Respiratory muscle weakness in peripheral neuropathies

Chemogenetic stimulation of phrenic motor output and diaphragm activity

Impaired diaphragm activation contributes to morbidity and mortality in many neurodegenerative diseases and neurologic injuries. We conducted experiments to determine if expression of an excitatory DREADD (designer receptors exclusively activation by designer drugs) in the mid-cervical spinal cord would enable respiratory-related activation of phrenic motoneurons to increase diaphragm activation. Wild type (C57/bl6) and ChAT-Cre mice received bilateral intraspinal (C4) injections of an adeno-associated virus (AAV) encoding the hM3D(Gq) excitatory DREADD. In wild type mice, this produced non-specific DREADD expression throughout the mid-cervical ventral horn. In ChAT-Cre mice, a Cre-dependent viral construct was used to drive DREADD expression in C4 ventral horn motoneurons, targeting the phrenic motoneuron pool. Diaphragm EMG was recorded during spontaneous breathing at 6-8 weeks post-AAV delivery. The selective DREADD ligand JHU37160 (J60) caused a bilateral, sustained (>1 hr) increase in inspiratory EMG bursting in both groups; the relative increase was greater in ChAT-Cre mice. Additional experiments in a ChAT-Cre rat model were conducted to determine if spinal DREADD activation could increase inspiratory tidal volume (VT) during spontaneous breathing without anesthesia. Three to four months after intraspinal (C4) injection of AAV driving Cre-dependent hM3D(Gq) expression, intravenous J60 resulted in a sustained (>30 min) increase in VT assessed using whole-body plethysmography. Subsequently, direct nerve recordings confirmed that J60 evoked a >50% increase in inspiratory phrenic output. The data show that mid-cervical spinal DREADD expression targeting the phrenic motoneuron pool enables ligand-induced, sustained increases in the neural drive to the diaphragm. Further development of this technology may enable application to clinical conditions associated with impaired diaphragm activation and hypoventilation.

Guillain-Barré syndrome after surgery: a literature review

Guillain-Barré syndrome (GBS) is a rare postoperative complication that is sometimes characterized by serious motor weakness and prolonged weaning from mechanical ventilation. Although the exact nature of the relationship between GBS and the surgical procedure is still unclear, there is a clear increased incidence of GBS in post-surgical patients compared to non-surgical patients. GBS after surgery is unique in several ways. The course of post-surgical GBS unfolds more rapidly than in other situations where GBS develops, the condition is often more severe, and respiratory muscles are more commonly involved. Prompt diagnosis and appropriate treatment are essential, and the condition can worsen if treated inappropriately. Postoperative sedation, intubation, and restraint use make the diagnosis of GBS difficult, as the onset of symptoms of weakness or numbness in those contexts are not obvious. GBS is often misdiagnosed, being attributed to other postoperative complications, and subsequently mishandled. The lack of relevant information further obscures the clinical picture. We sought to better understand post-surgical GBS by performing an analysis of the relevant literature, focusing on clearly documenting the clinical characteristics, diagnosis, and management of GBS that emerges following surgery. We underscore the importance of physicians being aware of the possibility of GBS after major surgery and of performing a variety of laboratory clinical investigations early on in suspected cases.

Guillain-Barré Syndrome

OBJECTIVE

This article summarizes the clinical features, diagnostic criteria, differential diagnosis, pathogenesis, and prognosis of Guillain-Barré syndrome (GBS), with insights into the current and future diagnostic and therapeutic interventions for this neuromuscular syndrome.

LATEST DEVELOPMENTS

GBS is an acute, inflammatory, immune-mediated polyradiculoneuropathy that encompasses many clinical variants and divergent pathogenic mechanisms that lead to axonal, demyelinating, or mixed findings on electrodiagnostic studies. The type of antecedent infection, the development of pathogenic cross-reactive antibodies via molecular mimicry, and the location of the target gangliosides affect the subtype and severity of the illness. The data from the International GBS Outcome Study have highlighted regional variances, provided new and internationally validated prognosis tools that are beneficial for counseling, and introduced a platform for discussion of GBS-related open questions. New research has been undertaken, including research on novel diagnostic and therapeutic biomarkers, which may lead to new therapies.

