Origin of ICU acquired paresis determined by direct muscle stimulation

BACKGROUND: Acquired diffuse paresis in an intensive care unit (ICU) can result from critical illness myopathy or polyneuropathy. Clinical examination and conventional neurophysiological techniques may not distinguish between these entities. OBJECTIVE: To assess the value of direct muscle stimulation (DMS) to differentiate myopathic from neuropathic process in critically ill patients with diffuse severe muscle weakness. METHODS: 30 consecutive patients with ICU acquired diffuse motor weakness were studied. Responses of the right deltoid and tibialis anterior muscles to DMS and to motor nerve stimulation (MNS) were studied and compared with results of conventional nerve conduction studies and concentric needle electromyography (EMG). An original algorithm was used for differential diagnosis, taking into account first the amplitude of the responses to DMS, then the MNS to DMS amplitude ratio, and finally the amplitude of the sensory nerve action potentials recorded at the lower limbs. RESULTS: Evidence of neuropathy and myopathy was found in 57% and 83% of the patients, respectively. Pure or predominant myopathy was found in 19 patients. Other results were consistent with neuromyopathy (n = 5) and pure or predominant neuropathy (n = 2). Four patients had normal results with stimulation techniques, but spontaneous EMG activity and raised plasma creatine kinase suggesting necrotic myopathy. CONCLUSIONS: A neurophysiological approach combining DMS and conventional techniques revealed myopathic processes in a majority of ICU patients. Reduced muscle fibre excitability may be a leading cause for this. The diagnosis of myopathy in ICU acquired paralysis can be established by a combination of DMS, needle EMG, and plasma creatine kinase.     

Approach to neuromuscular disorders in the intensive care unit

Neuromuscular disorders increasingly are recognized as a complication in patients in the intensive care unit (ICU) and represent a common cause of prolonged ventilator dependency. The distinct syndromes of critical illness myopathy, prolonged neuromuscular blockade, and critical illness polyneuropathy (CIP) may arise as a consequence of sepsis, multi-organ failure, and exposure to various medications—notably, intravenous corticosteroids and neuromuscular blocking agents—but the pathophysiology of these disorders remains poorly understood. More than one syndrome may occur simultaneously, and the distinctions may be difficult in a particular patient, but a specific diagnosis usually can be established after careful clinical, electrodiagnostic, and, when necessary, histological evaluation. For example, asthmatics requiring treatment with corticosteroids and neuromuscular blocking agents may develop an acute myopathy characterized by generalized weakness, preserved eye movements, elevated creatine kinase levels, and myopathic motor units on electromyography (EMG). Muscle biopsy demonstrates distinctive features of thick (myosin) filament loss on ultrastructural studies. Conversely, those with a prolonged ICU course that is complicated by episodes of sepsis with failure to wean from the ventilator, distal or generalized flaccid limb weakness, and areflexia probably have CIP. EMG in these patients demonstrates reduced or absent motor and sensory potentials with neurogenic motor units. Prolonged neuromuscular blockade most commonly occurs in patients with renal failure who have received prolonged infusions of neuromuscular blockers. There is severe flaccid, areflexic paralysis with normal sensation, facial weakness, and ophthalmoparesis that persists for days or weeks after the neuromuscular blockers have been discontinued. Repetitive nerve stimulation shows a decrement of the compound muscle action potential and, in most cases, establishes a disorder of neuromuscular transmission. With the recent epidemic of West Nile virus infection, a clinical syndrome of acute flaccid paralysis with several features indistinguishable from poliomyelitis has emerged. This article critically examines the clinical, electrophysiological, and pathological features of these and other acute neuromuscular syndromes that arise in the context of ICU care and summarizes the current understanding of the pathophysiology and treatment of these disorders.     

Assessing neuromuscular disease with multifrequency electrical impedance myography

Electrical impedance myography (EIM) is a noninvasive technique for neuromuscular assessment in which low-intensity alternating current is applied to a muscle and the consequent surface voltage patterns are evaluated. Previous work using a single frequency of 50 kHZ has demonstrated quantitative correlation of EIM parameters with disease status. In this investigation we examined the use of multifrequency EIM, studying a prototypical neurogenic disease (amyotrophic lateral sclerosis, ALS) and myopathic disorder (inflammatory myopathy, IM). Eleven ALS patients, 7 IM patients, and 46 normal subjects participated in the study. Although disease-specific patterns were not identified such that IM could be differentiated from ALS, impedance vs. frequency patterns for diseased subjects differed substantially from those of the age-matched normal subjects, with the greatest alterations occurring in the most severe cases. Multifrequency EIM may be well-suited to serve as an easily applied technique to assess disease severity in a variety of neuromuscular conditions.     

