IDF21-0223 Diabetic foot ulcers’ impact on survival: an association study using the conditional inference tree approach

Abstract

Background: Up to a third of people with diabetes worldwide will develop a diabetic foot ulcer (DFU) during their lifetime. DFUs precede 80% of limb amputations (LEA). At five years, mortality after diabetes-related LEA exceeds 70%, and the risk of death for people living with DFU is 2.5 times the risk for those without one. However, risk factors are still not fully understood. Aim: To study the association between DFU and mortality in adults with diabetes adjusted for modifiable and non-modifiable risk factors. Method: Cohort with 595 adults with diabetes who attended a Podiatry appointment at a Portuguese Diabetic Foot Outpatient Clinic, from January 2010 to March 2013, and followed up to 31 December 2020, or death. The conditional inference tree (CIT) was used to identify predictors of mortality. CIT is a nonparametric statistical model used for making classifications or predictions based on tree-structure recursive partitioning. The variables considered were: age, gender, diabetes duration, insulin therapy, glycemic control, living alone, retinopathy, physical impairment, visual impairment, nephropathy, lower limb revascularization, diabetic peripheral neuropathy (DPN), cardiovascular disease, previous DFU, previous LEA, hypolipidemic and anticoagulant agents. All the statistical analyses were carried out using the package partykit, in R software. Results: At baseline, diabetes median duration was 15 (IQ [inter-quartile] range 10-23) years, with the participants' median age of 67.3 (59.2-75.4) years. Participants were mostly male (57.1), with previous DFU (54.4%), with DPN (56.5%) and cardiovascular disease (83.4%); 10.7% had previous LEA, 46.4% had retinopathy, 19.3% nephropathy. During a median follow-up of 8.1 (IQ range 3.9-9.3) years, there were 318 (53.4%) deaths. The predictors of all-cause mortality identified by the CTI were previous DFU, age, and retinopathy. At the end of eight years of follow-up, the estimated survival probability (95% CI [confidence interval]) was 47.5 (35.6-63.4) % for people without a previous DFU, aged older than 65 years, and with retinopathy. For those without retinopathy, it was 73.7 (64.6-84.0) %. For people with a previous DFU and older than 65, the eight-year estimated survival probability was 25.0 (19.6-31.9) %, while for the younger ones, it was 56.9 (48.5-66.6) %. Retinopathy did not impact the survival probability for people with previous DFU. Discussion: In this cohort of adults with diabetes, age, previous DFU, and retinopathy were the risk factors with a significant association with mortality. For participants with previous DFU, the highest mortality was observed for those aged older than 65. However, for adults with no previous DFU, mortality was associated not only with being older than 65 years but also with retinopathy. Retinopathy and DFU, both frequent, preventable and markers of diabetes control, significantly affected survival after adjustment for age.