Skin auto-fluorescence and impairment in thermal sensory testing in diabetes mellitus type 2

HbA1c and glucose control are only in part predicting diabetic polyneuropathy (DPN). In addition, the term „diabetic neuropathy” stands for very different disease entities, affecting the different types of nerve fibers, comprising the sensory-motor- or autonomic nervous system. Therefore we used skin auto-fluorescence, which partially reflects advanced glycation end products (AGE) accumulated in the skin, and quantitative sensory testing (QST), as well as heart rate variability as a surrogate parameter for autonomic neuropathy, to study whether all symptoms of DPN correlate in a similar manner with skin auto-fluorescence in 81 type 2 diabetic patients in a cross-sectional study. All statistical analyses were performed using non-parametric tests, correlations were calculated by Spearman and Kendall tau correlation coefficients.

As expected, diabetes duration correlated positively with skin auto-fluorescence, whereas no correlation between HbA1c and skin auto-fluorescence could be found. Concerning thermal sensory testing of the feet, there was a negative correlation between cold detection threshold (CDT) and skin auto-fluorescence, whereas the correlation with warm detection threshold was positive. Fittingly, thermal sensory limen (TSL) correlated positively with skin auto-fluorescence. In contrast, no correlations between mechanical sensory tests or heart rate variability and skin auto-fluorescence could be detected. Therefore, DPN comprises a variety of symptoms, which are not necessarily comparable. In addition, while symptoms are more prevalent in the lower extremities, comparable results concerning thermal sensory testing could be detected on the patients' hands, showing similar DPN affection of the upper extremities.