A Comparison of EMG and Muscle Biopsy in ICU Weakness

Background  

Patients can become weak in ICU from various etiologies and mechanisms. Establishing the diagnosis is invaluable for prognostic determination and specific management. We evaluated the relative contributions of clinical, laboratory, electomyographic studies (EMG), and percutaneous muscle biopsy (MB) in determining the cause of muscular weakness that developed in a series of patients while in ICU. The principal objective is to determine the concordance between results of the EMG and MB studies in patients with ICU-acquired weakness.     

ICU获得性肌无力的研究进展

很多急危重症或经历复杂手术的患者往往需要入住重症监护病房（ICU）治疗,以期平稳度过危险期。其中,部分患者因多种原因而出现不同程度的肢体无力、呼吸肌力量减弱、深反射减弱等症状,对此现象国外学者提出了ICU获得性肌无力（IUCAW）的概念。据报道ICUAW诊断困难、恢复缓慢是导致患者撤机困难、住院时间延长的主要原因之一,对急危重症患者的预后产生了巨大的影响,从社会经济学角度而言也造成了医疗资源的过度消耗。随着电生理学及各种诊断方法的进展,在ICUAW的发病机制及治疗措施等方面均取得了长足的进步。本文将围绕ICUAW的定义及分类、基本特征、病理生理机制、诊断及防治进行概述。     

Diagnostic accuracy of clinical data, quantitative electromyography and histochemistry in neuromuscular disease. A study of 105 cases

One hundred and five (105) cases of muscle weakness were reviewed in order to evaluate the reliability of clinical diagnosis, quantitative EMG, and muscle histochemistry in neuromuscular disorders. Patients were grouped into 3 categories: group I, disorders which could be diagnosed by clinical observation alone (38 patients); group II, disorders in which the EMG and biopsy were necessary for delineation (63 patients); disorders in which it was not possible to make a diagnosis because the clinical and laboratory studies were contradictory (4 patients). In group I, only one patient showed an inconsistency between clinical and laboratory data. In group II, the EMG and biopsy were concordant in all but 4 cases of Kugelberg-Welander syndrome with neuropathic EMG and myopathic biopsy. In group III, 4 patients had a myopathic EMG and neuropathic biopsy.The overall concordance of EMG and histochemistry was greater than 90%. The laboratory studies also discerned 2 different categories of disease, “neuropathic” and “myopathic”. The consistency in EMG and histochemistry correlation suggests that a true division between neuropathic and myopathic disorders exists.     

Discriminating neurogenic from myopathic disease via measurement of muscle anisotropy

Skeletal muscle is electrically anisotropic, with a tendency for applied electrical current to flow more readily along muscle fibers than across them. In this study, we assessed a method for non‐invasive measurement of anisotropy to determine its potential to serve as a new technique for distinguishing neurogenic from myopathic disease. Measurements were made on the biceps brachii and tibialis anterior muscles in 15 normal subjects and 12 patients with neuromuscular disease (6 with amyotrophic lateral sclerosis and 6 with various myopathies) using 50 kHZ applied current. Consistent multi‐angle anisotropic patterns were found for reactance and phase in both muscles in normal subjects. Normalized anisotropy differences for each subject were defined, and group average values identified. The amyotrophic lateral sclerosis (ALS) patients demonstrated increased and distorted anisotropy patterns, whereas myopathic patients demonstrated normal or reduced anisotropy. These results suggest that non‐invasive measurement of muscle anisotropy has potential for diagnosis of neuromuscular diseases. © 2008 Wiley Periodicals, Inc. Muscle Nerve, 2009     

Halothane-caffeine contracture testing in neuromuscular diseases

The association of malignant hyperthermia (MH) with neuromuscular disorders has been recognized since 1970. These disorders include central core disease, Duchenne muscular dystrophy, myotonia congenita, myotonic dystrophy, nonspecific myopathies, and King-Denborough syndrome. In order to assess the anesthetic risk of MH in the neuromuscular population, we performed halothane and caffeine contracture testing for MH susceptibility on biopsied muscle removed from 25 consecutive neuromuscular patients during diagnostic evaluation. Positive contracture tests were found in 7 of 18 patients with myopathic disorders and 3 of 7 patients with neurogenic disorders. Two of our patients had anesthetic events suggesting MH. These findings suggest that myopathic and neuropathic disorders share pathogenic mechanisms with MH, resulting in positive contracture tests and possibly leading to clinical events during anesthesia. Although there is controversy regarding the interpretation of a positive contracture test, contracture testing remains the most widely accepted test for MH susceptibility. Thus, a variety of neuromuscular disorders may be associated with MH susceptibility, and caution should be exercised during anesthesia in this group of patients.     

