Timectomía transesternal extendida en pacientes con miastenia grave / Extended Transsternal Thymectomy in Patients with Myasthenia Gravis

Introducción: La miastenia grave adquirida es un trastorno de la transmisión neuromuscular, causado por la unión de autoanticuerpos con los componentes de la placa neuromuscular, más frecuentemente con el receptor de acetilcolina. Objetivo: Evaluar los resultados quirúrgicos inmediatos, obtenidos con la timectomía extendida en pacientes con miastenia grave timomatosa y no timomatosa. Métodos: Se realizó un estudio observacional, prospectivo y descriptivo para evaluar los resultados postoperatorios inmediatos de 21 pacientes intervenidos por miastenia grave entre junio de 2015 y mayo de 2020. Las variables estudiadas fueron edad, sexo, lesiones tímicas asociadas y resultados inmediatos: complicaciones y mortalidad ocurridas hasta 30 días de la intervención. Los datos fueron obtenidos de una base en Microsoft Access. Resultados: Dieciséis (76,2 por ciento) pertenecían al sexo femenino y 5 (23, 8 por ciento) al masculino. El mayor número correspondió a la MG con timoma, seguido por la MG e hiperplasia tímica (8) y uno con MG y restos tímicos. Se complicaron tres pacientes (14,3 por ciento). Uno presentó dos complicaciones: enfisema subcutáneo y septicemia, el siguiente, fiebre sin causa aparente y, el último, infección superficial de la herida. No hubo fallecidos. Conclusiones: La timectomía transesternal extendida permite extirpar el timo y la mayor parte de los tejidos adiposo y tímico aberrante, en el cuello y el mediastino. En pacientes tratados por equipos multidisciplinarios, con experiencia en esta cirugía, las complicaciones y la mortalidad tempranas usualmente son favorables(AU)

Introduction: Acquired myasthenia gravis (MG) is a neuromuscular transmission disorder caused by the union of autoantibodies and the components of the neuromuscular plaque, most frequently with the acetylcholine receptor. Objective: To assess the immediate surgical outcomes of extended thymectomy in patients with thymomatous and nonthymomatous myasthenia gravis. Methods: An observational, prospective and descriptive study was carried out to assess the immediate postoperative outcomes of 21 patients operated on for myasthenia gravis between June 2015 and May 2020. The variables studied were age, sex, associated thymic lesions, and immediate outcomes: complications and mortality that occurred up to thirty days after the intervention. The data were obtained from a Microsoft Access database. Results: Sixteen (76.2 percent) belonged to the female sex and five (23.8 percent) to the male sex. The highest number corresponded to MG with thymoma, followed by MG and thymic hyperplasia (8) and one with MG and thymic remains. Three patients (14.3 percent) were complicated. One had two complications: subcutaneous emphysema and septicemia; the next had unexplained fever; and the last one had superficial wound infection. There were no deaths. Conclusions: Extended transsternal thymectomy allows removal of the thymus and most of the adipose and aberrant thymic tissues in the neck and mediastinum. In patients treated by multidisciplinary teams, with experience in this surgery, outcomes regarding early complications and mortality are usually favorable(AU)

Reduced C9orf72 function leads to defective synaptic vesicle release and neuromuscular dysfunction in zebrafish.

The most common genetic cause of amyotrophic lateral sclerosis (ALS) and fronto-temporal dementia (FTD) is a hexanucleotide repeat expansion within the C9orf72 gene. Reduced levels of C9orf72 mRNA and protein have been found in ALS/FTD patients, but the role of this protein in disease pathogenesis is still poorly understood. Here, we report the generation and characterization of a stable C9orf72 loss-of-function (LOF) model in the zebrafish. We show that reduced C9orf72 function leads to motor defects, muscle atrophy, motor neuron loss and mortality in early larval and adult stages. Analysis of the structure and function of the neuromuscular junctions (NMJs) of the larvae, reveal a marked reduction in the number of presynaptic and postsynaptic structures and an impaired release of quantal synaptic vesicles at the NMJ. Strikingly, we demonstrate a downregulation of SV2a upon C9orf72-LOF and a reduced rate of synaptic vesicle cycling. Furthermore, we show a reduced number and size of Rab3a-postive synaptic puncta at NMJs. Altogether, these results reveal a key function for C9orf72 in the control of presynaptic vesicle trafficking and release at the zebrafish larval NMJ. Our study demonstrates an important role for C9orf72 in ALS/FTD pathogenesis, where it regulates synaptic vesicle release and neuromuscular functions.

