Effects of impaired glucose regulation on large and small fibers in peripheral nerve

Abstract

Objective To use nerve conduction study (NCS) to evaluate the function of large fibers, skin sympathetic response (SSR) and contact heat evoked potential (CHEP) to evaluate the function of small fibers in patients with impaired glucose regulation (IGR), and to analyze the occurrence of peripheral neuropathy and damage characteristics. Methods According to the classification criteria of glucose metabolism proposed by WHO in 2006, we selected 120 patients with IGR from January 2015 to December 2016 in our hospital, including 37 impaired fasting glucose (IFG) patients, 83 impaired glucose tolerance (IGT) patients, and 60 normal subjects served as control group. All subjects received median, ulnar, tibial, peroneal, sural NCS, SSR and CHEP using the Keypoint.net (Medoc Ltd) electromyogram device. IGR patients were evaluated using the Michigan Neuropathy Screening Instrument (MNSI). Results The abnormal rate of MNSI score in IGR patients was 18.3% (22/120); the abnormal rate of NCS was 22.5% (27/120), and the abnormal rate of SSR was 39.2% (47/120). In IFG group, the above-mentioned abnormal rates were 8.1% (3/37), 13.5% (5/37), 29.7% (11/37) respectively, and 22.9% (19/83), 26.5% (22/83), 43.4% (36/83) in IGT group. Compared with control group, the tibial, sural nerve sensory nerve action potential amplitude decreased in IGT group (1.3(0.1, 1.9)μV vs 1.4(1.1, 3.2) μV, Z=-3.05, P=0.002; (10.5±2.0)μV vs (7.6±1.9)μV, t=0.60, P=0.001); and there was no significant difference between IFG patients and control group. Compared with control group, IFG patients′ SSR amplitude reduced in lower limbs (0.7(0.4, 0.8)mV vs 0.8(0.6, 1.0)mV, Z=-2.95, P=0.003), CHEP amplitude decreased in dorsum hand and peroneal area stimuli ((63.0±10.0)μV vs(52.4±15.3)μV, t=0.61, P=0.003; (44.7±12.5)μV vs (28.2±10.6)μV, t=0.31, P=0.000); and in IGR group, SSR amplitude reduced in upper and lower limbs (1.1(0.5, 2.2)mV vs 1.3(0.7, 2.6)mV, Z=-2.12, P=0.030; 0.4(0.2, 0.8)mV vs 0.8(0.6, 1.0) mV, Z=-5.96, P=0.000), CHEP amplitude decreased in dorsum hand and peroneal area stimuli ((63.0±10.0)μV vs (38.7±13.5)μV, t=0.37, P=0.000; (44.7±12.5)μV vs(21.9±13.6)μV, t=0.35, P=0.000). Conclusions There is peripheral neuropathy in IGR patients, and the incidence of neuropathy in patients with IGT is higher than those with IFG. Neurophysiological methods are earlier than clinical scores to detect neuropathy. There are only small fiber damages in IFG patients, and IGT patients present by large and small fibrous lesions, mainly in small fibers and lower sensory nerve fibers, characterized by axonal damage and length dependence. Key words: Glucose metabolism disorders; Peripheral nerves; Neural conduction; Evoked potentials; Evaluation studies