Acute myopathy with selective degeneration of myosin filaments following status asthmaticus treated with methylprednisolone and vecuronium

Management of Polyneuromyopathy in a Critically Ill Patient with a Left Ventricular Assist Device

Critical illness polyneuromyopathy after cardiac surgery is often unrecognized and is a rarely reported clinical condition. It is characterized by more proximal than distal symmetrical flaccid muscle weakness and difficulty in weaning from a respirator. When done in a timely manner, rehabilitation prevents early complications and reduces the length of hospitalization. Rehabilitation leads to better motor outcome, improves short-term and long-term functionality, and results in a better quality of life.

Approach to critical illness myopathy and polyneuropathy in the older SARS-CoV-2 patients

One of the major concerns of the health care community and the public surrounding the SARS-CoV-2 pandemic is the availability and use of ventilators. Unprecedented surges of patients presented to intensive care units across the country, with older adults making up a large proportion of the patient population. This paper illustrates contemporary approaches to critical illness myopathy (CIM), critical illness polyneuropathy (CIP), and critical illness polyneuromyopathy (CIPNM) in older patients, including incidence, risk factors, mechanisms for pathology, diagnosis, contemporary treatment approaches, and outcomes. We hope that the following analysis may help educate clinicians and ultimately decrease the duration of the mechanical ventilation required by these patients, resulting in improved clinical outcomes and an increase in ventilator availability for other patients in need.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

Review of Critical Illness Myopathy and Neuropathy

Critical illness myopathy (CIM) and neuropathy are underdiagnosed conditions within the intensive care setting and contribute to prolonged mechanical ventilation and ventilator wean failure and ultimately lead to significant morbidity and mortality. These conditions are often further subdivided into CIM, critical illness polyneuropathy (CIP), or the combination-critical illness polyneuromyopathy (CIPNM). In this review, we discuss the epidemiology and pathophysiology of CIM, CIP, and CIPNM, along with diagnostic considerations such as detailed clinical examination, electrophysiological studies, and histopathological review of muscle biopsy specimens. We also review current available treatments and prognosis. Increased awareness and early recognition of CIM, CIP, and CIPNM in the intensive care unit setting may lead to earlier treatments and rehabilitation, improving patient outcomes.

Pathophysiology of muscle dysfunction in COPD

Muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD) and may involve both respiratory and locomotor (peripheral) muscles. The loss of strength and/or endurance in the former can lead to ventilatory insufficiency, whereas in the latter it limits exercise capacity and activities of daily life. Muscle dysfunction is the consequence of complex interactions between local and systemic factors, frequently coexisting in COPD patients. Pulmonary hyperinflation along with the increase in work of breathing that occur in COPD appear as the main contributing factors to respiratory muscle dysfunction. By contrast, deconditioning seems to play a key role in peripheral muscle dysfunction. However, additional systemic factors, including tobacco smoking, systemic inflammation, exercise, exacerbations, nutritional and gas exchange abnormalities, anabolic insufficiency, comorbidities and drugs, can also influence the function of both respiratory and peripheral muscles, by inducing modifications in their local microenvironment. Under all these circumstances, protein metabolism imbalance, oxidative stress, inflammatory events, as well as muscle injury may occur, determining the final structure and modulating the function of different muscle groups. Respiratory muscles show signs of injury as well as an increase in several elements involved in aerobic metabolism (proportion of type I fibers, capillary density, and aerobic enzyme activity) whereas limb muscles exhibit a loss of the same elements, injury, and a reduction in fiber size. In the present review we examine the current state of the art of the pathophysiology of muscle dysfunction in COPD.

Electrophysiology of neuromuscular disorders in critical illness

INTRODUCTION

Neuromuscular disorders, predominantly critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) occur in approximately one-third of patients in intensive care units. The aim of this study was to review the important role of electrophysiology in this setting.

RESULTS

In CIM, sarcolemmal inexcitability causes low amplitude compound muscle action potentials (CMAPs) that may have prolonged durations. Needle electrode examination usually reveals early recruitment of short duration motor unit potentials, often with fibrillation potentials. In CIP, the findings are usually those of a generalized axonal sensorimotor polyneuropathy. Direct muscle stimulation aids in differentiating CIP and CIM and in identifying mixed disorders along with other electrodiagnostic and histopathologic studies. Identifying evolving reductions in fibular CMAP amplitudes in intensive care unit (ICU) patients predicts development of neuromuscular weakness.