Electromyographic evidence of subclinical myopathy in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is due to a number of mutations of contractile protein genes such as beta-cardiac myosin, myosin binding protein-C, and troponin-T. Unlike troponin-T, beta-myosin is a constituent of slow skeletal muscle and its mutations generally have a better prognosis. In order to investigate the usefulness of electromyography in detecting skeletal muscle involvement in HCM, 46 patients were examined using both conventional electromyography (EMG) and quantitative electromyography (QEMG) methods. The QEMG involved motor unit potential (MUP) analysis, turns/amplitude (TAA) analysis, and power spectrum analysis of the interference pattern. Using conventional EMG, myopathic findings were demonstrated in 13 patients (28%). Receiver operating characteristic (ROC) analysis of the results of a discriminant function extracted using QEMG values, identified correctly 10 out of 11 normal controls and all 9 myopathic control patients, and displayed a 15% presence of myopathy (7 patients) among the cardiomyopathy group. The duration of MUPs was the most sensitive among the quantitative parameters in differentiating normal from myopathic subjects. Since skeletal muscle involvement may be due to distinct gene mutations, normal and myopathic EMG findings may reflect HCM subpopulations with a different genetic substrate.     

CT-scanning of skeletal muscle in arthrogryposis multiplex congenita

CT-scanning of skeletal muscles was performed on 14 patients with arthrogryposis multiplex congenita (AMC), according to an eight-slice protocol. Adipose tissue replacement and atrophy of muscles was found in six patients with neurogenic or myopathic origin of AMC, associated with severe muscle weakness. In the remaining patients with other forms of AMC, in which muscle weakness was less marked or absent, muscular CT-scanning was normal. It is stated that muscular CT-scanning is not a routine investigation in a screening procedure of all cases of AMC. However, CT-scanning appears to be useful in cases of severe AMC with associated muscle weakness in detecting the neurogenic and myopathic forms. It also facilitates the selection of a suitable site for EMG and biopsy and may provide important information for orthopaedic management.     

Muscle fibre type composition in distal myopathy (Welander). An analysis with enzyme- and immuno-histochemical, gel-electrophoretic and ultrastructural techniques

The myopathic muscle of distal myopathy (Welander's disease), the dominantly inherited neuromuscular disorder which occurs frequently in Sweden, has been characterized by electron microscopy, enzyme- and immuno-histochemistry (using antibodies against embryonic, neonatal, fast and slow myosin, and against the muscle-specific intermediate filament protein, desmin), and with gel electrophoretic techniques. Of special interest is the fact that the ultrastructural appearance of the fibres with regard to M- and Z-band structures does not fit the proposed classification criteria for ultrastructural fibre typing of normal human muscle. Furthermore, contrary to previous results, we conclusively demonstrate that the predominating fibres are of a slow-twitch type. Unexpectedly, we also observed that embryonic and neonatal myosin was expressed in some residual fibres. This emphasises the importance of supplementing stains to demonstrate activity of ATPase with myosin immuno-histochemistry in order to improve understanding of fibre type characteristics in myopathic muscles. The origin of the myopathic muscle fibres in distal myopathy could not be definitely determined, but it is suggested that neurogenic disturbances play an important part in the pathophysiology of Welander's disease.     

Skeletal muscle and peripheral nerve changes caused by chronic arterial insufficiency--significance and clinical correlations--histological, histochemical and ultrastructural study

A histological, histochemical and ultrastructural study on muscle changes in chronic arterial insufficiency has been carried out in 40 patients. Muscle biopsy probes were taken in each patient either from the gastrocnemius or rectus femoris. In 7 patients submitted for amputation of a lower limb due to a more severe vascular disease, specimens were also obtained from both the sciatic and sural nerve for light and electron microscopic study. Our findings confirm the previous histological, histochemical and ultrastructural data on chronic ischemia of the skeletal muscle, suggesting that muscle damage is mainly based on a neurogenic noxa initiated by an ischemic peripheral neuropathy. In addition, many morphologic features also show the presence of a primary myopathic noxa, possibly depending on the direct damage of the mitochondrial respiratory chain by the deficit of the muscle blood supply.     