Progressive Motor Deficit is Mediated by the Denervation of Neuromuscular Junctions and Axonal Degeneration in Transgenic Mice Expressing Mutant (P301S) Tau Protein.

Tauopathies include a variety of neurodegenerative diseases associated with the pathological aggregation of hyperphosphorylated tau, resulting in progressive cognitive decline and motor impairment. The underlying mechanism for motor deficits related to tauopathy is not yet fully understood. Here, we use a novel transgenic tau mouse line, Tau 58/4, with enhanced neuron-specific expression of P301S mutant tau to investigate the motor abnormalities in association with the peripheral nervous system. Using stationary beam, gait, and rotarod tests, motor deficits were found in Tau 58/4 mice already 3 months after birth, which deteriorated during aging. Hyperphosphorylated tau was detected in the cell bodies and axons of motor neurons. At the age of 9 and 12 months, significant denervation of the neuromuscular junction in the extensor digitorum longus muscle was observed in Tau 58/4 mice, compared to wild-type mice. Muscle hypotrophy was observed in Tau 58/4 mice at 9 and 12 months. Using electron microscopy, we observed ultrastructural changes in the sciatic nerve of 12-month-old Tau 58/4 mice indicative of the loss of large axonal fibers and hypomyelination (assessed by g-ratio). We conclude that the accumulated hyperphosphorylated tau in the axon terminals may induce dying-back axonal degeneration, myelin abnormalities, neuromuscular junction denervation, and muscular atrophy, which may be the mechanisms responsible for the deterioration of the motor function in Tau 58/4 mice. Tau 58/4 mice represent an interesting neuromuscular degeneration model, and the pathological mechanisms might be responsible for motor signs observed in some human tauopathies.

Preservation of neuromuscular function in symptomatic SOD1-G93A mice by peripheral infusion of methylene blue.

In mutant superoxide dismutase 1 (SOD1) mouse models of familial amyotrophic lateral sclerosis (fALS) some of the earliest signs of morphological and functional damage occur in the motor nerve terminals that innervate fast limb muscles. This study tested whether localized peripheral application of a protective drug could effectively preserve neuromuscular junctions in late-stage disease. Methylene blue (MB), which has mitochondria-protective properties, was infused via an osmotic pump into the anterior muscle compartment of one hind limb of late pre- symptomatic SOD1-G93A mice for ≥3weeks. When mice reached end-stage disease, peak twitch and tetanic contractions evoked by stimulation of the muscle nerve were measured in two anterior compartment muscles (tibialis anterior [TA] and extensor digitorum longus [EDL], both predominantly fast muscles). With 400µM MB in the infusion reservoir, muscles on the MB-infused side exhibited on average a ~100% increase in nerve-evoked contractile force compared to muscles on the contralateral non-infused side (p<0.01 for both twitch and tetanus in EDL and TA). Pairwise comparisons of endplate innervation also revealed a beneficial effect of MB infusion, with an average of 65% of endplates innervated in infused EDL, compared to only 35% on the non-infused side (p<0.01). Results suggested that MB's protective effects required an extracellular [MB] of ~1µM, were initiated peripherally (no evidence of retrograde transport into the spinal cord), and involved MB's reduced form. Thus peripherally-initiated actions of MB can help preserve neuromuscular structure and function in SOD1-G93A mice, even at late stages of disease.

Neuromuscular junction degeneration in muscle wasting.

