External validation and optimisation of a model for predicting foot ulcers in patients with diabetes

Abstract

Aims/hypothesis In 2006 a risk stratification model was developed by Boyko et al. to predict foot ulceration in patients with diabetes, using seven commonly available clinical variables. We sought to validate and optimise this clinical prediction rule in a different setting. Methods A retrospective cohort study was conducted on all patients with diabetes attending the podiatry section of a diabetic foot clinic at a tertiary hospital in Portugal (n=360). Assessment at baseline included variables evaluated in the previous study and other relevant variables. Results Type 2 diabetes was present in 98% of patients, 45% were men and (at baseline) the median age was 65 years. Median follow-up was 25 months (range 3-86), during which 94 patients (26%) developed a foot ulcer. Boyko's model had an area under the receiver operating curve of 0.83 (95% CI 0.78-0.88). The corresponding value for the optimised model, which included the footwear risk variable, was 0.88 (95% CI 0.84-0.91). Both models had high classification accuracy for prediction of foot ulceration. However, the optimised model tended to produce higher specificity and positive likelihood ratio values at all levels. Conclusions/interpretation This study confirmed that Boyko's proposed model has a high capacity to predict foot ulceration in diabetes patients of both sexes. Our results suggest that the inclusion of a further footwear variable could improve the model. Nevertheless, prospective validation in a larger population is still necessary.

Risk stratification systems for diabetic foot ulcers: a systematic review

“…In univariate analysis, six of the seven variables included in the Boyko model were also significantly associated with foot ulcer development in the external validation study [25]. Tinea pedis, as in the Boyko et al study [24], showed a statistically significant association only in multivariate analysis [25].…”

“…It was only possible to analyse or calculate diagnostic accuracy measures (sensitivity, specificity, predictive values) in three studies [18,21,25] (Table 4). In the studies where diagnostic accuracy measures or crude data were not displayed, they were calculated by or requested from the authors [18,20,24], respectively.…”

“…The IWGDF system suffered modifications twice and its validation was performed accordingly [19,20]. The Boyko et al system was the only one externally validated [24,25]. Conversely, the IWGDF was the only group that applied worldwide dissemination techniques (manuals and CD distribution, website creation and others) for the system described in Apelqvist et al articles [9,14].…”

“…The Boyko et al stratification system, as originally proposed, was externally validated in a 2010 retrospective cohort study including 360 participants [25]. They were followed for 25 months (mean) and 26% developed an ulcer (using the same definition as in the study of Boyko et al [24]).…”

“…They were followed for 25 months (mean) and 26% developed an ulcer (using the same definition as in the study of Boyko et al [24]). Inability to feel the 10 g SWM at one or more of eight points (four in each foot) was considered to indicate diabetic neuropathy [25].…”