Focal myopathy mimicking posterior interosseous nerve syndrome.

A 25-year-old man developed weakness of extension of the right index, middle, and fourth fingers at the metacarpophalangeal joints, over 2 years. No sensory deficit was present. Nerve conduction studies, including the right radial nerve, were within normal limits. Needle electromyographic (EMG) examination showed myopathic changes that were limited to the right extensor digitorum communis and extensor indicis proprius muscles. An intravenous edrophonium chloride test had no effect on weakness and repetitive stimulation showed no significant decremental response. An EMG-guided open biopsy of the extensor digitorum communis muscle revealed severe myopathic changes. Evaluation for the cause of myopathic involvement was negative. After 13 months, clinical examination and electrophysiological studies showed no significant progression. This case exemplifies the fact that a focal myopathy may mimic an entrapment neuropathy.     

Optimizing testing methods and collection of reference data for differentiating critical illness polyneuropathy from critical illness MYOPATHIES

Introduction: In severe acute quadriplegic myopathy in intensive care unit (ICU) patients, muscle fibers are electrically inexcitable; in critical illness polyneuropathy, the excitability remains normal. Conventional electrodiagnostic methods do not provide the means to adequately differentiate between them. In this study we aimed to further optimize the methodology for the study of critically ill ICU patients and to create a reference database in healthy controls. Methods: Different electrophysiologic protocols were tested to find sufficiently robust and reproducible techniques for clinical diagnostic applications. Results: Many parameters show large test–retest variability within the same healthy subject. Reference values have been collected and described as a basis for studies of weakness in critical illness. Conclusions: Using the ratio of neCMAP/dmCMAP (response from nerve and direct muscle stimulation), refractory period, and stimulus–response curves may optimize the electrodiagnostic differentiation of patients with critical illness myopathy from those with critical illness polyneuropathy. Muscle Nerve 53 : 555–563, 2016     

Quantitative neuromuscular ultrasound in intensive care unit–acquired weakness: A systematic review

Intensive care unit–acquired weakness (ICU‐AW) causes significant morbidity and impairment in critically ill patients. Recent advances in neuromuscular ultrasound (NMUS) allow evaluation of neuromuscular pathology early in critical illness. Here we review application of ultrasound in ICU‐AW. MEDLINE‐indexed articles were searched for terms relevant to ultrasound and critical illness. Two reviewers evaluated the resulting abstracts (n = 218) and completed full‐text review (n = 13). Twelve studies and 1 case report were included. Ten studies evaluated muscle thickness or cross‐sectional area (CSA): 8 reported a decrease, and 2 reported no change. Two studies reported preservation of muscle thickness in response to neuromuscular electrical stimulation, and 1 found no preservation. One study found decreases in gray‐scale standard deviation, but no change in echogenicity. One study described increases in echogenicity and fasciculations. Ultrasound reliability in ICU‐AW is not fully established. Further investigation is needed to identify ultrasound measures that reliably predict clinical, electrodiagnostic, and pathologic findings of ICU‐AW. Muscle Nerve 52 : 701–708, 2015     

Quantitative EMG of facial muscles in myasthenia patients with MuSK antibodies.

OBJECTIVE: Our aim was to study the pathophysiological process leading to facial muscle atrophy in 13 patients with MuSK antibody positive myasthenia gravis (MuSK-MG), and to compare with findings from 12 acetylcholine receptor antibody positive myasthenia patients (AChR-MG), selected because they suffered from the same degree of disease severity and required similar treatment. METHODS: Motor unit action potential (MUAP) and interference pattern analysis from orbicularis oculi (O oculi) and orbicularis oris (O oris) muscles were studied using a concentric needle electrode, and compared with findings in 20 normal subjects, 6 patients receiving botulinum toxin injections (representing a neurogenic model) and 6 patients with a muscle dystrophy (representing a myopathic model). The techniques and control data have been reported previously. RESULTS: The mean MUAP durations for O oculi and O oris were significantly reduced (p<0.001) in both MG cohorts when compared with healthy subjects, and were similar to those in the myopathic control group. They were significantly different from those obtained from the neurogenic control group (p<0.001 for both O oculi and O oris). The MUAP findings in O oculi occurred independently from neuromuscular blocking on single fibre EMG (SFEMG) in the same muscle. On turns amplitude analysis (TAA), 50% of MuSK-MG patients and 42% of AChR-MG patients had a pattern in O oculi which was similar to that in the myopathic control group, and 62% of MuSK-MG patients and 50% of AChR-MG patients had a pattern in O oris that was also similar to that in the myopathic control group. The TAA findings for O oculi and O oris in both MG cohorts were different from those obtained from the neurogenic control group. CONCLUSIONS: Facial muscle atrophy in MuSK-MG patients is not neurogenic and the pathophysiological changes are akin to a myopathic process. The selected AChR-MG patients also show evidence of a similar pathophysiological process in the facial muscles albeit to a lesser degree. SIGNIFICANCE: We propose that muscle atrophy in MuSK-MG is a myopathic process consisting of either muscle fibre shrinkage or loss of muscle fibres from motor units. The duration of disease and long-term steroid treatment may be further contributory factors.     