CONCLUSIONS

Knowledge of the various neuromuscular disorders in critically ill patients, their risk factors, and associated electrodiagnostic findings can lead to development of a rational approach to diagnosis of the cause of neuromuscular weakness in ICU patients.

Respiratory diseases and muscle dysfunction

Many respiratory diseases lead to impaired function of skeletal muscles, influencing quality of life and patient survival. Dysfunction of both respiratory and limb muscles in chronic obstructive pulmonary disease has been studied in depth, and seems to be caused by the complex interaction of general (inflammation, impaired gas exchange, malnutrition, comorbidity, drugs) and local factors (changes in respiratory mechanics and muscle activity, and molecular events). Some of these factors are also present in cystic fibrosis and asthma. In obstructive sleep apnea syndrome, repeated exposure to hypoxia and the absence of reparative rest are believed to be the main causes of muscle dysfunction. Deconditioning appears to be crucial for the functional impairment observed in scoliosis. Finally, cachexia seems to be the main mechanism of muscle dysfunction in advanced lung cancer. A multidimensional therapeutic approach is recommended, including pulmonary rehabilitation, an adequate level of physical activity, ventilatory support and nutritional interventions.

Neuromuscular disorders in critically ill patients: review and update

Neuromuscular disorders that are diagnosed in the intensive care unit (ICU) usually cause substantial limb weakness and contribute to ventilatory dysfunction. Although some lead to ICU admission, ICU-acquired disorders, mainly critical illness myopathy (CIM) and critical illness polyneuropathy (CIP), are more frequent and are associated with considerable morbidity. Approximately 25% to 45% of patients admitted to the ICU develop CIM, CIP, or both. Their clinical features often overlap; therefore, nerve conduction studies and electromyography are particularly helpful diagnostically, and more sophisticated electrodiagnostic studies and histopathologic evaluation are required in some circumstances. A number of prospective studies have identified risk factors for CIP and CIM, but their limitations often include the inability to separate CIM from CIP. Animal models reveal evidence of a channelopathy in both CIM and CIP, and human studies also identified axonal degeneration in CIP and myosin loss in CIM. Outcomes are variable. They tend to be better with CIM, and some patients have longstanding disabilities. Future studies of well-characterized patients with CIP and CIM should refine our understanding of risk factors, outcomes, and pathogenic mechanisms, leading to better interventions.

Severe weakness complicating status asthmaticus despite minimal duration of neuromuscular paralysis

OBJECTIVE

Mechanically ventilated patients with status asthmaticus who undergo prolonged paralysis are at risk for severe weakness due to myopathy. In the mid-1990s, we changed our usual method of achieving tolerance of ventilatory support in asthmatic patients from continuous paralysis to deep sedation. This study examines the impact of this change in practice on the development of clinically significant weakness in status asthmaticus.

DESIGN AND SETTING

Retrospective cohort study in university-affiliated county hospital.

PATIENTS

Mechanically ventilated asthmatic patients seen before (n = 96) and after (n = 74) a clinical practice change in 1995 that markedly restricted use of paralytics.

RESULTS

The duration of neuromuscular paralysis declined sharply after 1995 (23.7 +/- 42.2 vs. 1.8 +/- 4.0 h, P < 0.001), but this was not associated with a significant difference in the incidence of weakness (21 vs. 14%, P = 0.23). Within the post-1995 cohort, there was no significant difference in the duration of paralysis for weak and non-weak patients (3.5 +/- 6.2 vs. 1.5 +/- 3.5 h, P = 0.10). However, weak patients had a much longer duration of mechanical ventilation than did patients without weakness (11.9 +/- 3.6 vs. 1.9 +/- 1.8 days, P < 0.001).

CONCLUSION

Mechanically ventilated patients with status asthmaticus who are immobilized for prolonged periods of time by deep sedation remain at risk for clinically significant weakness.

