Nerve Excitability Study In Early Diabetic Peripheral Neuropathy

[Objective]:The experiment aimed at exploring the significance of nerve threshold in diagnosing diabetic peripheral neuropathy, especially subclinial diabetic peripheral neuropathy (DPN); exploring the significance of nerve action potential amplitude in diagnosising DPN; exploring to analysis the correlation among the disease duration, the level of serum glucose, nerve threshold, and nerve action potential amplitude in patients who had disturbance of carbohydrate metabolism. We intented to find a new electrophysiologic examination method, which can be used to diagnose DPN, and can provide a help to observe the extent and therapeutic effect of DPN, add new electrophysiological indexs into researching DPN, thereby improving the diagnosis rate of DPN.[Method]:A total of 80 subjects were recruited, including 20 patients with impaired glucose tolerance(IGT),20 patients with type 2 diabetes with a disease duration of less than two years,20 patients with type 2 diabetes with a disease duration of 5-10 years and 20 age-matched healthy subjects, respectively. All subjects received a detailed physical examination performed by neuropathist, The neural symptoms of all patients were evaluated using the Neuropathy Symtom Score (NSS),the Neuropathy Disability Score (NDS) and the Michigan Neuropathy Screening Instrument (MNSI) before Electroneurophysiology examination. Patients who met recruiting criterion were arranged in a quite, shielding electrophysiologic examination room. The neural threshold of bilateral median nerve, ulnar nerve peroneal nerve and sural nerve in every subjects were measured using Medelec Synergy produced by Oxford instruments Medical Limited. The initial negative phase amplitudes of neural distal CMAP, latency, conduction velocity were recorded from bilateral median nerve, ulnar nerve peroneal nerve. The SNAP peak-peak amplitudes,latency,conduction velocity of bilateral sural nerve were recored. Moreover, the serum level of hemoglobin A1C (HbA1C) in all patients were recored. Then after, all datas were analyzed using the softwave SPSS.[Results]:1. Age and gender:there were no significant difference in age and gender among the IGT group, the short disease duration group,the long disease duration group and age-matched healthy subjects.2. The characteristic of neural threshold in healthy subjects:the distal neural threshold of bilateral median nerve, ulnar nerve in upper limb were higher than bilateral peroneal nerve of lower limb(P>0.05); Paired samplesT test showed there was no significant difference between the right limb and the left limb for bilateral median nerve, ulnar nerve, peroneal nerve and sural nerve(P> 0.05). Height was not a significant factor influencing neural threshold in all measured nerves(P> 0.05); Gender was also not a significant factor influencing neural threshold in all measured nerves (P>0.05).3. The characteristic of nerve action potential amplitude in healthy subjects:There was no significant difference between the right limb and the left limb for the negative phase amplitudes of distal CMAP in median nerve, ulnar nerve, peroneal nerve, and for SNAP peak-peak amplitudes in sural nerve, There was also no statistical difference between genders for the negative phase amplitudes of distal CMAP in median nerve, ulnar nerve, peroneal nerve, and for SNAP peak-peak amplitudes in sural nerve. Statistical analysis showed that there was no significant difference among different ages for the negative phase amplitudes of distal CMAP in median nerve, ulnar nerve, peroneal nerve, and for SNAP peak-peak amplitudes in sural nerve among 20-40 years old.4. The correlation between neural threshold and neural action potential amplitude: there was a reverse linear correlation between diatal neural threshold of motor never and distal CMAP negative amplitudes of motor nerve in healthy subjects, the value of r was-0.46 (P<0.0001). There also was a reverse linear correlation between sensory neural thershold of sural nerve and SNAP peak-peak amplitudes of sural nerve in healthy subjects, the value of r was-0.38(P<0.05); In the IGT group, there was a reverse linear correlation betwee diatal neural threshold of motor never and distal CMAP negative amplitudes of motor nerve, the value of r was-0.26 (P<0.01), whereas, the sural sensory neural threshold was not correlated to the sural SNAP peak-peak amplitudes(P>0.05); In the short disease duration DM group, there was a reverse linear correlation between diatal neural threshold of motor never and distal CMAP negative amplitudes, r was-o.39 (p<0.0001), the sural sensory neural threshold was not correlated to the sural peak-peak SNAP amplitudes (P>0.05); There was a reverse linear correlation between diatal neural threshold of motor never and distal CMAP negative amplitude of motor nerve in the long disease duration DM group, r was-o.49 (P<0.0001), the sural sensory neural threshold with a advese linear correlation to the sural peak-peak SNAP amplitudes, r was-0.35 (P<0.05).5. The correlation between neural threshold and disease duration, serum level of hemoglobin A1C:the distal motor neural threshold of bilateral median nerve, right peroneal nerve and the sesory neural threshold of bilateral sural nerve gradually increase wiht the disease duration of carbohydrate metabolic disorder extends (P<0.05). The distal motor neural thresholds of right median nerve, right peronea nerve and the sensory neural threshod of bilateral sural nerve in the IGT group were higher than that of the healthy groups, however, there was no statistical difference in the distal motor neural threshold of left median nerve, bilateral unlar nerves, left peroneal nerve and the sesory neural threshold