Better Islet Function and Cardiovascular Autonomic Function in Type 2 Diabetic Patients With Pure Small Fibre Neuropathy Than With Mixed Neuropathy

Abstract

BackgroundThe clinical characteristics and outcomes of small fibre neuropathy (SFN) in Chinese patients with type 2 diabetes have not been thoroughly described, and we investigated metabolic and neurological indexes and the prognosis of type 2 diabetic patients based on skin biopsy. MethodsThirty-four healthy Chinese volunteers were recruited for skin biopsy to establish the reference range of intraepidermal nerve fibre density (IENFD). Eighty-nine patients with type 2 diabetes from the Department of Endocrinology at Nanjing Drum Tower Hospital between December 2015 and April 2020 were included in the final study. Metabolic and neurological indexes were evaluated at baseline. Diabetic cardiovascular autonomic function was tested through cardiovascular autonomic reflex tests (CARTs). Seventeen pure SFN subjects and 9 mixed diabetic polyneuropathy (DPN) subjects were reassessed after the follow-up. ResultsLevels of HbA1c and postprandial blood glucose were lower (P=0.005 and P=0.041, respectively), while postprandial C-peptide and insulin were higher (P=0.001 and P=0.019, respectively) in the pure SFN group than in the mixed DPN group. Regarding the CARTs, the mixed DPN group obtained the highest score, indicating the worst cardiovascular autonomic neuropathy (CAN). Among the four CART items, postural BP change was lower while deep breathing max-min was higher in the pure SFN group than in the mixed DPN group (P=0.023 and P=0.040, respectively). A partial correlation showed that there was a negative correlation between IENFD of the distal leg and CART scores (r=-0.513, P=0.001) after adjusting for age and duration of diabetes. Only vitamin B12 (p=0.028) and motor nerve conduction velocity (MCV) of the common peroneal nerve (p=0.045) were increased in the 17 patients with pure SFN after the follow-up. However, MCVs of the common peroneal nerve (p=0.025) and tibial nerve (p=0.047) were decreased at the final visit in the mixed DPN group. ConclusionsBetter islet function and cardiovascular autonomic function were observed in patients with pure SFN compared with mixed DPN. CART scores were negatively correlated with IENFD in the distal leg even after adjusting for age and duration of diabetes. The metabolic and neurological indexes remained relatively stable in the follow-up of pure SFN subjects.