Critical illness myopathy: further evidence from muscle-fiber excitability studies of an acquired channelopathy

Recent studies have demonstrated acquired muscle inexcitability in critical illness myopathy (CIM) and have used direct muscle stimulation (DMS) techniques to distinguish neuropathy from myopathy as a cause of weakness in the critically ill. The mechanisms underlying weakness in CIM are incompletely understood and DMS is only semiquantitative. We report results from a series of 32 patients with CIM and demonstrate significant slowing of muscle-fiber conduction velocity (MFCV) and muscle-fiber conduction block during the acute phase of CIM, which correlates with prolonged compound muscle action potential (CMAP) duration, clinical severity, and course. We also used a paired stimulation technique to explore the excitability of individual muscle fibers in vivo. We demonstrate altered muscle-fiber excitability in CIM patients. Serial studies help define the course of these pathophysiological changes. Parallels are made between CIM and hypokalemic periodic paralysis. Our findings provide further evidence for muscle membrane dysfunction being the principal underlying abnormality in CIM.     

危重病性多发性神经肌病电生理特点及对机械通气的影响

目的 浅析危重病性多发性神经肌病(CIPM)的电生理特点及对机械通气支持时间的影响.方法 应用丹麦Keypoint 4肌电图仪对重症监护病房中17例机械通气时间>1周仍未能脱机的肺部感染致呼吸衰竭患者进行神经电生理检测,观察其电生理特点并比较CIPM与非CIPM患者的机械通气时间.结果 17例患者中CIPM 9例,其中亚型危重病性多发性神经病(CIP)6例,危重病性肌病(CIM)3例.CIPM患者均表现四肢交感神经皮肤反应(SSR)异常和复合肌肉动作电位(CMAP)下降,CIP患者伴有感觉神经动作电位(SNAP)波幅减低而神经传导速度(NCV)正常.除2例CIP和2例CIM患者F波出现率减低外,全部CIPM患者重复神经电刺激、体感诱发电位及瞬目反射检测均正常.CIPM患者机械通气时间中位数(四分位数范围)为30.0 d(20.0～45.0 d),比非CIPM患者13.5 d(9.5～17.5 d)明显延长(U=7.500,P=0.006).结论 CIPM患者主要表现为CMAP和(或)SNAP波幅的减低,而NCV正常,全部患者SSR异常且脱机时间延长.     

Early detection of evolving critical illness myopathy with muscle velocity recovery cycles

ObjectiveTo investigate the sensitivity of muscle velocity recovery cycles (MVRCs) for detecting altered membrane properties in critically ill patients, and to compare this to conventional nerve conduction studies (NCS) and quantitative electromyography (qEMG).MethodsTwenty-four patients with intensive care unit acquired weakness (ICUAW) and 34 healthy subjects were prospectively recruited. In addition to NCS (median, ulnar, peroneal, tibial and sural nerves) and qEMG (biceps brachii, vastus medialis and anterior tibial muscles), MVRCs with frequency ramp were recorded from anterior tibial muscle.ResultsMVRC and frequency ramp parameters showed abnormal muscle fiber membrane properties with up to 100% sensitivity and specificity. qEMG showed myopathy in 15 patients (63%) while polyneuropathy was seen in 3 (13%). Decreased compound muscle action potential (CMAP) amplitude (up to 58%) and absent F-waves (up to 75%) were frequent, but long duration CMAPs were only seen in one patient with severe myopathy.ConclusionsAltered muscle fiber membrane properties can be detected in patients with ICUAW not yet fulfilling diagnostic criteria for critical illness myopathy (CIM). MVRCs may therefore serve as a tool for early detection of evolving CIM.SignificanceCIM is often under-recognized by intensivists, and large-scale longitudinal studies are needed to determine its incidence and pathogenesis.     

Symmetry of phrenic nerve motor response in amyotrophic lateral sclerosis

To test for interside differences and ipsilateral correlation of compound muscle action potentials (CMAP) from muscles of the cervical region according to El Escorial criteria, we stimulated the phrenic, axillary, and ulnar nerves bilaterally in 67 patients with amyotrophic lateral sclerosis. The diaphragm CMAP was symmetric, but it did not correlate with deltoid or abductor digiti minimi (ADM) CMAPs. The deltoid CMAP in all groups and ADM CMAP in bulbar- and lower-limb-onset patients showed significant interside correlation. The ADM CMAP is asymmetric in upper-limb-onset patients. Unilateral stimulation is sufficient to monitor the phrenic nerve response; its degree of CMAP decrease does not correlate with other cervical muscle involvement.     