PURPOSE OF REVIEW: Denervation is a hallmark of age-related and other types of muscle wasting. This review focuses on recent insights and current viewpoints regarding the mechanisms and clinical relevance of maintaining the neuromuscular junction to counteract muscle wasting resulting from aging or neural disease/damage. RECENT FINDINGS: Activity-dependent regulation of autophagy, the agrin-muscle specific kinase-Lrp4 signaling axis, and sympathetic modulation are principal mechanisms involved in stabilizing the neuromuscular junction. These findings are derived from several animal models and were largely confirmed by human gene expression analysis as well as insights from rare neuromuscular diseases such as amyotrophic lateral sclerosis and congenital myasthenic syndromes. Based on these insights, agrin-derived fragments are currently being evaluated as biomarkers for age-related muscle wasting. Tuning of autophagy, of the agrin pathway, and of sympathetic input are being studied as clinical treatment of muscle wasting disorders. SUMMARY: Basic research has revealed that maintenance of neuromuscular junctions and a few signaling pathways are important in the context of age-dependent and other forms of muscle wasting. These findings have recently started to enter clinical practice, but further research needs to substantiate and refine our knowledge.

Structural and Functional Abnormalities of the Neuromuscular Junction in the Trembler-J Homozygote Mouse Model of Congenital Hypomyelinating Neuropathy.

Mutations in peripheral myelin protein 22 (PMP22) result in the most common form of Charcot-Marie-Tooth (CMT) disease, CMT1A. This hereditary peripheral neuropathy is characterized by dysmyelination of peripheral nerves, reduced nerve conduction velocity, and muscle weakness. APMP22 point mutation in L16P (leucine 16 to proline) underlies a form of human CMT1A as well as the Trembler-J mouse model of CMT1A. Homozygote Trembler-J mice (Tr(J)) die early postnatally, fail to make peripheral myelin, and, therefore, are more similar to patients with congenital hypomyelinating neuropathy than those with CMT1A. Because recent studies of inherited neuropathies in humans and mice have demonstrated that dysfunction and degeneration of neuromuscular synapses or junctions (NMJs) often precede impairments in axonal conduction, we examined the structure and function of NMJs in Tr(J)mice. Although synapses appeared to be normally innervated even in end-stage Tr(J)mice, the growth and maturation of the NMJs were altered. In addition, the amplitudes of nerve-evoked muscle endplate potentials were reduced and there was transmission failure during sustained nerve stimulation. These results suggest that the severe congenital hypomyelinating neuropathy that characterizes Tr(J)mice results in structural and functional deficits of the developing NMJ.

LMO7-null mice exhibit phenotypes consistent with emery-dreifuss muscular dystrophy.

INTRODUCTION: Mutations in the inner nuclear envelope protein emerin cause Emery-Dreifuss muscular dystrophy (EDMD), which is characterized by progressive skeletal muscle wasting, cardiac conduction defects, and tendon contractures. We previously showed that emerin binds directly to the transcription regulator Lmo7 and attenuates its activity to regulate the proper temporal expression of important myogenic differentiation genes. METHODS: The skeletal muscle and cardiac phenotypes were analyzed in a newly generated Lmo7-null mouse using histological analysis, echocardiography, and various neuromuscular tests to determine if Lmo7 was important for skeletal muscle and cardiac function. RESULTS: Lmo7-null mice had growth retardation, decreased fiber size, and impaired skeletal muscle and cardiac function. Lmo7-null mice also had lower levels of phosphorylated retinoblastoma (Rb), extracellular signal-regulated kinase, and c-Jun N-terminal kinase, which is consistent with altered Rb and mitogen-activated protein kinase signaling. CONCLUSIONS: These findings demonstrate that loss of Lmo7 in mice causes myopathic phenotypes similar to those seen in other EDMD mouse models.

Manual stimulation of the whisker pad after hypoglossal-facial anastomosis (HFA) using a Y-tube conduit does not improve recovery of whisking function.

