Latrotoxin-Induced Neuromuscular Junction Degeneration Reveals Urocortin 2 as a Critical Contributor to Motor Axon Terminal Regeneration.

We used α-Latrotoxin (α-LTx), the main neurotoxic component of the black widow spider venom, which causes degeneration of the neuromuscular junction (NMJ) followed by a rapid and complete regeneration, as a molecular tool to identify by RNA transcriptomics factors contributing to the structural and functional recovery of the NMJ. We found that Urocortin 2 (UCN2), a neuropeptide involved in the stress response, is rapidly expressed at the NMJ after acute damage and that inhibition of CRHR2, the specific receptor of UCN2, delays neuromuscular transmission rescue. Experiments in neuronal cultures show that CRHR2 localises at the axonal tips of growing spinal motor neurons and that its expression inversely correlates with synaptic maturation. Moreover, exogenous UCN2 enhances the growth of axonal sprouts in cultured neurons in a CRHR2-dependent manner, pointing to a role of the UCN2-CRHR2 axis in the regulation of axonal growth and synaptogenesis. Consistently, exogenous administration of UCN2 strongly accelerates the regrowth of motor axon terminals degenerated by α-LTx, thereby contributing to the functional recovery of neuromuscular transmission after damage. Taken together, our results posit a novel role for UCN2 and CRHR2 as a signalling axis involved in NMJ regeneration.

Toxin-Induced Channelopathies, Neuromuscular Junction Disorders, and Myopathy.

Channelopathies, neuromuscular junction disorders, and myopathies represent multiple mechanisms by which toxins can affect the peripheral nervous system. These toxins include ciguatoxin, tetrodotoxin, botulinum toxin, metabolic poisons, venomous snake bites, and several medications. These toxins are important to be aware of because they can lead to serious symptoms, disability, or even death, and many can be treated if recognized ear.

Colistin-induced myasthenic syndrome in a patient with end-stage renal disease.

With resurgence of multidrug resistance (MDR) bacteria and no new novel broad-spectrum antibiotic in research pipeline, usage of older generation antibiotics, once discarded due to their toxicity profile are becoming popular again. Often these drugs are the only option left in managing MDR bacteria-related sepsis. Colistin is one of such antibiotic which is often used in recent times after decades of its avoidance due to its diverse toxicity profile. In this case report, we present a rare myasthenic syndrome like neuromuscular complication developed in a patient after receiving colistin for treatment of MDR Klebsiella-related urosepsis.

The RECITE Study: A Canadian Prospective, Multicenter Study of the Incidence and Severity of Residual Neuromuscular Blockade.

BACKGROUND: Postoperative residual neuromuscular blockade (NMB), defined as a train-of-four (TOF) ratio of <0.9, is an established risk factor for critical postoperative respiratory events and increased morbidity. At present, little is known about the occurrence of residual NMB in Canada. The RECITE (Residual Curarization and its Incidence at Tracheal Extubation) study was a prospective observational study at 8 hospitals in Canada investigating the incidence and severity of residual NMB. METHODS: Adult patients undergoing open or laparoscopic abdominal surgery expected to last <4 hours, ASA physical status I-III, and scheduled for general anesthesia with at least 1 dose of a nondepolarizing neuromuscular blocking agent for endotracheal intubation or maintenance of neuromuscular relaxation were enrolled in the study. Neuromuscular function was assessed using acceleromyography with the TOF-Watch SX. All reported TOF ratios were normalized to the baseline values. The attending anesthesiologist and all other observers were blinded to the TOF ratio (T4/T1) results. The primary and secondary objectives were to determine the incidence and severity of residual NMB (TOF ratio <0.9) just before tracheal extubation and at arrival at the postanesthesia care unit (PACU). RESULTS: Three hundred and two participants were enrolled. Data were available for 241 patients at tracheal extubation and for 207 patients at PACU arrival. Rocuronium was the NMB agent used in 99% of cases. Neostigmine was used for reversal of NMB in 73.9% and 72.0% of patients with TE and PACU data, respectively. The incidence of residual NMB was 63.5% (95% confidence interval, 57.4%-69.6%) at tracheal extubation and 56.5% (95% confidence interval, 49.8%-63.3%) at arrival at the PACU. In an exploratory analysis, no statistically significant differences were observed in the incidence of residual NMB according to gender, age, body mass index, ASA physical status, type of surgery, or comorbidities (all P > 0.13). CONCLUSIONS: Residual paralysis is common at tracheal extubation and PACU arrival, despite qualitative neuromuscular monitoring and the use of neostigmine. More effective detection and management of NMB is needed to reduce the risks associated with residual NMB.