低钾型周期性瘫痪患者运动诱发试验中肌力和肌电图改变与血钾的关系

目的 通过长时运动诱发试验,观察低钾型周期性瘫痪患者肌力和肌电图的变化与血钾之间的关系.方法 收集确诊为低钾型周期性瘫痪患者78例,对小指展肌进行运动诱发试验测定,以拇短展肌作为对照,观察120 min,测定运动诱发前后尺神经/小指展肌和正中神经/拇短展肌复合肌肉动作电位(compound muscle action potential,CMAP)波幅变化,同时观察患者小指外展和小指内收肌力以及拇短展肌肌力的变化,部分患者测定运动前后血钾水平.分析运动后不同肌肉的肌力、CMAP波幅与血钾之间的关系.结果 在小指外展运动后,78例患者尺神经CMAP波幅运动后比运动前明显下降,分别为(4.6±2.7)、(9.6±3.2)mV(t=16.047,P=0.000),而正中神经CMAP波幅在小指外展运动后与运动前相比无明显差异,分别为(10.9±4.2)、(11.2±3.9)mV(t=0.673,P=0.822).在运动后,76例小指外展肌力下降;有41例小指外展肌力小于Ⅲ级,但同侧小指内收和拇短展肌肌力仍为V级,对其中10例患者在运动前和运动后测定血钾,结果无明显差异,分别为(3.8±0.3)、(3.9±0.4)mmol/L(t =0.395,P=0.702).结论 在低钾型周期性瘫痪患者进行运动诱发试验时,血钾并非影响肌力和CMAP波幅变化的关键因素.     

Correlation between distal motor latency and compound muscle action potential in amyotrophic lateral sclerosis

OBJECTIVES: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder, characterized by a selective progressive degeneration of the motor system. Electromyography is essential for the diagnosis of ALS. The measurement of motor conduction of peripheral nerves is of major importance to recognize other possible causes of progressive muscle wasting. However, there are also pathologic changes in nerve conduction studies in ALS patients. METHODS: In this study we analysed the values of distal motor latency (DML), compound muscle action potential (CMAP) and motor nerve conduction velocity (MNCV) in 95 patients with definite ALS. RESULTS: We found slight slowing of MNCV and moderate to strong reduction of CMAP and a prolongation of DML. We found no significant correlation between MNCV and CMAP. DISCUSSION: The main finding of the present work was the negative correlation between DML and CMAP. It is interpreted as a very distal axonal damage as the main reason for prolongation of DML in ALS patients.     

91例肌萎缩侧索硬化症的F波和神经传导研究

目的探讨肌萎缩侧索硬化症(ALS)F波和神经传导改变的特点.方法所有患者均采用常规方法测定感觉神经传导速度(SCV)、运动末端潜伏期(distal motor latency,DML)和F波,后者的测定包括潜伏期和/或传导速度及出现率.分析了DML和复合肌肉动作电位(compound muscle action potential,CMAP)波幅、F波出现率与肌力的关系.结果在91例ALS患者中,仅有3例SCV异常;正中神经、尺神经及胫后神经DML延长者分别占16.7%、13.8%、7.1%,CMAP波幅下降者分别占50.0%、44.6%、28.6%;5.0%患者F波传导速度异常,48例患者F波出现率下降,其中19例出现率为0.肌力下降者DML、CMAP波幅及F波出现率改变明显.结论ALS患者可出现DML延长和CMAP波幅降低,二者比较后者的改变更显著;F波传导速度相对正常而出现率下降明显;DML、CMAP波幅及F波出现率的异常与肌力明显相关(P均＜0.01).     

Intraoperative oculomotor nerve monitoring predicts outcome following clipping of posterior communicating artery aneurysms

Valid parameters do not exist to predict oculomotor nerve palsy (ONP, ptosis and/or diplopia) intraoperatively. In 49 operations involving 46 patients with posterior communicating artery aneurysms, the oculomotor nerves were stimulated after the aneurysms were clipped. A quantitative analysis of evoked compound muscle action potential (CMAP) parameters (stimulus threshold, amplitude and latency) from the levator palpebrae superioris (LPS) muscle was performed. Absolute values of CMAP amplitude statistically correlated with initial and long-term oculomotor nerve function (ONF) after surgery (p<0.05). In addition, subarachnoid hemorrhage (SAH) significantly influenced the CMAP threshold (p<0.05). Monitoring of LPS muscle activity is valuable in the assessment of ONF, and the CMAP amplitude of LPS may be a reliable predictor of ONF. Moreover, SAH has an impact on the parameters of the LPS CMAP.     

