded and assessed. The examination included examination of peripheral pulses, presence of neuropathy, measurement of ABI and TBI. Investigations included HbA1c levels, swab or pus cultures from the ulcers, objective evaluation of Peripheral Arterial Disease (PAD) by Duplex Ultrasonography and CT Angiography where an intervention was contemplated. The data was entered in MS Excel spreadsheet and analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0. Results: The mean age was 62.55±9.21 years, with maximum patients belonging to the age group 61-70 years (38%) followed by 51-60 years age group (33%). Smoking as a risk factor was present in 59% of all the patients. A total of 53 patients underwent amputation among which 28 were smokers (52.8%). Neuropathy was present in 47.22% (n=51), with 60.87% of all patients with neuropathy undergoing amputation which was significant (p-value=0.005). When defined by ABI alone (ABI <0.9), 46.3% patients had PAD, however, using TBI <0.7 for defining PAD, incidence of PAD increased to 68.31% patients. Thus identifying 21 more patients with PAD as compared to ABI. Poor glycaemic control was significantly associated with poor outcome in the form of amputation (p<0.001). Patients who underwent major amputation had a mean ABI of 0.54±0.22, for minor amputation the mean ABI was 0.85±0.19 and for those who had healed ulcers, had a mean ABI of 0.61±0.27. The cut-off value for ABI to predict amputation was >0.51 with a sensitivity of 77.14 and a specificity of 56.1, which was not found to be significant (p-value=0.0796). The mean TBI for the diabetic feet was 0.25±0.12 for major amputation, 0.42±0.26 for minor amputation and 0.61±0.19 for ulcer healed. With a cut-off value of ≤0.3, the sensitivity and specificity for predicting amputation were 68.75 and 88.68 respectively which was found to be significant (p<0.001). Conclusion: The ABI has been found to under-report ischemia as compared to TBI in diabetic patients. TBI also correlates better with the outcome of a DFU. Thus, making TBI a part of assessment of vasculopathy in DFU patients who have not undergone toe amputations, would help in correctly identifying ischemia and early institution of possible intervention in such patients.