Myopathy in horses with pituitary pars intermedia dysfunction (Cushing’s disease)

Fifteen horses with pituitary pars intermedia dysfunction were studied. The horses were of various breeds and between 15 and 28 years of age. Control horses matched for breed and age were studied for comparison. Evaluations included complete blood cell count and serum biochemical analysis, electromyography, and gluteus medius muscle biopsies for histochemical, morphometric, and ultrastructural analysis. No differences were found between groups of horses on routine laboratory analysis or electromyography. We demonstrated that muscle wasting in diseased horses was the result of atrophy of types 2A and 2B muscle fibers and loss of type 2B myofibers. Mild non-specific non-inflammatory myopathic alterations such as myofiber size variation, internal nuclei, perimysial, endomysial and sarcoplasmic fat accumulation were observed. At the ultrastructural level, subsarcolemmal mitochondrial accumulation and increased lipid droplets were evident. Similar to other species, this study confirmed atrophy of type 2 fibers as the cause of muscle mass loss in horses with Cushing's disease.

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.

Neuromuscular disorders in the intensive care unit

Neuromuscular disorders encountered in the ICU can be categorized as muscular diseases that lead to ICU admission and those that are acquired in the ICU. This article discusses three neuromuscular disorders can lead to ICU admission and have a putative immune-mediated pathogenesis: the Guillian-Barré syndrome, myasthenia gravis, and dermatomyositis/polymyositis. It also reviews critical care polyneuropathy and ICU acquired myopathy, two disorders that, alone or in combination, are responsible for nearly all cases of severe ICU acquired muscle weakness.

Acute quadriplegia and loss of muscle myosin in patients treated with nondepolarizing neuromuscular blocking agents and corticosteroids: mechanisms at the cellular and molecular levels

OBJECTIVE

Long-term treatment with nondepolarizing neuromuscular blocking agents and corticosteroids in the intensive care unit is not benign, and an increasing number of patients with acute quadriplegic myopathy have been reported with increased use of these drugs. The purpose of this study was to investigate the mechanisms underlying acute quadriplegic myopathy.

DESIGN

Percutaneous muscle biopsy samples were obtained, and electrophysiologic examinations were performed during the acute phase and during recovery in patients with acute quadriplegic myopathy. Regulation of muscle contraction and myofibrillar protein synthesis was studied using cell physiologic techniques, ultrasensitive electrophoresis, in situ hybridization, and histopathologic techniques.

SETTING

All patients were seen in the intensive care unit of different university hospitals.

PATIENTS

All patients were critically ill with sepsis. They had been given massive doses of corticosteroids in combination with variable doses of neuromuscular blocking agents. All patients developed paralysis of spinal nerve-innervated muscles. On the other hand, cranial nerve-innervated muscle and sensory and cognitive functions were well maintained after discontinuation of treatment with neuromuscular blocking agents.

INTERVENTION

Muscle biopsy samples were obtained and electrophysiologic examinations were performed in all patients.

MEASUREMENTS AND MAIN RESULTS

The major observations in patients with acute quadriplegic myopathy were, as follows: a) a general decrease in myofibrillar protein content; b) specific but highly variable partial or complete loss of myosin and myosin-associated proteins; c) very low thick-filament/thin-filament protein ratios; d) absence of myosin messenger RNA; and e) a dramatically impaired muscle cell force-generating capacity in the acute phase of acute quadriplegic myopathy. During clinical improvement, normal expression of myosin messenger RNAs, reexpression of thick-filament proteins, and increased specific tension were observed.

CONCLUSIONS

Acute quadriplegic myopathy is associated with a specific decrease in thick-filament proteins related to an altered transcription rate. Although the decreased content of thick-filament proteins is important for prolonged muscle weakness, it is not the primary cause of muscle paralysis in the acute stage, during which impaired muscle membrane excitability probably plays a more significant role. Several factors contribute to this condition, but the action of corticosteroids seems to be the predominant one, along with potentiation by neuromuscular blocking agents, immobilization, and probably also concurrent sepsis.

Myopathy in critically ill patients

OBJECTIVE

To review myopathic changes occurring during intensive care treatment in the light of recent information about manifestation, clinical settings, pathophysiology, and histomorphologic changes.

DATA SOURCES

The computerized MEDLINE database, bibliography of pertinent articles, and the author's personal files.

STUDY SELECTION

Studies were selected according to their relevance to myopathic complications in critically ill patients.