of left sural nerve in between the IGT group and the healthy group. The data showed that the distal motor neural threshold of bilateral median nerve, left peroneal nerve and the sesory neural of bilateral sural nerves in the short disease duration DM group were higher than that of the healthy group, but there was no statistical difference in the distal neual threshold of bilateral ulnar nerve, left peroneal nerve between the short disease duration DM group and the heathy group; The distal neural threshold of bilateral median nerves, right ulnar nerve, bilateral peroneal nerves and the sensory neural threshold of bilateral sural nerves in the long disease duration DM group were higher than the healthy contol group, there was no diffence in the distal neural threshold of left ulnar nerve between the long disease duration DM group and the healthy control group. Between the IGT group and the short disease duration DM group, the mean of the distal neural threshold of right median nerve in the short disease duration was lower than that of the IGT group, but the statistics displayed there was no diffence (P>0.05). Howerve, the statistics showed the distal motor neural threshold of bilateral peroneal nerves and the sensory neural threshold of right sural nerve in the long disease duration DM group were lower than that of the short disease duration DM group(P<0.05). There was a positive linear correlation between the the distal neural threshold of left median nerve, right ulnar nerve, bilateral peroneal nerves and the sensory neural threshold of bilateral surai nerves in all patients and the serum level of hemoglobin A1C, the vaule of r were 0.33,0.34,0.30,0.27, 0.27,0.32, respectively (P<0.05), whereas, there were no correlation between the distal motor neural threshold of right median nerve, left ulnar nerver and the serum level of hemoglobin A1C (P>0.05).6. The corelation between neural action potential amplitude and the disease duration, the serum level of hemoglobin A1C:the distal CMAP negative amplitudes of bilateral median nerve, bilateral peroneal nerve and the SNAP peak-peak amplitudes of bilateral sural nerve gradually decreased with the disease duration of carbohydrate metabolic disorder extends (P<0.05). There was no significant difference in the distal CMAP negative amplitudes of bilateral media nerve, bilateral ulnar nerve, bilateral peroneal nerves and the SNAP peak-peak amplitudes of bilateral sural nerve between the IGT group and the healthy control group (P>0.05); The distal CMAP negative amplitudes of bilateral median nerves, left ulnar nerve and the SNAP peak-peak amplitudes of bilateral sural nerves in short disease duration DM group were lower than that of the healthy control group(P<0.05), but there were no statistical difference in the distal CMAP negative amplitudes of right ulnar nerve, bilateral peroneal nerves and the SNAP peak-peak amplitudes of right sural nerve between the short disease duration DM group and the healthy control group(P>0.05). The distal CMAP negative amplitudes of bilateral median nerves, right ulnar nerve, bilateral peroneal nerves and the SNAP peak-peak amplitudes of bilateral sural nerves in the long disease duration DM group were lower than that of the healthy group(P<0.05), there was no difference in the distal CMAP negative amplitudes of left ulnar nerve between the short disease duration DM group and the healthy control group(P>0.05); The distal CMAP negatives amplitude of bilateral median nerves, left ulnar nerve, left peroneal nerve in the short disease duration DM group were lower than that of the IGT group(P<0.05), there were no significant difference in the distal CMAP negative amplitudes of right ulnar nerve, right peroneal nerve and the the SNAP peak-peak amplitudes of bilateral sural nerves between the IGT group and the short disease duration DM group(P>0.05); Datas displayed that the distal CMAP negative amplitudes of left median nerve, left ulnar nerve in the long disease duration DM group were higher than that of the short disease duration DM group, but the statistics showed there was significant difference only in the distal CMAP negative amplitudes of left median nerve between the short disease duration DM group and the long disease duration DM group(P<0.05).[Conclusion]:1,The distal neural threshold and CMAP negative amplitudes of motor never in bilateral media nerves, bilateral ulnar nerves, bilateral peroneal nerves and the sensory neural threshold and SNAP peak-peak amplitudes in bilateral sural nerves in healthy subjects were reliable and reproducible, they may be used to evaluate the functional status of peripheral nerve and the degree of nerve damaged.2,Neural excitability threshold measurements may detecte the changes of peripheral nerve excitability earlier,and provide help for the diagnosis of subclinic DPN.3,In the different stage of carbohydrate metabolic disorder, the degee of nerve damaged was not identical, there was a positive linear correlation between most of neural thresholds and the disease duration, there was a reverse linear correlation between most of neural thresholds and the disease duration and the level of serum glucose, there was a reverse linear correlation between most of neural amplitudes and the disease duration, there was no significant difference between most of neural amplitudes and the level of serum glucose.4,Combined application neural excitability threshold measurements with neural action potential amplitude measurements not only facilitate the detection of subclinical DPN, improving the diagnosing rate of subclinical DPN, but also increase the reliability of assessment about the degree of peripheral nerve fibers damaged in patients, assessing clinical efficacy, directing clinical treatment.