肌萎缩侧索硬化患者复合肌肉动作电位特点分析及其与临床关系的研究

目的分析肌萎缩侧索硬化患者复合肌肉动作电位之特点,探讨波幅改变与肌力、病程以及神经功能等级评分等方面的关系。方法收集2001年5月-2004年11月肌电图检查表现为广泛神经源性损害的肌萎缩侧索硬化患者127例,根据ElEscorial诊断标准,确诊级43例、拟诊级39例、可能级13例、可疑级32例。选择其中确诊级和拟诊级患者82例进行神经功能评分和Appel肌萎缩侧索硬化量表评分,然后对其复合肌肉动作电位波幅值与肌力、病程以及神经功能评分变化间的关系进行比较分析。结果(1)82例患者复合肌肉动作电位波幅下降,与肌力改变呈明显指数拟合关系(r=0.969,P=0.001)。(2)同一患者波幅水平随病程而逐渐降低,波幅下降速度较慢者病程较长;不同患者的波幅与病程无显著相关(r=!0.077,P=0.502)。(3)复合肌肉动作电位波幅水平降低与神经功能等级评分呈显著正相关(r=0.412,P=0.001),与Appel评分呈显著负相关(r=!0.549,P=0.001)。(4)患者复合肌肉动作电位波幅水平的降低与运动神经传导速度无明显相关(r=!0.087,P=0.545),但若将波幅与传导速度转换为正常下限的百分比取其平方根后,二者间则呈线性相关(r=0.382,P<0.001)。结论复合肌肉动作电位波幅改变是肌萎缩侧索硬化原发性与继发性病理改变共同作用的结果,随着患者肌无力和肌萎缩症状的逐渐加重,复合肌肉动作电位波幅亦明显下降,但由于此时髓鞘仍保留完整,传导速度仍可保持正常,提示肌萎缩侧索硬化患者肌力下降的机制主要系下运动神经元损害所致。在同一患者,复查时显示复合肌肉动作电位波幅随病程进展而逐渐下降,但尚难建立反映二者平行关系的时间-波幅曲线,提示复合肌肉动作电位波幅改变与病程关系较为复杂。此外,复合肌肉动作电位波幅与肌萎缩侧索硬化患者的神经功能等级评分和Appel量表评分明显相关,提示早期波幅下降较慢者病情相对较轻。     

肌萎缩侧索硬化患者205例的神经传导特点分析

目的 分析肌萎缩侧索硬化(ALS)患者的神经传导和F波特点,并探讨其与肌力、病程和首发部位等之间的关系.方法 收集于1997年1月至2008年5月期间我院门诊或病房收治的ALS患者205例,均采用常规肌电图检查,测定其运动神经传导、F波以及感觉神经传导(SCV).结果 在205例ALS患者中,仅有3例SCV异常,正中神经、尺神经及胫后神经末端潜伏期(DML)延长者分别占24.9%(48/193)、15.3%(25/163)、21.2%(7/33),复合肌肉动作电位(CMAP)波幅下降者分别占57.0%(110/193)、49.7%(81/163)、39.4%(13/33);68.9%(122/177)患者F波出现率下降,其中31.1%(55/177)F波出现率为0,肌力下降者DML、CMAP波幅及F波出现率改变明显.肢体起病组正中神经CMAP波幅下降[81.5%(53/65)]和F波异常率[70.9%(44/62)出现率下降,45.1%(28/62)出现率为0]较延髓部起病者[32.4%(11/34);F波38.2%(13/34)出现率下降,14.7%(5/34)出现率为0]更明显,两组比较差异有统计学意义(x2=23.629、9.753、9.029,均P<0.01);DML异常两组间差异无统计学意义.Logistic回归分析显示CMAP波幅的降低与上肢远端肌力、首发部位、病程显著相关,F波出现率的降低与上肢远端肌力、首发部位相关.结论 ALS患者可出现DML延长和CMAP波幅降低(后者改变更显著),F波出现率明显下降而传导速度相对正常;DML、CMAP波幅及F波出现率的异常与肌力明显相关.首发部位为肢体和(或)上肢远端肌力下降者CMAP波幅及F波异常率更明显.