Axonal stimulation for end-plate jitter studies.

This single fibre EMG study compares the standard method of neuromuscular jitter measurement in voluntarily activated muscle to that by intramuscular electrical stimulation of motor axons in a group of normal subjects. The latter method avoids the interdischarge interval-dependent jitter, as well as a possible failure to recognise split muscle fibres. The mean MCD on axonal stimulation was only 5.2 microseconds less than in the voluntary activation study and was thus 8% more than theoretically expected for single motor end plates. The difference could be due to an axonal jitter and some other factors. Axonal stimulation has proved to be a relatively easy and reliable method for routine estimation of neuromuscular jitter, provided that the resolution of time measurement is better than 2 microseconds, so that low jitter due to occasional direct muscle fibre stimulation is not mistaken for a normal reading. The upper normal limits for the extensor digitorum communis muscle suggested by the present study are 40 microseconds (individual muscle fibres) and 25 microseconds (mean of 30 muscle fibres).     

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     

Responses of intercostal muscle biopsies from normal subjects and patients with myasthenia gravis

In order to evaluate the mechanisms of weakness in muscles of patients with myasthenia gravis (MG), intercostal muscle biopsies were obtained from 9 normal subjects and 6 MG patients, and the compound muscle action potential (AP) and tension responses to nerve and muscle stimulation, and contracture responses on exposure to caffeine, were monitored in vitro. In normal muscle, on stimulation of the nerve or muscle at 30 to 100 Hz, the AP responses showed decrement in amplitude, one-third of which was attributable to failure of neuromuscular transmission and two-thirds to failure of muscle membrane excitation. On stimulation at 1 to 5 Hz, the AP responses showed very little decrement, while the contractile responses showed significant fade in tension, due to failure of E-C coupling or contractility. In muscle from patients with generalized MG, stimulation of the nerve at all frequencies (1 to 100 Hz) caused much greater decrement in APs and fade in tension responses than in normal muscle, due mainly to failure of neuromuscular transmission. However, at 100 Hz, 40% of the decrement in APs was due to failure of muscle membrane excitation, and at 1 to 5 Hz, 40% of the fade in tension was due to failure of E-C coupling or contractility, as in normal muscle. On direct stimulation the contraction and half-relaxation times were slower and the tetanic tension was smaller than in normal muscle, especially in the MG patient with thymoma. Caffeine-induced contractures were smaller in MG muscle than in normal muscle. These results indicate that while the weakness of MG muscle is due mainly to failure of neuromuscular transmission, it is also partly due to reduced E-C coupling or contractility.     

胰岛素强化治疗应用于ICU获得性肌无力的临床疗效观察

目的观察胰岛素强化治疗ICU获得性肌无力患者的临床疗效。方法 52例获得性肌无力患者随机分为对照组和研究组各26例。对照组给予常规胰岛素治疗,血糖控制在180~200mg/dl,研究组给予强化胰岛素治疗,血糖控制在80~110mg/dl,其余治疗同对照组。记录并比较2组原发疾病后第1、2、3月英国医学研究委员会(MRC)肌力评分、改良Barthel指数评分(BMI)及2组机械通气时间、ICU住院时间及总住院时间。结果研究组不同测量时间点MRC、BMI评分均高于对照组(P均0.05),机械通气时间、ICU住院时间及总住院时间均少于对照组(P均0.05)。结论强化胰岛素治疗可控制ICUAW的发生及发展,改善患者预后。