Facial nerve injury is a common clinical trauma involving long-term functional deficits with facial asymmetry leading to associated psychological issues and social hardship. We have recently shown that repair by hypoglossal-facial or facial-facial nerve surgical end-to-end anastomosis and suture [hypoglossal-facial anastomosis (HFA) or facial-facial anastomosis (FFA)] results in collateral axonal branching, polyinnervation of neuromuscular junctions (NMJs) and poor function. We have also shown that another HFA repair procedure using an isogenic Y-tube (HFA + Y-tube) and involving a 10-mm gap reduces collateral axonal branching, but fails to reduce polyinnervation. Furthermore, we have previously demonstrated that manual stimulation (MS) of facial muscles after FFA or HFA reduces polyinnervation of NMJs and improves functional recovery. Here, we examined whether HFA + Y-tube and MS of the vibrissal muscles reduce polyinnervation and restore function. Isogenic Y-tubes were created using abdominal aortas. The proximal hypoglossal nerve was inserted into the long arm and sutured to its wall. The distal zygomatic and buccal facial nerve branches were inserted into the two short arms and likewise sutured to their walls. Manual stimulation involved gentle stroking of the vibrissal muscles by hand mimicking normal whisker movement. We evaluated vibrissal motor performance using video-based motion analysis, degree of collateral axonal branching using double retrograde labeling and the quality of NMJ reinnervation in target musculature using immunohistochemistry. MS after HFA + Y-tube reduced neither collateral branching, nor NMJ polyinnervation. Accordingly, it did not improve recovery of function. We conclude that application of MS after hypoglossal-facial nerve repair using an isogenic Y-tube is contraindicated: it does not lead to functional recovery but, rather, worsens it.

Botulism in children: a diagnostic dilemma in developing countries.

Botulism is a well-known disease of the neuromuscular junction. It is a rare but curable cause of paralysis in paediatric population. In addition to classical clinical signs and symptoms, the diagnosis of botulism requires laboratory confirmation of intoxication by various biological tests. These include demonstration of botulinum toxin in serum or isolation of the Clostridium botulinum from stool/gastric aspirates. However, it is not always possible to confirm intoxication due to unavailability of technical facilities, especially in resource limited countries like Pakistan. Under these circumstances, electrophysiological studies serve as an excellent diagnostic tool. These studies can provide quick diagnosis of botulism so that early administration of botulism immunoglobulin, if available, can reduce morbidity, mortality and length of stay in hospital. We report a case of botulism from Pakistan diagnosed on the basis of electrophysiological studies.

Dysfunction of the neuromuscular junction in spinal muscular atrophy types 2 and 3.

OBJECTIVE: Spinal muscular atrophy (SMA) is pathologically characterized by degeneration of anterior horn cells. Recent observations in animal models of SMA and muscle tissue from patients with SMA suggest additional abnormalities in the development and maturation of the neuromuscular junction. We therefore evaluated neuromuscular junction function in SMA with repetitive nerve stimulation. METHODS: In this case-control study, repetitive nerve stimulation was performed in 35 patients with SMA types 2, 3, and 4, 20 healthy controls, and 5 controls with motor neuron disease. RESULTS: Pathologic decremental responses (>10%) during 3-Hz repetitive nerve stimulation were observed in 17 of 35 patients (49%) with SMA types 2 and 3, but not in healthy controls or controls with motor neuron disease. None of the patients or controls had an abnormal incremental response of >60%. The presence of an abnormal decremental response was not specific for the type of SMA, nor was it associated with compound muscle action potential amplitude, clinical scores, or disease duration. Two of 4 patients with SMA type 3 who tried pyridostigmine reported increased stamina. CONCLUSIONS: These data suggest dysfunction of the neuromuscular junction in patients with SMA types 2 and 3. Therefore, drugs that facilitate neuromuscular transmission are candidate drugs for evaluation in carefully designed, placebo-controlled, clinical trials.

Neuromuscular abnormality and autonomic dysfunction in patients with cerebrotendinous xanthomatosis.