DATA EXTRACTION

All applicable data were extracted.

DATA SYNTHESIS

Myopathic changes occur frequently in patients treated in the intensive care unit (ICU). Three main types have been identified: critical illness myopathy, myopathy with selective loss of myosin filaments, and acute necrotizing myopathy of intensive care. These histologic types probably represent variable expressions of a toxic effect not yet identified. Candidates for such myotoxic effects are the mediators of the systemic response in sepsis and high-dose administration of corticosteroids and muscle relaxants. The influence of these latter agents appears to be particularly important in the pathogenesis of myosin loss and myonecrosis. Experimental studies suggest that axonal damage attributable to critical illness neuropathy can be an additional factor triggering myopathies in the ICU. Muscle membrane inexcitability was recently identified as an alternative mechanism of severe weakness in ICU patients.

CONCLUSIONS

Myopathic changes are surprisingly frequent in critically ill patients. The clinical importance of this finding is still unknown, but it is likely that weakness caused by myopathy prolongs ICU stay and rehabilitation. Because corticosteroids and muscle relaxants appear to trigger some types of ICU myopathy, they should be avoided or administered at the lowest doses possible. Sepsis, denervation, and muscle membrane inexcitability may be additional factors. Studies addressing the pathophysiology of myopathy in critically ill patients are urgently needed.

Muscle fibre atrophy in critically ill patients is associated with the loss of myosin filaments and the presence of lysosomal enzymes and ubiquitin

Muscle wasting and weakness are common features of patients with critical illnesses, and may impair their recovery. This study examines whether cytoskeletal and contractile proteins are damaged, and which proteolytic mechanisms might be involved, in the muscle fibre atrophy or necrosis associated with the acute myopathy of critically ill patients. Ninety-eight muscle biopsies were obtained by the conchotome method from 57 critically ill patients and examined morphometrically and by immunohistochemical labelling. Sequential biopsies showed a mean reduction in fibre cross-sectional areas of 3-4% per day. More intense immunolabelling for desmin was seen in the smaller fibres of 52% of the biopsies, while immunolabelling for dystrophin, actin and myosin heavy chains was maintained. Myosin ATPase activity was weak in the smaller fibres in some biopsies, and electron microscopy showed the loss of myosin filaments in atrophic fibres. These changes suggest that loss of the filamentous structure of myosin, without degradation of the immunolabelled epitopes, leads to the collapse of the intermyofibrillar desmin network. Fibres with abnormal desmin labelling showed increased cathepsin B, lysozyme and ubiquitin immunolabelling. Nine cases showed increased immunolabelling for heat shock protein 72. The changes in desmin immunolabelling were more prevalent in patients with higher APACHE II scores on admission, but were not related to other clinical features. The results indicate that fibre atrophy is associated with myosin filament depolymerization and the presence of several proteolytic enzymes. In our study, these changes occurred in patients who were critically ill but who did not receive large doses of steroids or neuromuscular blocking agents.

N lines in a myopathy with myosin loss

N lines can be seen by electron microscopy within the I band of skeletal muscle, but are poorly visualized in conventional preparations. We present a case of acute quadriplegic myopathy with myosin loss and prominent N lines. The only other reported cases of N lines were also seen in patients with myosin loss from diverse etiologies. Myosin loss and the subsequent detachment of titin from myosin may result in the formation of prominent N lines.

Causes of neuromuscular weakness in the intensive care unit: a study of ninety-two patients

The spectrum of neuromuscular disorders among intensive care unit (ICU) patients has shifted toward disorders acquired within the ICU and away from "traditional" neuromuscular disorders that lead to ICU admission. We sought to assess this spectrum by determining the causes and relative frequencies of neuromuscular disorders that led to electromyography (EMG) examinations in our ICU population. Ninety-two patients were studied over a 4 1/2-year period. Twenty-six (28%) had neuromuscular disorders (mainly Guillain-Barré syndrome, myopathy, and motor neuron disease) that led to ICU admission. Among patients who developed weakness in the ICU, there was a predominance of organ transplant patients and patients with the systemic inflammatory response syndrome and multiorgan dysfunction. Thirty-nine (42%) developed acute myopathy (consistent with critical illness myopathy in most), and 13% developed acute axonal sensorimotor polyneuropathy (mainly critical illness polyneuropathy). Patients with acute myopathy and acute axonal sensorimotor polyneuropathy had similar functional outcomes. We conclude that among patients who underwent EMG in our ICU population, acute myopathy is three times as common as acute axonal polyneuropathy, and the outcomes from acute myopathy and acute axonal polyneuropathy may be similar.

