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

Abstract

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. Supplementary Information The online version contains supplementary material available at 10.1007/s13300-021-01111-0.

Small fiber neuropathy

“…5 SFN is frequently associated with large fiber neuropathy but occasionally damage of different fiber types is unequal and large fibers (vitamin B12 deficiency) or small fibers are predominantly or exclusively affected (Fabry disease). 6,7 Small fibers build up 80-90% of the peripheral nerves. 7 SFN can be the initial stage of a peripheral neuropathy with consecutive involvement of large fibers over time.…”

“…Aδ‐fibers conduct either sensory (somatic) or preganglionic autonomic (parasympathetic or sympathetic) and innervate sweat glands (sudomotor function), hair follicles (pilomotor function), or dermal vessels (vasomotor function) 5 . SFN is frequently associated with large fiber neuropathy but occasionally damage of different fiber types is unequal and large fibers (vitamin B12 deficiency) or small fibers are predominantly or exclusively affected (Fabry disease) 6,7 . Small fibers build up 80–90% of the peripheral nerves 7 .…”