BACKGROUND: Cerebrotendinous xanthomatosis (CTX) is a rare lipid-storage disease. Neuromuscular abnormality and autonomic system (ANS) dysfuction in CTX are rarely examined in large-scale studies in the literature. We studied the peripheral nervous system, myopathology, and autonomic system of four CTX patients and performed a literature review of the reported CTX patients with peripheral neuropathy. METHODS: Four biochemically and genetically confirmed CTX patients, belonging to two families, were included for study and all received nerve conduction study (NCS), muscle biopsy for histopathologic and ultrastructural study, skin biopsy for intraepidermal nerve fiber (INEF) density measurement, autonomic testings including sympathetic skin response, R-R interval variation and head-up tilt test using an automated tilt table to record the changes of blood pressure and heart rate in different postures. The Q-Sweat test was also applied for the detection of sweat amount and onset time of response. The clinical characteristics, study methods and results of 13 studies of peripheral neuropathy in CTX patients in the literature were also recorded for analysis. RESULTS: The results of NCS study showed axonal sensory-motor polyneuropathy in three CTX cases and mixed axonal and demyelinating sensor-motor polyneuropathy in one. The myopathological and histopathologic studies revealed mild denervation characteristics, but the ultrastructural study revealed changes of mitochondria and the membranous system, and increased amounts of glycogen, lipofuscin and lipid deposition. The ANS study revealed different degrees of abnormalities in the applied tests and the INEF density measurement showed small fiber neuropathy in three of the four CTX patients. The literature review of peripheral neuropathy in CTX revealed different types of peripheral neuropathy, of which axonal peripheral neuropathy was the most common. CONCLUSIONS: Peripheral neuropathy, especially the subtype of axonal sensori-motor neuropathy, is common in patients with CTX. Evidence of lipid metabolic derangement in CTX can be reflected in ultrastructural studies of muscles. With an adequate multi-parametric evaluation, a high incidence of ANS abnormalities can be seen in this rare lipid-storage disease, and a high incidence of small fiber involvement is also reflected in the IENF density measurement of skin biopsies.

Defective neuromuscular junction organization and postnatal myogenesis in mice with severe spinal muscular atrophy.

A detailed pathologic analysis was performed on Smn(-/-);SMN2 mice as a mouse model for human type I spinal muscular atrophy (SMA). We provide new data concerning changes in the spinal cord, neuromuscular junctions and muscle cells, and in the organs of the immune system. The expression of 10 synaptic proteins was analyzed in 3-dimensionally reconstructed neuromuscular junctions by confocal microscopy. In addition to defects in postsynaptic occupancy, there was a marked reduction in calcitonin gene-related peptide and Rab3A in the presynaptic motor terminals of some, but not all, of the skeletal muscles analyzed. Defects in the organization of presynaptic nerve terminals were also detected by electron microscopy. Moreover, degenerative changes in muscle cells, defective postnatal muscle growth, and prominent muscle satellite cell apoptosis were also observed. All of these changes occurred in the absence of massive loss of spinal cord motoneurons. On the other hand, astroglia, but not microglia, increased in the ventral horn of newborn SMA mice. In skeletal muscles, the density of interstitial macrophages was significantly reduced, and monocyte chemotactic protein-1 was downregulated. These findings raise questions regarding the primary contribution of a muscle cell defect to the SMA phenotype.

Paraneoplastic muscle disease.

In paraneoplastic muscle disease, the malignancy may remotely affect neuromuscular transmission or incite muscle inflammation or necrosis. In several of these diseases, an autoimmune basis for the muscle disease has been established and has become a defining feature. These paraneoplastic muscle diseases may be the first manifestation of a malignancy, and their diagnosis thus demands a vigilant search for an underlying tumor. This article is focused on inflammatory and necrotizing myopathies and disorders of neuromuscular transmission that may arise in the setting of malignancy and are considered paraneoplastic phenomena.

Concurrent chronic motor axonal polyneuropathy and synaptic impairment of neuromuscular junction.

Polyneuropathies may exhibits clinical, electrophysiologic signs of neuromuscular junction impairment. Distal motor nerve terminals and neuromuscular junction contain pre or postsynaptically specific targets for circulating autoantibodies, if present in neuropathies. Motor nerve terminal blockade either reversible or permanent is a putative factor of muscle weakness. A 59-year-old patient exhibited oropharyngeal, facial, extremity weakness, fluctuating fatigability, and areflexia. Elecectrophysiologic studies showed purely motor axonal polyneuropathy. Thenar, facial slow rate repetitive stimulation revealed up to 47% decrement of compound muscle action potential size. Single fiber electromyography on voluntary activation confirmed increased jitter and impulse blocking in all muscles examined in one third of the fibers. Repeated testings for antibodies to gangliosides, acetylcholine, muscle tyrosine kinase receptors, voltage-gated calcium channels were negative. Oral pyridostigmine bromide improved bulbar symptoms. Pulse intravenous immunoglobulin, oral steroids, and azathioprine had steady benefit. Impairment of neuromuscular transmission if occurring in chronic axonal neuropathies highlights mechanisms and significance of neuromuscular chronic "synaptopathies."