Loss of electrical excitability in an animal model of acute quadriplegic myopathy

In rats treated with high-dose corticosteroids, skeletal muscle that is denervated in vivo (steroid-denervated [S-D]) develops electrical inexcitability similar to that seen in patients with acute quadriplegic myopathy. In studies of affected muscles in vitro, the majority of S-D fibers failed to generate action potentials in response to intracellular stimulation although the average resting potential of these fibers was no different from that of control denervated muscle. The downregulation of membrane chloride conductance (G[Cl]) seen in normal muscle after denervation did not occur in S-D muscle. Although block of chloride channels in S-D muscle produced high specific membrane resistance, comparable to similarly treated control denervated muscle, and partially restored excitability in many fibers, action potential amplitude was still reduced in S-D fibers, suggesting a concomitant reduction in sodium current. 3H-saxitoxin binding measurements revealed a reduction in the density of the adult muscle sodium channel isoform in S-D muscle, suggesting that a decrease in the number of sodium channels present may play a role in the reduction of sodium current, although altered properties of channels may also contribute. The weakness seen in S-D muscle may involve the interaction of a number of factors that modify membrane excitability, including membrane depolarization, persistence of G(Cl), and reduced voltage-gated sodium currents.

Acute corticosteroid myopathy in intensive care patients

Several recent studies have attributed the occurrence of acute myopathy in intensive care unit patients to the combination of corticosteroids and neuromuscular junction blocking agents (NMBAs) used for mechanical ventilation. We present 4 patients who developed acute myopathy after administration of high doses of glucocorticoids during sedation with propofol without any NMBAs. All patients had elevated creatine kinase levels. Electrophysiological studies indicated normal motor and sensory nerve conduction velocities but reduced motor nerve response amplitudes. Needle electromyography identified abnormal spontaneous activity; motor unit potentials were polyphasic of low amplitude and short duration, characteristic of a myopathic process. Muscle biopsy demonstrated a prominent acute necrotizing myopathy in all 4 patients with a loss of thick filaments. Our observations support glucocorticoids rather than NMBAs as the main offending drug in acute corticosteroid myopathy. The predisposing factor should be the hypersensitivity of paralyzed muscles to corticosteroids regardless of the drug inducing paralysis: NMBAs or propofol.

Evaluation and treatment of respiratory failure in neuromuscular disease

Respiratory failure is a relatively uncommon feature of most neuromuscular disease. It accounts for most of the morbidity and mortality associated with these disorders, however. In most cases, aggressive supportive care, specific immunologic treatment, and treatment of associated medical conditions result in improvement in respiratory function and a favorable outcome.

Acute myopathy of intensive care: clinical, electromyographic, and pathological aspects

An acute myopathy of intensive care occurs in critically ill patients treated with intravenous corticosteroids and neuromuscular junction-blocking agents. The full clinicopathological spectrum is uncertain. We evaluated the clinical, electrodiagnostic, and histopathological features of 14 patients who developed acute myopathy of intensive care after organ transplantation or during treatment of severe pulmonary disorders and sepsis. Patients received high-dose intravenous corticosteroids, usually in conjunction with relatively low to moderate doses of neuromuscular junction-blocking agents. After discontinuation of the latter drugs, most had diffuse, flaccid weakness with failure to wean from mechanical ventilation. Electrodiagnostic findings were consistent with a necrotizing myopathy. Muscle histopathology revealed myopathy with loss of thick filaments in 79%, mild myopathic changes in 14%, and atrophy of type 1 and type 2 fibers in 7%. Loss of thick filaments was identified in muscle biopsy specimens obtained 30 +/- 11 days (mean +/- standard deviation) after intravenous corticosteroid treatment but not in those obtained earlier (12 +/- 2 days). Critically ill patients, including those receiving organ transplants, may develop acute myopathy of intensive care after exposure to intravenous corticosteroids and neuromuscular junction-blocking agents, although the exposure to the latter drugs may be minimal. Selective loss of thick filaments is common in acute myopathy of intensive care, especially if the muscle biopsy specimen is obtained 2 weeks or more after intravenous corticosteroid exposure.

