Association of Small Fiber Function with Microvascular Perfusion of Peripheral Nerves in Patients with Type 2 Diabetes : Study using Quantitative Sensory Testing and Magnetic Resonance Neurography.

Introduction/aims: Diabetic small fiber neuropathy (SFN) is caused by damage to thinly myelinated A‑fibers (δ) and unmyelinated C‑fibers. This study aimed to assess associations between quantitative sensory testing (QST) and parameters of peripheral nerve perfusion obtained from dynamic contrast enhanced (DCE) magnetic resonance neurography (MRN) in type 2 diabetes patients with and without SFN.

Methods: A total of 18 patients with type 2 diabetes (T2D, 8 with SFN, 10 without SFN) and 10 healthy controls (HC) took part in this cross-sectional single-center study and underwent QST of the right leg and DCE-MRN of the right thigh with subsequent calculation of the sciatic nerve constant of capillary permeability (K^trans), extravascular extracellular volume fraction (V_e), and plasma volume fraction (V_p).

Results: The K^trans (HC 0.031 min^-1 ± 0.009, T2D 0.043 min^-1 ± 0.015; p = 0.033) and V_e (HC 1.2% ± 1.5, T2D: 4.1% ± 5.1; p = 0.027) were lower in T2D patients compared to controls. In T2D patients, compound z‑scores of thermal and mechanical detection correlated with K^trans (r = 0.73; p = 0.001, and r = 0.57; p = 0.018, respectively) and V_e (r = 0.67; p = 0.002, and r = 0.69; p = 0.003, respectively). Compound z‑scores of thermal pain and V_p (r = -0.57; p = 0.015) correlated negatively.

Discussion: The findings suggest that parameters of peripheral nerve microcirculation are related to different symptoms in SFN: A reduced capillary permeability may result in a loss of function related to insufficient nutritional supply, whereas increased capillary permeability may be accompanied by painful symptoms related to a gain of function.