Impairment of diaphragm muscle force and neuromuscular transmission after normothermic cardiopulmonary bypass: effect of low-dose inhaled CO.

Cardiopulmonary bypass (CPB) is associated with significant postoperative morbidity, but its effects on the neuromuscular system are unclear. Recent studies indicate that even relatively short periods of mechanical ventilation result in significant neuromuscular effects. Carbon monoxide (CO) has gained recent attention as therapy to reduce the deleterious effects of CPB. We hypothesized that 1) CPB results in impaired neuromuscular transmission and reduced diaphragm force generation; and 2) CO treatment during CPB will mitigate these effects. In adult male Sprague-Dawley rats, diaphragm muscle-specific force and neuromuscular transmission properties were measured 90 min after weaning from normothermic CPB (1 h). During CPB, either low-dose inhaled CO (250 ppm) or air was administered. The short period of mechanical ventilation used in the present study ( approximately 3 h) did not adversely affect diaphragm muscle contractile properties or neuromuscular transmission. CPB elicited a significant decrease in isometric diaphragm muscle-specific force compared with time-matched, mechanically ventilated rats ( approximately 25% decline in both twitch and tetanic force). Diaphragm muscle fatigability to 40-Hz repetitive stimulation did not change significantly. Neuromuscular transmission failure during repetitive activation was 60 +/- 2% in CPB animals compared with 76 +/- 4% in mechanically ventilated rats (P < 0.05). CO treatment during CPB abrogated the neuromuscular effects of CPB, such that diaphragm isometric twitch force and neuromuscular transmission were no longer significantly different from mechanically ventilated rats. Thus, CPB has important detrimental effects on diaphragm muscle contractility and neuromuscular transmission that are largely mitigated by CO treatment. Further studies are needed to ascertain the underlying mechanisms of CPB-induced neuromuscular dysfunction and to establish the potential role of CO therapy.

Novel anti-idiotype antibody therapy for lipooligosaccharide-induced experimental autoimmune neuritis: use relevant to Guillain-Barré syndrome.

Campylobacteriosis is a frequent antecedent event in Guillain-Barré syndrome (GBS), inducing high-titer serum antibodies for ganglioside antigens in the peripheral nervous system (PNS). Molecular mimicry between the lipooligosaccharide (LOS) component of Campylobacter jejuni and human peripheral nerve gangliosides is believed to play an important role in the pathogenesis of GBS. Conventional treatment strategies for patients with GBS include plasmapheresis, intravenous immunoglobulin (IVIG), and immunosuppression, which are invasive or relatively ineffective. In this study, we used our animal model of GBS, in which Lewis rats were immunized with GD3-like LOS isolated from C.jejuni. The animals developed anti-GD3 ganglioside antibodies and manifested neuromuscular dysfunction. To develop novel therapeutic strategies, we treated the animals by intraperitoneal administration of an anti-GD3 antiidiotype monoclonal antibody (BEC2) that specifically interacts with the pathogenic antibody. The treated animals had a remarkable reduction of anti-GD3 antibody titers and improvement of motor nerve functions. The results suggest that ganglioside mimics, such as antiidiotype antibodies, may be powerful reagents for therapeutic intervention in GBS by neutralizing specific pathogenic antiganglioside antibodies.

A review of autoimmune diseases associated with cancer.

The focus of this review is on the relationships between autoimmune diseases and cancer from two closely related perspectives: 1.Those autoimmune diseases which are often associated with malignancies. 2.Those prevalent cancers which may increase the risks of developing autoimmune disorders. The review concludes with a brief discussion of some selected innovative approaches to cancer immunotherapy.