Economic impact of prolonged motor weakness complicating neuromuscular blockade in the intensive care unit

OBJECTIVE

We compared a case-series of ten patients who developed prolonged neuromuscular weakness after continuous, nondepolarizing, neuromuscular blockade with a group of controls without neuromuscular weakness to determine the economic impact of the neuromuscular weakness.

DESIGN

Frequency-matched case control trial.

SETTING

Medical and surgical intensive care units of a 937-bed tertiary care, university-affiliated teaching hospital.

PATIENTS

Ten patients developed prolonged neuromuscular weakness after continuous administration of nondepolarizing neuromuscular blockers. Ten patients from a 1994 drug utilization database who did not develop motor weakness after paralysis were identified to serve as controls.

MEASUREMENTS AND MAIN RESULTS

The medical and accounting records of the patients were retrospectively reviewed. Charge data were obtained from patient accounts. Institutional ratios to convert charges to full costs and marginal costs were obtained from the Hospital Finance Department of Henry Ford Hospital. The economic impact of the diagnosis and recovery of the motor weakness was estimated for the intensive care unit (ICU) and hospital stays and compared with those values for control patients. Median hospital charges (excluding rehabilitation), totaling $91,476, were attributed to the patients who developed neuromuscular weakness and included charges for neuromuscular blocking agents, continuous mechanical ventilation, ICU and hospital beds, neurologic studies, and physical therapy services. In the control patients, median charges were $22,191 (p = .001). The total median cost differential for a patient in the neuromuscular weakness group was in excess of $66,713 (95% confidence interval $23,485 to $189,214, p = .001). Significant differences were also found for patient charges, full costs, and marginal costs for mechanical ventilation (p = .002), neurologic studies (p = .014), as well as ICU (p = .002) and hospital (p = .001) stays.

CONCLUSIONS

The development of motor weakness was associated with an increase in ICU and hospital stays, continued mechanical ventilation, and disproportionate healthcare expenditures in excess of $66,000 per patient. A prospective evaluation of the true prevalence of neuromuscular weakness after neuromuscular blockade and of the costs to the healthcare system is needed.

Generalized Paralysis in the Intensive Care Unit: Emphasis on the Complications of Neuromuscular Blocking Agents and Corticosteroids

Generalized weakness in intensive care unit (ICU) patients is increasingly recognized as a frequent complication and a common cause of prolonged ventilator dependency. Intravenous corticosteroids and neuromuscular blocking agents, sepsis, and multiorgan failure have been strongly implicated in the ICU paralysis syndromes, but the pathophysiology of these disorders is poorly understood. The combination of neuromuscular blocking agents and corticosteroids may induce three distinct syndromes of generalized weakness in ICU patients: acute myopathy, prolonged neuromuscular blockade, and critical illness polyneuropathy. 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, electrodi-agnostic, and histological evaluation. Acute myopathy with generalized weakness, preserved eye movements, elevated creatine kinase levels, and myopathic motor units on electromyography (EMG) have developed in asthmatics requiring neuromuscular blockers and steroids. Muscle biopsy has shown distinctive changes, with fiber atrophy, scattered necrosis, and thick (myosin) filament depletion on ultrastructural studies. Patients who have had a prolonged ICU stay or sepsis with failure to wean from the ventilator, distal weakness, and areflexia probably have critical illness polyneuropathy. EMG in these patients has demonstrated reduced or absent motor and sensory potentials with neurogenic motor units. Prolonged neuromuscular blockade most commonly has occurred in patients with renal failure who received prolonged infusions of neuromuscular blockers. Severe flaccid, areflexic paralysis with normal sensation, facial weakness, and ophthalmoparesis persists for days or weeks after the neuromuscular blockers have been discontinued. Repetitive nerve stimulation has shown a decrement of the compound muscle action potential, and it establishes a disorder of neuromuscular transmission in most patients. We critically examine the clinical, electrophysiological, and pathological features of each of these syndromes, and we summarize current understanding of the pathophysiology of these disorders and the relationship to neuromuscular blocking agents and corticosteroids.

