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.     

MScanFit motor unit number estimation and muscle velocity recovery cycle recordings in diabetic polyneuropathy

ObjectiveMotor Unit Number Estimation (MUNE) methods may be valuable in tracking motor unit loss in diabetic polyneuropathy (DPN). Muscle Velocity Recovery Cycles (MVRCs) provide information about muscle membrane properties. This study aimed to examine the utility of the MScanFit MUNE in detecting motor unit loss and to test whether the MVRCs could improve understanding of DPN pathophysiology.MethodsSeventy-nine type-2 diabetic patients were compared to 32 control subjects. All participants were examined with MScanFit MUNE and MVRCs in anterior tibial muscle. Lower limb nerve conduction studies (NCS) in peroneal, tibial and sural nerves were applied to diagnose large fiber neuropathy.ResultsNCS confirmed DPN for 47 patients (DPN + ), with 32 not showing DPN (DPN−). MScanFit showed significantly decreased MUNE values and increased motor unit sizes, when comparing DPN + patients with controls (MUNE = 71.3 ± 4.7 vs 122.7 ± 3.8), and also when comparing DPN− patients (MUNE = 103.2 ± 5.1) with controls. MVRCs did not differ between groups.ConclusionsMScanFit is more sensitive in showing motor unit loss than NCS in type-2 diabetic patients, whereas MVRCs do not provide additional information.SignificanceThe MScanFit results suggest that motor changes are seen as early as sensory, and the role of axonal membrane properties in DPN pathophysiology should be revisited.     

重症监护病房获得性肌无力的发病机制研究现状及展望

重症监护病房获得性肌无力（intensive care unit acquired weakness,ICUAW）是重症监护病房患者出现的进行性全身肢体无力,且除危重病本身外无其他原因可解释的一组临床综合征,主要表现为神经肌肉功能障碍。ICUAW的发病机制涉及中枢、周围神经系统和肌纤维内复杂的功能、结构改变,但尚未完全明确。该文综述了目前关于ICUAW的潜在发病机制,以期对ICUAW的诊治提供新思路。 [国际神经病学神经外科学杂志, 2023, 50(2): 62-66]     

Neurological complications of sepsis: critical illness polyneuropathy and myopathy

Sepsis may cause not only failure of parenchymal organs but can also cause damage to peripheral nerves and skeletal muscles. It is now recognized that sepsis-mediated disorders of the peripheral nerves and the muscle, called critical illness polyneuropathy (CIP) and critical illness myopathy, are responsible for weakness and muscle atrophy occurring de novo in intensively treated patients. CIP represents an acute axonal neuropathy that develops during treatment of severely ill patients and remits spontaneously, once the critical condition is under control. The course is monophasic and self-limiting. Among the critical illness myopathies, three main types have been identified: a non-necrotizing “cachectic” myopathy (critical illness myopathy in the strict sense), a myopathy with selective loss of myosin filaments (“thick filament myopathy”) and an acute necrotizing myopathy of intensive care. Clinical manifestations of both critical illness myopathies and CIP include delayed weaning from the respirator, muscle weakness, and prolonging of the mobilization phase. The pathogenesis of these neuromuscular complications of sepsis is not understood in detail but most authors assume that the inflammatory factors that mediate systemic inflammatory response and multiple organ failure are closely involved. In thick filament myopathy and acute necrotizing myopathy, administration of steroids and neuromuscular blocking agents may act as triggers. Specific therapies have not been discovered. Stabilization of the underlying critical condition and elimination of sepsis appear to be of major importance. Steroids and muscle relaxants should be avoided or administered at the lowest dose possible. Received: 12 April 2001, Accepted: 23 April 2001     

Assessment of intensive care unit‐acquired weakness in young and old mice: An E. coli septic peritonitis model

Introduction: There are few reports of in vivo muscle strength measurements in animal models of ICU‐acquired weakness (ICU‐AW). In this study we investigated whether the Escherichia coli (E. coli) septic peritonitis mouse model may serve as an ICU‐AW model using in vivo strength measurements and myosin/actin assays, and whether development of ICU‐AW is age‐dependent in this model. Methods: Young and old mice were injected intraperitoneally with E. coli and treated with ceftriaxone. Forelimb grip strength was measured at multiple time points, and the myosin/actin ratio in muscle was determined. Results: E. coli administration was not associated with grip strength decrease, neither in young nor in old mice. In old mice, the myosin/actin ratio was lower in E. coli mice at t = 48 h and higher at t = 72 h compared with controls. Conclusions: This E. coli septic peritonitis mouse model did not induce decreased grip strength. In its current form, it seems unsuitable as a model for ICU‐AW. Muscle Nerve 53 : 127–133, 2016     

Detecting peripheral motor nervous system involvement in chronic spinal cord injury using two novel methods: MScanFit MUNE and muscle velocity recovery cycles

ObjectiveTo examine the peripheral nervous system (PNS) in spinal cord injured (SCI) patients using two novel methods: (1) MScanFit MUNE; a motor unit number estimation method detecting motor unit loss and (2) muscle velocity recovery cycles (MVRCs) measuring muscle membrane properties which has previously shown depolarization of the muscle membrane in denervated muscles.MethodsThirty chronic SCI patients (lesion above Th10) and twenty-five gender –and age matched healthy controls (HC) were examined. MScanFit was recorded from peroneal nerve to anterior tibial muscle (TA) and tibial nerve to abductor hallucis muscle after excluding localized mononeuropathies. MVRCs were recorded from TA.ResultsNerve conduction studies showed mononeuropathy in 8 patients (27%) (sciatic (2), -or peroneal nerve (6)). SCI patients had in average reduced motor unit number compared with HC and prolonged muscle refractory period and reduced supernormality.SignificanceA high prevalence of nerve lesion and a diffuse affection of the PNS following SCI are highly relevant findings that should be accounted for when planning neurorehabilitation for persons living with SCI.     