ESSENTIAL POINTS

GBS is among the most frequent life-threatening neuromuscular emergencies in the world. At least 20% of patients with GBS have a poor prognosis and significant residual deficits despite receiving available treatments. Research is ongoing to further understand the pathogenesis of the disorder, find new biomarkers, and develop more effective and specific treatments.

Primary Cilia in Glial Cells: An Oasis in the Journey to Overcoming Neurodegenerative Diseases

Many neurodegenerative diseases have been associated with defects in primary cilia, which are cellular organelles involved in diverse cellular processes and homeostasis. Several types of glial cells in both the central and peripheral nervous systems not only support the development and function of neurons but also play significant roles in the mechanisms of neurological disease. Nevertheless, most studies have focused on investigating the role of primary cilia in neurons. Accordingly, the interest of recent studies has expanded to elucidate the role of primary cilia in glial cells. Correspondingly, several reports have added to the growing evidence that most glial cells have primary cilia and that impairment of cilia leads to neurodegenerative diseases. In this review, we aimed to understand the regulatory mechanisms of cilia formation and the disease-related functions of cilia, which are common or specific to each glial cell. Moreover, we have paid close attention to the signal transduction and pathological mechanisms mediated by glia cilia in representative neurodegenerative diseases. Finally, we expect that this field of research will clarify the mechanisms involved in the formation and function of glial cilia to provide novel insights and ideas for the treatment of neurodegenerative diseases in the future.

Diagnostic yield of advanced genetic testing in patients with hereditary neuropathies: A retrospective single-site study

INTRODUCTION/AIMS

Advanced genetic testing including next-generation sequencing (AGT/NGS) has facilitated DNA testing in the clinical setting and greatly expanded new gene discovery for the Charcot-Marie-Tooth neuropathies and other hereditary neuropathies (CMT/HN). Herein, we report AGT/NGS results, clinical findings, and diagnostic yield in a cohort of CMT/HN patients evaluated at our neuropathy care center.

METHODS

We reviewed the medical records of all patients with suspected CMT/HN who underwent AGT/NGS at the Hospital for Special Care from January 2017 through January 2020. Patients with variants reported as pathogenic or likely pathogenic were included for further clinical review.

RESULTS

We ordered AGT/NGS on 108 patients with suspected CMT/HN. Of these, pathogenic or likely pathogenic variants were identified in 17 patients (diagnostic yield, 15.7%), including 6 (35%) with PMP22 duplications; 3 (18%) with MPZ variants; 2 (12%) with MFN2 variants; and 1 each with NEFL, IGHMBP2, GJB1, BSCL2, DNM2, and TTR variants. Diagnostic yield increased to 31.0% for patients with a positive family history.

DISCUSSION

AGT/NGS panels can provide specific genetic diagnoses for a subset of patients with CMT/HN disorders, which improves disease and genetic counseling and prepares patients for disease-focused therapies. Despite these advancements, many patients with known or suspected CMT/HN disorders remain without a specific genetic diagnosis. Continued advancements in genetic testing, such as multiomic technology and better understanding of genotype-phenotype correlation, will further improve detection rates for patients with suspected CMT/HN disorders.