Congenital myopathies

The congenital myopathies (CM) are a group of non or little progressive neuromuscular conditions, often hereditary, delineated by morphological techniques, ie, enzyme histochemistry and electron microscopy. The catalogue of CM entailing well known "classic" conditions as central core disease, nemaline myopathy, and centronuclear myopathy has continuously been expanded, now comprising some 40 conditions. Nosologic advances have occurred with immunohistochemical techniques that show generalized or focal protein abnormalities within muscle fibers of certain CM, but at much slower pace as to localization of CM genes. So far, only those for central core disease, nemaline myopathy, and myotubular myopathy have been reported. Epidemiological rarity and nosographic controversy of CM have contributed to this lack of molecular genetic progress in CM.

Neuromuscular complications in the ICU: the spectrum of critical illness-related conditions causing muscular weakness and weaning failure

Muscular weakness and atrophy in intensive care patients has long been attributed to a combination of immobilization and cataboly. More recently, it has become apparent that specific injuries to the peripheral nerve, the neuromuscular junction and the muscle are more likely causes of weakness in these patients. Clinically, delayed weaning from the ventilator and prolonged neurologic rehabilitation are the most important consequences. Detailed electrodiagnostic examination is necessary for accurate diagnosis. In selected patients, a combined muscle and nerve biopsy is helpful. In this review, I describe the current knowledge of neuromuscular complications in patients with long-term treatment in the intensive care unit.

Technical and interpretive problems of peripheral nerve stimulation in monitoring neuromuscular blockade in the intensive care unit

OBJECTIVE

To review the literature and provide an overview of the technical and interpretive problems associated with peripheral nerve stimulation in monitoring neuromuscular blockade in the intensive care unit.

DATA SOURCES

A computerized search on MEDLINE from 1985 through 1994 was performed to identify English-language comparative studies, abstracts, and review articles pertaining to peripheral nerve stimulation, train-of-four monitoring, and neuromuscular blockade in the critical care setting.

STUDY SELECTION AND DATA EXTRACTION

Relevant studies in humans were selected and information was extracted on the use of peripheral nerve monitoring in the critically ill.

DATA SYNTHESIS

Use of peripheral nerve stimulation is complicated in the intensive care unit. Problems may occur with the patient, the device, as well as operator technique, all of which may lead to errors in interpretation of the depth of paralysis. The critically ill patient has changing comorbid disease states and total body water composition, which may impair the accuracy or reproducibility of measurements. Technical problems relate to the operation of the device, electrode placement, and suboptimal delivery of the desired current. Difficulties in performing peripheral nerve stimulation and interassessor variability contribute to errors of interpretation.

CONCLUSIONS

These difficulties compromise the precision, accuracy, and reliability of the peripheral nerve stimulator as a tool for monitoring neuromuscular blockade in the critically ill. Peripheral nerve stimulation should be used in conjunction with clinical parameters to make decisions regarding dose adjustments. Doses should be reduced as much as possible to provide the minimum depth of paralysis that is clinically appropriate. Technical directions and training programs for peripheral nerve stimulation should be developed, and designated individuals should be trained in its application. Large, prospective, controlled studies are necessary to evaluate the incidence of prolonged paralysis or motor neuropathy with administration of neuromuscular blocking agents in patients whose dose is adjusted on the basis of peripheral nerve stimulation.

Neuromuscular complications of sepsis in children

Sepsis occurs frequently in the pediatric intensive care unit and is a significant cause of morbidity and mortality. Multiple organ systems are adversely affected by sepsis. Approximately 70% of adult patients with sepsis have peripheral nervous system dysfunction on electrophysiologic studies, of whom 30% are symptomatic. Neuromuscular dysfunction in children with sepsis is increasingly reported; however, the incidence remains undefined. Flaccid quadriplegia with the inability to wean from ventilatory support despite full cardiopulmonary recovery is the typical presentation. However, lesser degrees of weakness may be demonstrated with careful evaluation. Electrophysiologic studies often demonstrate the presence of axonal polyneuropathies, abnormalities of neuromuscular transmission, or acute myopathies. Identifiable neuromuscular syndromes in children with sepsis include critical illness polyneuropathy, pure motor polyneuropathy, thick-filament myopathy, and necrotizing myopathy. The common underlying pathogenic process in these syndromes appears to be sepsis, which may be accentuated by the administration of steroids or neuromuscular blocking agents. Recovery in strength usually occurs over a period of weeks to months.

