Background and aims: Intraepidermal nerve fibre density (IENFD) quantification is regarded to be a sensitive and specific measure of small nerve fibre dysfunction and IENFD loss is an early feature in glucose dysregulation. Our aims were to study IENFD in individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and type 2 diabetes (T2D) and to study if IENFD was associated to metabolic traits, e.g. obesity and dyslipidemia, and to neurophysiologic assessments of nerve function.
Materials and methods: Participants were consecutively recruited from the population-based Västerbotten Intervention Program; NGT (n=22), IGT (n=14), T2D (n=24), at the age of 60±1 years. The individuals’ height and weight were measured. Blood glucose and lipids were measured. Nerve conduction studies (NCS) were performed (sural and peroneal nerves) and the results were standardized to z-scores and compiled into a composite Z-score representing the nerve function in the leg. Neuropathy disability score (NDS) was used to evaluate neuropathic signs. In addition, thermal threshold tests (TTT) were performed to assess small nerve fibre function. Skin biopsies were performed using a 3-mm punch taken 10 cm proximal to the lateral malleolus. The intraepidermal nerve fibres were evaluated by routine immunohistochemistry and stained with anti-PGP9.5 (ubiquitin carboxyl-terminal hydrolase) antibodies. Light microscopy was used to identify nerve fibres in thin sections (5 µm) according to a standardized protocol. The IENFD was given as the mean of counts in 3 sections per millimeter of epidermal length. The assessors were blinded to the identity of the samples.
Results: Patients with diabetes had lower IENFD (median 2.9 nerves mm-1, IQR 1.2-4.8) than controls (median 4.4 nerves mm-1, IQR 3.5-6.3; Mann-Whitney U test p=0.007). IGT individuals did not differ in IENFD (median 3.2 nerves mm-1, IQR 1.4-5.5) compared to controls (p=0.12) or diabetic patients (p=0.53). IENFD was positively correlated to NCS (r=0.39, p=0.002), but not to TTT and NDS. Individuals in the 3rd tertile of composite Z-score (i.e. better nerve conduction) had higher IENFD (median 4.1 nerves mm-1, IQR 2.7-5.8) than individuals in the 1st tertile (median 2.4 nerves mm-1, IQR 0.7-3.9; p=0.009). Triglycerides and cholesterols were not associated with IENFD. However, a stepwise multiple linear regression analysis revealed that weight was independently associated to IENFD, after adjustment for age, sex, height, and diabetic status (β=-0.419, p<0.001).
Conclusion: We conclude that skin biopsies for IENFD quantification in thin sections is a simple useful method for assessing small nerve fibre neuropathy in individuals with diabetes. The association between weight and IENFD indicates that metabolic traits other than glucose dysmetabolism might play a role in the development small nerve fibre neuropathy.
47th Annual Meeting of the European Association for the Study of Diabetes (EASD), Lisabon, Portugal 12-16 September 2011