Abstract：

Objective To investigate the F-wave and nerve conduction in patients with amyotrophic lateral sclerosis (ALS) and explore the correlation between these parameters and muscle strength, disease duration and onset site.Methods The data of outpatients and inpatients diagnosed with ALS were collected in Peking Union Medical College Hospital from January 1997 to May 2008.Standard sensory and motor nerve conduction study of the median nerve, ulnar nerve and tibial nerve was performed in 205 patients with ALS.F-wave velocity and frequency was measured in median nerve.Parameters for analyses included sensory conduction velocity and amplitude, distal motor latency (DML), and compound muscle action potential (CMAP) amplitude.Correlation between muscle strength and DML, CMAP amplitude or F-wave frequency were also explored.Results Delayed DML of the median nerve, ulnar nerve and tibial nerve were found in 24.9% (48/193), 15.3% (25/163), 21.2% (7/33) of patients respectively.Decreased CMAP amplitudes were found in 57.0% (110/193), 49.7% (81/163), 39.4% (13/33) of patients respectively.Decreased F-wave frequency of the median nerve was found in 68.9% (122/177) of patients.The abnormality of DML,CMAP amplitude and F-wave frequency of median nerve were increased in weaker muscles.Decreased median nerve CMAP amplitude (81.5% (53/65)) and F-wave abnormality (decreased persistence 70.9%(44/62), absent responses 45.1% (28/62)) in spinal onset groups were significantly higher than those in bulbar onset groups (CMAP 32.4% (11/34); F-wave: decreased persistence 38.2% (13/34), absent responses 14.7% (5/34); x2 = 23.629, 9.753, 9.029,all P <0.01).Compared with the bulbar onset group,the abnormality of DML in spinal onset group was higher, but not reach statistical significance.Logistic regression revealed a strong direct association between decreased CMAP amplitudes and upperextremity muscles strength, disease duration and onset symptom.Abnormality of F-wave frequency was associated with upper-extremity muscles strength and onset symptom.Conclusions Delayed DML and decreased amplitude of CMAP are found in ALS patients.CMAP amplitude is a sensitive parameter related to the severity of ALS.F-wave velocity is relatively normal while F-wave frequency of the median nerve is correlated with muscle strength.Decreasing CMAP amplitude and F-wave frequency are correlated strongly with muscle weakening,disease duration and symptom onset over limbs.     

Critical illness polyneuropathy and myopathy: a major cause of muscle weakness and paralysis

Critical illness polyneuropathy (CIP) and myopathy (CIM) are complications of critical illness that present with muscle weakness and failure to wean from the ventilator. In addition to prolonging mechanical ventilation and hospitalisation, CIP and CIM increase hospital mortality in patients who are critically ill and cause chronic disability in survivors of critical illness. Structural changes associated with CIP and CIM include axonal nerve degeneration, muscle myosin loss, and muscle necrosis. Functional changes can cause electrical inexcitability of nerves and muscles with reversible muscle weakness. Microvascular changes and cytopathic hypoxia might disrupt energy supply and use. An acquired sodium channelopathy causing reduced muscle membrane and nerve excitability is a possible unifying mechanism underlying CIP and CIM. The diagnosis of CIP, CIM, or combined CIP and CIM relies on clinical, electrophysiological, and muscle biopsy investigations. Control of hyperglycaemia might reduce the severity of these complications of critical illness, and early rehabilitation in the intensive care unit might improve the functional recovery and independence of patients.     

Anterior tibialis cmap amplitude correlations with impairment in CMT1A

Introduction: CMT1A is the most common form of Charcot‐Marie‐Tooth disease (CMT), a slowly progressive neuropathy in which impairment is length dependent. Fibular nerve conduction studies to the anterior tibialis muscle (AT) may serve as a physiological marker of disease progression in patients with CMT1A. The objective of this study is to determine whether the AT compound muscle action potential (CMAP) amplitude correlates with impairment in patients with CMT1A. Methods: We correlated AT CMAP amplitudes and impairment measured by the CMT Neuropathy Score (CMTNS) in a cross‐section of 121 patients with CMT1A and a subset of 27 patients with longitudinal data. Results: AT CMAP amplitudes correlated with impairment as measured by the CMTNS in cross sectional analysis. Longitudinal changes in the AT CMAP showed a strong inverse correlation with leg strength but not other components of the CMTNS. Conclusions: AT CMAP amplitude may serve as a useful outcome measure for physiological changes in natural history studies and clinical trials for patients with CMT1A. Muscle Nerve, 2013     

Supratentorial ischemic stroke: more than an upper motor neuron disorder.