Prolonged paralysis due to nondepolarizing neuromuscular blocking agents and corticosteroids

The long-term use of nondepolarizing neuromuscular blocking agents (ND-NMBA) has recently been implicated as a cause of prolonged muscle weakness, although the site of the lesion and the predisposing factors have been unclear. We report 3 patients (age 37-52 years) with acute respiratory insufficiency who developed prolonged weakness following the discontinuation of ND-NMBAs. Two patients also received intravenous corticosteroids. Renal function was normal but hepatic function was impaired in all patients, and all had acidosis. Electrophysiologic studies revealed low amplitude compound motor action potentials, normal sensory studies, and fibrillations. Repetitive stimulation at 2 Hz showed a decremental response in 2 patients. The serum vecuronium level measured in 1 patient 14 days after the drug had been discontinued was 172 ng/mL. A muscle biopsy in this patient showed loss of thick, myosin filaments. The weakness in these patients is due to pathology at both the neuromuscular junction (most likely due to ND-NMBA) and muscle (most likely due to corticosteroids). Hepatic dysfunction and acidosis are contributing risk factors.

Acute necrotizing myopathy of intensive care: electrophysiological studies

A series of recent reports have identified cases of a quadriplegic myopathy characterized by myofiber necrosis and loss of myosin filaments associated with the use of nondepolarizing muscle blocking agents and glucocorticoids. We report electrophysiological findings in 7 intensive care unit patients who developed evidence of an acute myopathy in association with the use of nondepolarizing muscle blocking agents. Several important features were identified: (i) a neuromuscular transmission deficit was observed in 3 patients up to 7 days following withdrawal of vecuronium; (ii) motor M potentials were of low amplitude, there was mild abnormal spontaneous activity on needle electromyography, and sensory conduction was relatively preserved; (iii) not all patients received glucocorticoids or were asthmatic; (iv) 2 patients given vecuronium had very high creatine kinase levels and developed acute renal failure associated with myoglobinuria; and (v) rises in motor M potentials accompanied clinical recovery. This complication of intensive care may be severe, but is reversible and possibly avoidable. Our findings implicate nondepolarizing muscle blocking agents in the development of the myopathy. Electrophysiological studies provide important prognostic guidance.

Rapidly evolving myopathy with myosin-deficient muscle fibers

Five patients with rapidly evolving, severe weakness had an unusual myopathy with virtually complete loss of myosin in 5 to 40% of muscle fibers. Three of the 5 patients began to develop weakness 1 to 2 weeks after lung transplantation. The fourth became weak after a febrile illness. The fifth presented with diabetic ketoacidosis and weakness. All patients had received corticosteroid therapy. In all cases the weakness was progressive and led to severe disability, with respiratory failure in 4 patients. Initial diagnostic testing did not localize an underlying cause for the weakness. Creatine kinase was normal or minimally elevated. Electromyography generally showed mildly myopathic or nondiagnostic changes. However, muscle biopsy revealed numerous small angular fibers with no myosin ATPase staining at any pH. Immunocytochemical staining and ultrastructural studies confirmed a severe loss of myosin in many fibers. This rapidly evolving myopathy with myosin-deficient muscle fibers appears to be different clinically and pathologically from previously described syndromes involving rapidly progressive weakness. Slow recovery over a period of months is the most common outcome.

Mitochondrial changes in acute myopathy after treatment of respiratory failure with mechanical ventilation (acute relaxant-steroid myopathy)

A case of acute myopathy was observed in the course of treatment of respiratory failure with mechanical ventilation combined with prolonged neuromuscular blockade and administration of corticosteroids. A muscle biopsy revealed degeneration of muscle fibres. Electron microscopy showed loss of thick filaments as well as nemaline rods, vacuoles and cytoplasmic bodies. The mitochondria were increased in number, many harbouring paracrystalline inclusions, which were hitherto unknown in this condition.