Nerve Conduction Studies In Amyotrophic Lateral Sclerosis And Cervical Spondylotic Myelopathy

Background:Amyotrophic lateral sclerosis(ALS) is a neurodegenerative disease that result in progressive loss of bulbar and limb function. The pathogenesis of ALS remains unclear and there is no effective treatment. It may not draw your attention at the beginning of the disease, so many patients are misdiagnosed or never diagnosed. As the disease progresses, muscles of throat, limbs and thorax will become weaker and weaker until respiratory failure. So it is significance to make a definite diagnose early. The diagnosis of ALS depends on the clinical feature and electrophysiology, especially electromyography. Motor conduction studies are essential in the diagnosis of ALS. We research the feature of F-wave and moter conduction in patients of ALS and CSM/LSM, in order to make a clear diagnosis and differential diagnosis.Objective:To evaluate the relationship between the disease duration, muscle strength and the symptom of lower motor neuron, we retrospectively study the clinical and electrophysiological features in the patients that have been diagnosed ALS. We also compared the electrophysiological features between ALS and cervical spondylotic myelopathy (CSM)/lumbar spondylotic myelopathy (LSM) to make a clear differential diagnosis.Methods:We collected patients of confirmed ALS, CSM and LSM in Peking Union Medical College Hospital between June2012and April2013. Their clinical electrophysiological features including name, gender, age, disease duration, onset site, status of consent, pyramidal sign, myodynamia and result of nerve conduction and EMG were recorded and analyzed using statistical methods.Result:A total of137patients of ALS were recruited in our study including23definite ALS,70probable ALS and44possibleALS. The ratio of male:female in patients was1.91:1. The mean age of onset was51.19±10.57years. The onset site of disease were cervical myotomes (56.2%), lumbosacral myotomes (26.3%) and bulbar (17.5%).In the F-wave study among ALS patients in median nerve and posterior tibial nerve,87(71.9%) and8 (33.3%) had a low F-wave frequency,46(38%) and3(12.5%) had no F-wave,15(12.4%) and11(45.83%) had a prolonged F-wave mean latency. The patients who had a poor muscle strength had a lower F-wave frequency, higher ratio of no F-wave, prolonged F-wave mean latency, and increased F-wave dispersion than that have a better muscle strength. The reduction of F-wave frequency had a significant relationship with the UK Medical Research Council (MRC) scale (P<0.001) and atrophy of muscle (P <0.001).134median nerves,124ulnar nerves,47posterior tibial nerves and40common peroneal nerves were tested in the study of motor nerve conduction.3(3.23%) median nerves,1(0.81%) ulnar nerves,0(0%) posterior tibial nerves and4(10.00%) common peroneal nerves did not have a definite wave of motor conduction. In the motor conduction of median nerve,31(23.13%) had a prolongation of distal motor latency (DML), and92(68.66%) had a reduction of compound muscle action potential (CMAP) amplitude. In the motor conduction of ulnar nerve,19(15.32%) had a prolongation of DML, and73(58.87%) had a reduction of CMAP amplitude. In the motor conduction of posterior tibial nerve,3(6.38%) had a prolongation of DML, and19(40.43%) had a reduction of CMAP amplitude. In the motor conduction of common peroneal nerve,6(15.00%) had a prolongation of DML, and18(45.00%) had a reduction of CMAP amplitude. The reduction of CMAP amplitude had a significant relationship with onset site(P<0.001), the MRC scale(P<0.001)and atrophy of muscle(P<0.001). Only3patients had a abnormal sensory conduction.A total of27patients of CSM were recruited in our study. The mean age of onset was53.67±12.78years. A total of32patients of LSM were recruited in our study. The mean age of onset was55.69±19.25years. Compared with these patients, patients of ALS had a obviously prolonged DML (P<0.001), lower CMAP amplitude (P<0.001), lower F-wave frequency (P<0.001), slow F-wave velocity (P<0.001) and prolonged F-wave mean latency (P<0.05). Patients of ALS have a significantly prolonged DML, significantly lower CMAP amplitude, significantly lower F-wave frequency and prolonged F-wave latency than patients of CSM with the same MRC scale. Also, patients of ALS have a prolonged DML, lower CMAP amplitude, lower F-wave frequency and prolonged F-wave latency than patients of LSM with the same MRC scale. The mean disease duration of low F-wave frequency in ALS patients is15.2±11.6month, and that in CSM patients is35.0±37.0month. The shortest disease duration of ALS patient who have a low F-wave frequency is only2month, and that in CSM patients is12month. The mean disease duration of prolonged F-wave latency in ALS patients is15.0±14.2month, and the shortest of that is4month. But only one patient of CSM had a prolonged F-wave latency.Conclusion:Patients of ALS had a F-wave conduction feature of lower F-wave frequency, prolonged F-wave mean latency and increased F-wave dispersion. They had a strong correlation with muscle strength. But F-wave velocity only changed a little.They also had a motor nerve conduction feature of prolonged DML and lower CMAP amplitude. We found a high correlation between CMAP amplitude and both atrophy of muscle and strength as assessed by the MRC scale, but there was no correlation between CMAP amplitude and both pyramidal sign and disease duration. Split hands and split legs were exist in the ALS patients.A very few patients had a abnormal sensory nerve conduction and it always happened in the advanced stage of disease. Compared with CSM patients, ALS patients had a obviously prolonged DML,lower CMAP amplitude, lower F-wave frequency, slow F-wave velocity and prolonged F-wave mean latency. So we considerd CMAP amplitude could be a parameter for differential diagnosis of these two diseases. But the male female ratio, disease duration and pyramidal sign between this two groups did not have a significant different.The disease duration of ALS who had a low F-wave frequency or prolonged F-wave latency is much earlier than that of CSM.So the diagnosis of ALS should be considered if the patient had a low F-wave frequency or prolonged F-wave latency in the beginning of the disease or within6month.