Intensive Care and Treatment of Severe Guillain-Barré Syndrome

Guillain–Barré syndrome (GBS) is an acute polyneuropathy mostly characterized by acute flaccid paralysis with or without sensory/autonomous nerve dysfunction. Current immuno therapies including intravenous immunoglobulin (IVIg), plasma exchange (PE), and newly developed biological drugs benefit patients by alleviating hyperreactive immune responses. Up to 30% of patients develop respiratory failure during hospitalization and require mechanical ventilation and intensive care. Immunotherapies, mechanical ventilation, supportive care, and complication management during the intensive care unit (ICU) stay are equally emphasized. The most important aspect of intensive care and treatment of severe GBS, that is, mechanical ventilation, has been extensively reviewed elsewhere. In contrast to immunotherapies, care and treatment of GBS in the ICU setting are largely empirical. In this review, we intend to stress the importance of intensive care and treatment, other than mechanical ventilation in patients with severe GBS. We summarize the up-to-date knowledge of pharmacological therapies and ICU management of patients with severe GBS. We aim to answer some key clinical questions related to the management of severe GBS patients including but not limited to: Is IVIg better than PE or vice versa? Whether combinations of immune therapies benefit more? How about the emerging therapies promising for GBS? When to perform tracheal intubation or tracheostomy? How to provide multidisciplinary supportive care for severe cases? How to avert life-threatening complications in severe cases?

Mechanical ventilation in Guillain-Barré syndrome

Introduction: Up to 30% of patients with Guillain-Barré syndrome (GBS) develop respiratory failure requiring intensive care unit (ICU) admission and mechanical ventilation. Progressive weakness of the respiratory muscles is the leading cause of acute respiratory distress and respiratory failure with hypoxia and/or hypercarbia. Bulbar weakness may compromise airway patency and predispose patients to aspiration pneumonia. Areas covered: Clinical questions related to the use of mechanical ventilation include but are not limited to: When to start? Invasive or noninvasive? When to wean from mechanical ventilation? When to perform tracheostomy? How to manage complications of GBS in the ICU including nosocomial infection, ventilator-associated pneumonia, and ICU-acquired weakness? In this narrative review, the authors summarize the up-to-date knowledge of the incidence, pathophysiology, evaluation, and general management of respiratory failure in GBS. Expert opinion: Respiratory failure in GBS merits more attention from caregivers. Emergency intubation may lead to life-threatening complications. Appropriate methods and time point of intubation and weaning, an early tracheostomy, and predictive prophylaxis of complications benefit patients' long-term prognosis.

Why Are Botulinum Neurotoxin-Producing Bacteria So Diverse and Botulinum Neurotoxins So Toxic?

Botulinum neurotoxins (BoNTs) are the most lethal toxins among all bacterial, animal, plant and chemical poisonous compounds. Although a great effort has been made to understand their mode of action, some questions are still open. Why, and for what benefit, have environmental bacteria that accidentally interact with their host engineered so diverse and so specific toxins targeting one of the most specialized physiological processes, the neuroexocytosis of higher organisms? The extreme potency of BoNT does not result from only one hyperactive step, but in contrast to other potent lethal toxins, from multi-step activity. The cumulative effects of the different steps, each having a limited effect, make BoNTs the most potent lethal toxins. This is a unique mode of evolution of a toxic compound, the high potency of which results from multiple steps driven by unknown selection pressure, targeting one of the most critical physiological process of higher organisms.

The neurology of acutely failing respiratory mechanics

Forces involved in breathing-which effectively pull in air-are the diaphragmatic, intercostal, spine, and neck muscles. Equally important is the bulbar musculature maintaining the architecture of a patent airway conduit and abdominal wall and internal intercostal muscles providing cough. Acute injury along a neural trajectory from brainstem to muscle will impair the coordinated interaction between these muscle groups. Acutely failing respiratory mechanics can be caused by central and peripheral lesions. In central lesions, the key lesion is in the nucleus ambiguus innervating the dilator muscles of the soft palate, pharynx, and larynx, but abnormal respiratory mechanics rarely coincide with abnormalities of the respiratory pattern generator. In peripheral lesions, diaphragmatic weakness is a main element, but in many neuromuscular disorders mechanical upper airway obstruction from oropharyngeal weakness contributes equally to an increased respiratory load. The neurology of breathing involves changes in respiratory drive, rhythm, mechanics, and dynamics. This review focuses on the fundamentals of abnormal respiratory mechanics in acute neurologic conditions, bedside judgment, interpretation of additional laboratory tests, and initial stabilization, with practical solutions provided. Many of these respiratory signs are relevant to neurologists, who in acute situations may see these patients first. Ann Neurol 2017;81:485-494.

