Better Islet Function and Cardiovascular Autonomic Function in Chinese Type 2 Diabetic Patients with Pure Small Fiber Neuropathy than with Mixed Neuropathy

Introduction The clinical characteristics and outcomes of small fiber neuropathy (SFN) in Chinese patients with type 2 diabetes mellitus (T2DM) have not been thoroughly described. In this study, we investigated the metabolic and neurological indexes and the prognosis of patients with T2DM based on skin biopsy. Methods A total of 34 healthy Chinese volunteers were recruited for skin biopsy to establish the reference range of intra-epidermal nerve fiber density (IENFD), and 89 patients with T2DM attending the Nanjing Drum Tower Hospital were evaluated at baseline. Of these 89 patients, 17 with pure SFN and nine with mixed diabetic polyneuropathy (DPN) were reassessed at the end of the follow-up. Results Glycated hemoglobin and postprandial blood glucose levels were lower ( P = 0.005 and P = 0.041, respectively) and postprandial C-peptide and insulin levels were higher ( P = 0.001 and P = 0.019, respectively) in the pure SFN group than in the mixed DPN group. A partial correlation study showed that there was a negative correlation between IENFD of the distal leg and cardiovascular autonomic reflex test (CART) scores ( r = − 0.513, P = 0.001) after adjusting for age and duration of diabetes. Only vitamin B12 level ( P = 0.028) and motor nerve conduction velocity (MCV) of the common peroneal nerve ( P = 0.045) were increased in the patients with pure SFN at the final visit while MCVs of the common peroneal nerve ( P = 0.025) and tibial nerve ( P = 0.047) were decreased in the mixed DPN group at the final visit. Conclusion Better islet function and cardiovascular autonomic function were observed in patients with pure SFN compared with mixed DPN. The metabolic and neurological indexes remained relatively stable in the patients with pure SFN during the follow-up.