Comparative Study Of Neuroelectrophysiological Methods On Evluating The Function Of Peripheral Nerves In Diabetic Patients

Objective:To investigate the the features of different nerve fiber dysfunction and the effects of the contact heat evoked potential(CHEP),nerve conduction study (NCS),F wave and skin sympathetic response(SSR) in evaluating the nerve fiber dysfunction of diabetic neuropathy.Methods:CHEP,F-wave of median nerve and NCS were performed in 50 diabetic patients and 50 normal control subjects.For CHEP,thermal stimuli were given at 52℃to 3 body sites:right forearm,right dorsum hand and right peroneal area.CHEP were recorded from Cz.The main components of CHEP were observed: N wave latency and N-P amplitude.Standard sensory and motor nerve conduction studies of median nerve,ulnar nerve,posterior tibial nerve and common peroneal nerve were performed in all diabetic patients and normal control subjects,respectively. SSR test was performed in all diabetic patients.Motor nerve conduction velocity (MCV),distal motor latency(DML) and amplitude of compound muscle action potential(CMAP),latency and amplitude of sensory nerve action potential(SNAP), sensory nerve conduction velocity(SCV) of all the nerves,amplitude and latency of SSR,latency of F-M wave and F wave were studied simultaneously.Results:1.There were no recordable CHEP on stimulation of the forearm,dorsum hand and the leg in some cases of diabetic patients.In contrast,CHEP were recordable in all control subjects.The diabetic group had reduced N-P amplitudes(P＜0.01) and prolonged N-wave latencies(P＜0.05)[patients vs controls,for the forearm:latencies: 400.72±29.93 vs 388.57±25.00,amplitudes(μV):28.2(18.9) vs 50.0(26.3);for the dorsum hand:latencies(ms):421.83±28.18 vs 407.79±28.95,amplitudes(μV): 23.3(15.6) vs 44.2(28.4);for the leg:latencies(ms):472.08±40.38 vs 449.64±30.35, amplitudes(μV):21.5(14.3) vs 38.2(29.9)].2.In patients with normal nerve conductions,amplitudes of CHEP were reduced and latencies of CHEP were prolonged[There were 27 patients with normal nerve conduction for upper limbs,their CHEP for the forearm:patients vs controls, amplitudes(μV):35.0(29.1) vs 50.0(26.3),P＜0.01.For the dorsum hand: latencies(ms):423.18±31.87 vs 407.79±28.95;amplitudes(μV):23.3(15.6) vs 44.2(28.4),P＜0.01.There were 19 patients with normal nerve conductions for lower limbs,their CHEP for the leg:patients vs controls,.latencies(ms):468.19±31.75 vs 449.64±30.35,P =0.044;amplitudes(μV):23.8(18.3) vs 38.2(29.9),P＜0.01].3.The mean visual analog scale(VRS) was significantly lower in diabetic patients than in control subjects(for control group:6.4±0.8,5.8±0.9,5.3±1.0;and for diabetic group:4.6±1.2,4.3±1.0,3.9±1.1,P＜0.05).4.There were a significant decrease in CHEP amplitude ratio of lower limb/upper limb in diabetic group than that in control group(P＜0.05).5.The diabetic group had prolonged DML,reduced amplitude of CMAP and MCV of median nerve,ulnar nerve,posterior tibial nerve and common peroneal nerve[eg,amplitudes of CMAP(mV):patients vs controls:8.99±2.41 vs 10.72±2.22, 8.51±2.02 vs 9.90±1.60,6.73±3.09 vs 8.81±3.40,4.23±1.85 vs 5.65±2.03,P＜0.01; MCV(m/s):53.39±4.44 vs 57.23±3.97,58.68±6.55 vs 64.91±5.71,45.75±5.01 vs 50.06±4.42,45.16±5.29 vs 49.71±5.84,P＜0.01],and also had reduced amplitude of SNAP,SCV of all the nerves[amplitudes of SNAP(μV):11.68±5.25 vs 19.47±6.94, 8.61±4.28 vs 11.89±4.63,1.29±0.51 vs 1.90±1.17,1.55±0.49 vs 2.02±0.79,P＜0.05; SCV(m/s):44.57±6.37 vs 50.53±5.15,52.26±5.98 vs 56.92±5.24,40.20±3.20 vs 42.67±4.09,51.89±7.61 vs 55.84±5.88,P＜0.05].The diabetic group also had prolonged DML of SNAP for median nerve and ulnar nerve(P＜0.05).6.More severe abnormal nerve conduction was found in lower limbs than in upper limbs.The abnormal degree was more severe in sensory nerve than in motor nerve and severity was more in amplitude than in conduction velocity(P＜0.05).7.In diabetic group,the F wave latencies[(ms):28.77±2.79 vs 26.67±1.87,P＜0.01],F-M latencies[(ms):25.50±2.87 vs 23.71±1.88,P＜0.01]were prolonged and conduction velocities of F wave were reduced[(m/s):61.64±5.24 vs 65.76±5.53,P＜0.01].8.In 29 patients with normal NCS of median nerve,no statistical difference was found in the F wave latencies,F-M latencies and conduction velocity compared with the control group.9.Abnormal SSR was detected in 15(55.6%) patients of the 27 diabetic patients with normal NCS of median nerve and ulnar nerve.There were 13(68.4%) patients had SSR abnormalities of lower limbs in the 19 diabetic patients with normal NCS of posterior tibial nerve and common peroneal nerve.More severe abnormal SSR was found in lower limbs than in upper limbs(P＜0.05).10.There was a severe abnormality of NCS than that of F wave in upper limbs(P＜0.05).The abnormal degree was more severe in sensory nerve than in motor nerve and F wave(P＜0.05).More severe abnormal was found in SSR than in NCS(P＜0.05).Conclusion:Peripheral nerve dysfunctions(motor,sensory,sympathetic and Aδsmall fiber) are detected in diabetic neuropathies.Both proximal and distal nerve segments could be affected by the diabetic neuropathy.Both axonal type injury and demyelinating injury could be found,but axonal type injury is more than demyelinating.Severity is more in sensory nerve than in motor nerve,and the small fiber is affected earlier than other nerve fibers in diabetic patients,both small and large fiber dysfunction are correlated with the length of nerves.More severity is found in lower limbs than in upper limbs.Electrophysiological tests are important in evaluating the early fiber dysfunction of diabetic neuropathy,and could be a sensitive means for the early diagnosis of diabetic neuropathy.