Management of acute neuromuscular disorders

Imminent neuromuscular respiratory failure is recognized by shortness of breath, restlessness, and tachycardia and is often followed by tachypnea, constantly interrupting speech, asynchronous breathing and sometimes paradoxical breathing and use of scalene and sternocleidomastoid muscles. Once a patient presents with such a constellation of signs, there are some difficult decisions to be made and include assessment of the severity of respiratory failure and in particular when to intubate. Failure of the patient to manage secretions as a result of oropharyngeal weakness rather than neuromuscular respiratory weakness may be another reason for acute intubation. Any patient with rapidly worsening weakness on presentation will need admission and observation in an intensive care unit. This chapter summarizes the pathophysiology of acute neuromuscular respiratory failure, its clinical recognition and respiratory management and outcome expectations.

Cardiac Involvement in Peripheral Neuropathies

Cardiac autonomic neuropathy (CAN) is the least recognized and understood complication of peripheral neuropathy. However, because of its potential adverse effects including sudden death, CAN is one of the most important forms of autonomic neuropathies. CAN presents with different clinical manifestations including postural hypotension, exercise intolerance, fluctuation of blood pressure and heart rate, arrhythmia, and increased risk of myocardial infarction. In this article, the prevalence, clinical presentations, and management of cardiac involvement in certain peripheral neuropathies, including diabetic neuropathy, Guillain-Barré syndrome, chronic inflammatory polyneuropathy, human immunodeficiency virus-associated neuropathy, hereditary neuropathies, and amyloid neuropathy are examined in detail.

Evaluation of Respiratory Muscle Strength and Pulmonary Function in Patients with Charcot-Marie-Tooth Disease Type 2

The aim of this study was to evaluate the pulmonary condition in a large family with Charcot-Marie-Tooth disease type 2 (CMT2). Eighteen participants diagnosed with CMT2 and 20 healthy individuals were evaluated by spirometry and maximal expiratory and maximal inspiratory pressures (MEP and MIP, respectively). Clinical disability was measured with CMT neuropathy score (CMTNS; range 0-36). One control group (CG) comprising 20 individuals, matched for age, sex and body mass index, were used for comparison. Eight patients were female (44.5%) and 10 patients were male (55.5%); mean age was 31.8 years (range 11-79) and CMTNS range was 6-26. Differences between CMT2 and CG in the spirometry and respiratory muscle strength were statistically significant for all dimensions. There were significant correlations between CMTNS and MIP (Pearson = -0.581) and MEP (Pearson = -0.5090). The results of this study show that patients with CMT, in spite of not showing clinical signs of advanced respiratory impairment, may present subclinical respiratory changes. The respiratory comprise in the CMT disease can be silent and insidious without presenting characteristic clinical signals.

Inflammatory nodule mimicking a phrenic neoplasm

BACKGROUND AND AIMS

Isolated phrenic nerve nodule is usually a primitive tumour. Surgery is diagnostic and therapeutic at the same time. We report the case of a completely serum-negative Caucasian male with a right diaphragmatic relaxation associated to an isolated small nodule of the phrenic nerve.

METHODS

The patient was referred to our unit complaining shortness of breath and progressive fatigue. A standard chest X-ray showed right diaphragmatic palsy; chest scanning revealed a nodular lesion belonging to the right phrenic nerve. Positron emission tomography was negative for glucose uptake. The preoperative diagnosis of primitive neurogenic tumour was thus supposed, and the patient treated by the lesion's surgical resection along with diaphragmatic plication.

RESULT

Histopathological examination revealed an idiopathic inflammatory nodule of the phrenic nerve.

CONCLUSION

Such condition has not previously been reported in the literature among the possible aetiology of a diaphragmatic relaxation.