Predicting ulcer‐free survival using the discriminative value of screening test locations

Abstract

Background Current guidelines recommend screening the feet of diabetic subjects with a 10‐g monofilament or tuning fork. We investigated which tests and locations on the feet have the best predictive value regarding 1‐year ulcer‐free survival in diabetic subjects participating in the prospective Rotterdam Diabetic Foot Study. Methods Decision tree analysis was used to predict ulcer‐free survival based on responses from individual test locations (monofilaments on 10 sites, vibration sense was tested on both halluces and medial malleoli). Separate trees for patients with and without a history of diabetic foot ulcer (DFU) were developed. Results Four hundred sixteen subjects (mean [SD] age, 61.8 years [12.4]; range, 21.6‐90.2) were measured, of whom 24 developed new DFUs. Three tests exhibited discriminative and predictive properties: testing vibration sense on the medial malleolus and monofilament testing on heel and hallux. The decision tree to predict ulcer‐free survival in patients with a history of DFU yielded a sensitivity of 87.0%, which was 99.6% for the tree of patients without a history of DFU. Conclusion The findings of this study aids medical decision making by discriminating between high‐ and low‐risk patients of developing DFU using selective testing on sites with predictive properties.

Item reduction of the 39‐item Rotterdam Diabetic Foot Study Test Battery using decision tree modelling

“…Moreover, the multisensory modalities included in the RDF‐39 are reflected in the decision tree that was developed using modern statistical techniques. Decision tree analysis has been demonstrated useful in item reduction of questionnaires and test batteries and has been used in different fields of medicine . Several caveats relating to our study are important to highlight.…”

“…However, thresholds and cut‐off values on how many test sites to be used for predicting, for example, first‐onset DFU, are often conjectured . A recent study using prospective RDF study data showed that particular sites of monofilament and vibratory testing outperformed composite scores of tuning fork (up to four test sites) and 10‐g monofilaments (up to 10 test sites) in the prediction of ulcer‐free survival . It is the combination of sensory test and test site that allows for staging of sensory loss, according to recently developed grading scales, with both test and test site having predictive properties regarding the degree of sensory loss observed .…”

“…Within the consequent subgroups, CART will again identify the test item that provides an equal split, on the basis of the RDF‐39 sum score. The algorithm will stop when a maximum of three splits (ie, the maximal number of questions that is allowed, called “depth”) has been executed or when no more than 20 patients remain in a subgroup . Mean and standard deviations of RDF‐39 scores per subgroup are given.…”

Which diagnostic tests in everyday clinical practice are (not) useful in the management of diabetic foot disease?

“…Multiple clinical tests are available to detect signs of peripheral sensory neuropathy and include tests of loss of touch sensation (primarily 10 g monofilament). The use of tests of touch sensation has been shown to link to risk of the future development of new DFUs . Attention must be drawn, however, to there being no consistent guidance on which sites on the foot should be tested, how many should be tested and how many missing points of sensation constitutes abnormality.…”

“…The use of tests of touch sensation has been shown to link to risk of the future development of new DFUs. [4][5][6] Attention must be drawn, however, to there being no consistent guidance on which sites on the foot should be tested, how many should be tested and how many missing points of sensation constitutes abnormality. Resulting inconsistencies undermine the interpretation of such tests in everyday clinical practice.…”