The primary goal of this study was to identify secondary functional changes in the peripheral motor units of the paretic upper extremity (UE) in patients with severe ischemic stroke and to determine how these changes develop during the first weeks after stroke. An inception cohort of 27 consecutive patients with an acute ischemic supratentorial stroke and an initial UE paralysis was compared with 10 healthy control subjects. The ulnar nerve was electrically stimulated proximal to the wrist and electromyographic recordings were obtained from the abductor digiti minimi muscle. Hemiparetic side mean values of the compound muscle action potential (CMAP) 1 and 3 weeks after stroke were compared with the nonparetic side and with CMAP values obtained from healthy control subjects. The mean CMAP amplitude in patients was significantly lower on the paretic side compared with the nonparetic side and with control subjects. Decrease in CMAP amplitude was observed in more than half of the stroke patients, sometimes as early as 4 days after stroke, and persisted in most cases. Whenever present, it was accompanied by absence of motor recovery at that specific time after stroke. Decreased CMAP amplitude in the abductor digiti minimi muscle can be seen already in the very acute phases after stroke unrelated to peripheral neuropathy, radiculopathy, or plexopathy, and it is accompanied by absence of UMN recovery. This knowledge is important for interpreting electrophysiological data in stroke patients.     

Peripheral motor nerve conduction abnormality,muscle strength,and muscle wasting in patients with acute stroke: A pilot study

IntroductionStroke-related muscle wasting are important therapeutic targets to reduce disability in patients with stroke. Peripheral nerve conduction impairment is one reported factor that causes muscle wasting in these patients, but muscle strength, muscle wasting, and peripheral nerve conduction abnormality have not been examined in patients with acute stroke. We therefore investigated changes in lower-leg motor nerve conduction, muscle strength, and muscle wasting in patients with acute stroke.MethodsPatients with acute stroke were recruited. Their motor conduction velocity (MCV) and compound motor action potential (CMAP) amplitude in both sides of the common peroneal nerve, and lower paretic leg muscle strength by the Motricity Index (MI) and quadriceps muscle thickness (QMT) on both sides were measured at the time of admission and again 2 weeks later.ResultsEighteen patients with acute stroke (median [interquartile range], age = 68 [14] years; female = 4 [22%]) were enrolled. The MCV and CMAP amplitude were not significantly different between limbs. The QMT was significantly reduced in paretic (P = 0.014) and non-paretic (P = 0.003) limbs, but the lower paretic leg MI was increased (P = 0.0.001). There was a significant correlation between % differences in CMAP amplitude and % differences in QMT in the paretic limb (R = 0.604, P = 0.008), but not in the non-paretic limb (R = 0.225, P = 0.369).ConclusionsLower-leg muscle wasting was associated with the change in CMAP amplitude in paretic limbs, but not in non-paretic limbs, in patients with acute stroke.     

Electrophysiological features of Hirayama disease

Introduction: The purpose of this study was to compare the pattern of hand muscle involvement in Hirayama disease (HD) and amyotrophic lateral sclerosis (ALS). Methods: We reviewed findings of upper limb nerve conduction studies of 46 HD patients and 60 ALS patients. The findings from 54 healthy subjects were used for comparison. Results: In HD, the ulnar compound muscle action potential (CMAP) amplitude was more severely reduced than the median one, and the reverse pattern was observed in ALS. The mean ulnar/median (U/M) CMAP amplitude ratio was significantly lower in HD (0.64 ± 0.79) and abnormally higher in ALS (2.15 ± 1.77) compared with normal subjects (0.89 ± 0.23). An abnormally low U/M CMAP amplitude ratio (<0.6) was encountered in 34 patients with HD and in 1 with ALS. A U/M CMAP amplitude ratio ≥4.5 or absent median motor response was found only in ALS. Conclusion: Our findings demonstrate different patterns of hand muscle involvement between these two diseases. Muscle Nerve, 2011     

Motor unit number index (MUNIX): principle, method, and findings in healthy subjects and in patients with motor neuron disease

The motor unit number index (MUNIX) is a method for assessment of number and size (MUSIX) of motor units (MUs) using the compound muscle action potential (CMAP) and surface electromyographic interference pattern (SIP). This method was used to study the hypothenar muscle in 34 healthy subjects to define normal range, and to study reproducibility. Four healthy subjects and 13 patients with amyotrophic lateral sclerosis (ALS) were studied serially over a 1-year period. In healthy subjects, MUNIX showed good reproducibility. In serial studies, healthy subjects showed no change in the CMAP amplitude and MUNIX. ALS patients with minimal change in CMAP amplitude had a significant drop in MUNIX and increase in MUSIX, indicating MU loss compensated by reinnervation. When the CMAP changed significantly (>30%) in 1 year, the CMAP and MUNIX decreased in parallel. MUNIX would be useful to study MU loss in degenerative diseases of motor neurons. Muscle Nerve 42: 798-807, 2010.     