Spinal muscular atrophy type I mimicking critical illness neuropathy in a paediatric intensive care neonate: electrophysiological features

We report the case of a neonate with spinal muscular atrophy type I (SMA type I or Werdnig-Hoffman disease) who was initially misdiagnosis as having critical illness neuropathy. Electromyography (EMG) showed a moderate loss of voluntary and motor unit potentials of both neurogenic and myopathic appearance. Nerve conduction studies revealed the presence of a severe sensory-motor axonal neuropathy. Finally, a biopsy of quadriceps was compatible with the diagnosis of SMA type I. A genetic study confirmed the existence of a homozygous absence of exons 7 and 8 of the telomeric supervival motoneuron gene (SMN1 gene).     

MScanFit motor unit number estimation (MScan) and muscle velocity recovery cycle recordings in amyotrophic lateral sclerosis patients

ObjectiveMotor Unit Number Estimation (MUNE) methods, such as the recently developed MScanFit MUNE (MScan), may be valuable in tracking motor unit loss in ALS. Muscle Velocity Recovery Cycles (MVRCs) provide information about muscle membrane properties and can reveal disease-related changes.This study was undertaken to test the applicability of MScan to the anterior tibial muscle (TA) and to test whether the MVRCs could improve understanding of ALS pathophysiology.MethodsTwenty-six ALS patients and 25 healthy controls were evaluated by quantitative electromyography, nerve conduction study and the two novel methods: MScan and MVRC; all in the TA and peroneal nerve.ResultsThe estimated number of motor units for ALS patients (Median: 45, interquartile range: 28.5–76.5) was significantly lower than for the controls (117, 96.0–121.0) (P = 2.19 × 10⁻⁷). Unit size was increased only when amplitudes were expressed as percentage of CMAP. Of MVRC measurements, only relative refractory period was significantly abnormal in patients.ConclusionMScanFit MUNE gives a sensitive and quantitative measure of loss of TA motor units in ALS. Muscle fiber membrane properties are mostly unaffected, despite substantial denervation, presumably due to collateral reinnervation.SignificanceMScan is suitable for detecting motor unit loss in TA. MVRCs do not provide new insights in ALS.     

The role of potassium in muscle membrane dysfunction in end-stage renal disease

ObjectiveUremic myopathy is a condition seen in end-stage renal disease (ESRD), characterized by muscle weakness and muscle fatigue, in which the pathophysiology is uncertain. The aim of this study was to assess the role of abnormal serum constituents in ESRD patients by relating them to the excitability properties of the tibialis anterior muscle, at rest and during electrically induced muscle activation, by recording muscle velocity recovery cycles (MVRC) and frequency ramp responses.MethodsEighteen ESRD patients undergoing hemodialysis were evaluated by blood sample, MVRC, and frequency ramp (before and near the end of dialysis treatment), quantitative electromyography, and nerve conduction studies. Patients were compared to 24 control subjects.ResultsIn patients, muscle relative refractory period, early supernormality, late supernormality after 5 conditioning stimuli, and latency of the last of 15 and 30 frequency ramp pulses were strongly associated with potassium levels (p < 0.01), showing depolarization before and normalization in the end of hemodialysis.ConclusionsIn ESRD patients, the muscle membrane is depolarized, mainly due to hyperkalemia.SignificanceSince normal muscle fatigue has been attributed to potassium-induced depolarization, it seems likely that this mechanism is also a major cause of the exaggerated muscle fatigue and weakness in ESRD patients.     

Sarcolemmal depolarization in sporadic inclusion body myositis assessed with muscle velocity recovery cycles

ObjectiveTo study patients with sporadic inclusion body myositis (sIBM) with muscle velocity recovery cycles (MVRC) to assess muscle membrane excitability, pathophysiological mechanisms and potential biomarkers of this disorder.MethodsMVRC were recorded from 20 individuals with sIBM from tibialis anterior (TA) and rectus femoris (RF) muscles. Excitability parameters were compared with MVRC data obtained from 22 normal controls >50 years.ResultsMuscle relative refractory period was prolonged in both TA (6.4 ms vs 4.4 ms, P < 0.001) and RF (7.1 ms vs 3.9 ms, P < 0.001) of sIBM affected muscle when compared to controls. Early supernormality was reduced in both TA (3.6% vs 8.8% P = 0.001) and in RF (mean 5.4% vs 13% P < 0.001). Late supernormality was only decreased significantly in sIBM affected TA (1.8% vs 3.6% P = 0.001) but not in RF. No consistent correlations between MVRC parameters and clinical markers of sIBM disease severity were found.ConclusionThe resting sarcolemmal muscle membrane potential of sIBM muscle is depolarized relative to that of normal controls, which may be related to intramuscular amyloid deposition in sIBM.SignificanceSarcolemmal depolarization may play a role in muscle dysfunction and weakness observed in sIBM patients.