Lack of cold sensitivity in hyperkalemic periodic paralysis

The nosologic distinction between paramyotonia congenita and hyperkalemic periodic paralysis is somewhat blurred. Muscle membrane inexcitability induced by cooling seems to be characteristic of paramyotonia congenita. The effect of cooling on the maximal compound muscle action potential (CMAP) in patients with paramyotonia congenita was compared to that in patients with hyperkalemic periodic paralysis. Diminution in CMAP amplitude and area, which was observed in paramyotonia congenita, did not occur in hyperkalemic periodic paralysis. We suggest that this effect of cooling on the CMAP can be utilized in the differentiation of these two syndromes.     

Responsiveness to botulinum toxin type A in muscles of complex regional pain patients with tonic dystonia

Tonic dystonia of the limbs in complex regional pain syndrome (CRPS) is associated with considerable disability. Treatment options are scarce. Botulinum toxin (BoNT) is sometimes used, but the effect is often said to be disappointing. However, this notion stems from case reports and clinicians’ opinions but has never been formally studied. We therefore investigated responsiveness to BoNT in CRPS patients with tonic dystonia. We injected the extensor digitorum brevis (EDB) muscle with BoNT-A in 17 patients with CRPS and tonic dystonia to compare the response between affected and unaffected legs. We also investigated the right legs of 17 healthy controls. Responsiveness was defined as a decrease of the amplitude of the compound muscle action potential (CMAP) of >20 % from baseline 2 weeks after BoNT-A injection. We controlled for a temperature effect on BoNT efficacy by measuring skin temperature hourly directly above the EDB muscle in the first 2 weeks. CMAP amplitude decreased >20 % after injection on the affected side in 16 of 17 CRPS patients, similar to the response in unaffected legs (12/13) or legs of controls (17/17). The degree of CMAP reduction was significantly smaller in patients than in controls (56.0 ± 22.3 vs. 70.6 ± 14.6 %; p = 0.031). This may be due to a lower physical activity level and a greater difficulty to localize the EDB muscle properly in affected legs. The decrease in CMAP amplitude was not related to skin temperature. Contrary to the prevailing opinion, BoNT-A has a normal, although perhaps slightly lower efficacy in CRPS patients with dystonia.     

Reply to Spielholz

In this study we describe the electrophysiological findings in botulism patients with neuromuscular respiratory failure from major botulism outbreaks in Thailand. High‐rate repetitive nerve stimulation testing (RNST) of the abductor digiti minimi (ADM) muscle of 17 botulism patients with neuromuscular respiratory failure showed mostly incremental responses, especially in response to >20‐HZ stimulation. In the most severe stage of neuromuscular respiratory failure, RNST failed to elicit a compound muscle action potential (CMAP) of the ADM muscle. In the moderately severe stage, the initial CMAPs were of very low amplitude, and a 3‐HZ RNST elicited incremental or decremental responses. A 10‐HZ RNST elicited mainly decremental responses. In the early recovery stage, the initial CMAP amplitudes of the ADM muscle improved, with initially low amplitudes and an incremental response to 3‐ and 10‐HZ RNSTs. Improved electrophysiological patterns of the ADM muscle correlated with improved respiratory muscle function. Incremental responses to 20‐HZ RNST were most useful for diagnosis. The initial electrodiagnostic sign of recovery following treatment of neuromuscular respiratory failure was an increased CMAP amplitude and an incremental response to 10–20‐HZ RNST. Muscle Nerve 40: 271–278, 2009     

A new method to measure the distribution of motor conduction velocity in man.

A new method of measuring the distribution of conduction velocities in human motor fibers is described. In this method, a modification of Kimura's collision technique is combined with Hopf's technique. This enabled us to determine the collision end-point in Hopf's technique, from which the minimum velocity is derived. The size of the distorted compound muscle action potential (CMAP) measured with Hopf's technique is corrected using the CMAP size with the modified Kimura technique. This resolves the problem of CMAP distortion due to transient change in muscle conduction in Hopf's technique. In addition, a new equation to correct for the refractory period was developed. This can be applied even if there is stimulus spread. Using our method, one can clearly determine the maximum and minimum velocities. The former corresponds to the motor conduction velocity as measured by the conventional method.