Reversal of Pipecuronium-Induced Moderate Neuromuscular Block with Sugammadex in the Presence of a Sevoflurane Anesthetic: A Randomized Trial.

BACKGROUND: Pipecuronium is a steroidal neuromuscular blocking agent. Sugammadex, a relaxant binding γ-cyclodextrin derivative, reverses the effect of rocuronium, vecuronium, and pancuronium. We investigated whether sugammadex reverses moderate pipecuronium-induced neuromuscular blockade (NMB) and the doses required to achieve reversal. METHODS: This single-center, randomized, double-blind, 5-group parallel-arm study comprised 50 patients undergoing general anesthesia with propofol, sevoflurane, fentanyl, and pipecuronium. Neuromuscular monitoring was performed with acceleromyography (TOF-Watch SX) according to international standards. When the NMB recovered spontaneously to train-of-four count 2, patients randomly received 1.0, 2.0, 3.0, or 4.0 mg/kg of sugammadex or placebo. Recovery time from sugammadex injection to normalized train-of-four (TOF) ratio 0.9 was the primary outcome variable. The recovery time from the sugammadex injection to final T1 was the secondary end point. Postoperative neuromuscular functions were also assessed. RESULTS: Each patient who received sugammadex recovered to a normalized TOF ratio of 0.9 within 5.0 minutes (95% lower confidence interval for the lowest dose 70.1%; for all doses 90.8%) and 79% of these patients reached a normalized TOF ratio 0.9 within 2.0 minutes (95% lower confidence interval for the lowest dose 26.7%; for all doses 63.7%). T1 recovered several minutes after the TOF ratio. No residual postoperative NMB was observed. CONCLUSIONS: Sugammadex adequately and rapidly reverses pipecuronium-induced moderate NMB during sevoflurane anesthesia. Once the train-of-four count has spontaneously returned to 2 responses following pipecuronium administration, a dose of 2.0 mg/kg of sugammadex is sufficient to reverse the NMB.

Chronic proximal axonopathy in rats is associated with long-standing neurofilament depletion in neuromuscular junctions and behavioral deficits.

In rodents exposed to 3,3'-iminodipropionitrile (IDPN), neurofilaments (NFs) accumulate in swollen proximal axon segments; this also occurs in motor neurons of patients with amyotrophic lateral sclerosis. We hypothesized that early loss of NFs in neuromuscular junctions (NMJs) in IDPN proximal neuropathy would result in neuromuscular dysfunction and lead to neuromuscular detachment. Adult male rats were given 0 or 15 mmol/L IDPN in drinking water for up to 1 year. The IDPN-exposed rats dragged their tails and had impaired endurance in a grip test. Neuromuscular junctions and distal axons were examined in the levator auris longus muscle after 3, 6, 9, and 12 months. Neuromuscular junctions showed a progressive reduction in NF immunolabeling, which became undetectable in up to 70% of the NMJs after 12 months. Neurofilament labeling was also reduced in preterminal axons and in a more proximal axon level within the muscle. Triple-label analysis with antisyntaxin demonstrated that the terminals remained in place and usually contained a few minute NF bundles. Electron microscopy revealed the disappearance of terminal NFs, reduced content in synaptic vesicles, and accumulation of multilamellar bodies, but scant degeneration. Thus, IDPN proximal neurofilamentous axonopathy is associated with NF depletion in motor terminals; motor weakness and structural changes in the NMJs suggest impaired synaptic function despite long-term preservation of the NMJs.

Neuromuscular impairments in adult survivors of childhood acute lymphoblastic leukemia: associations with physical performance and chemotherapy doses.

BACKGROUND: Treatment regimens for childhood acute lymphoblastic leukemia (ALL) contain neurotoxic agents that may interfere with neuromuscular health. In this study, the authors examined associations between neuromuscular impairments and physical function and between neuromuscular impairments and doses of vincristine and intrathecal methotrexate used to treat leukemia among survivors of childhood ALL. METHODS: ALL survivors >10 years from diagnosis participated in neuromuscular performance testing. Treatment data were abstracted from medical records. Regression models were used to evaluate associations between treatment factors, neuromuscular impairments, and physical performance. RESULTS: Among 415 survivors (median age, 35 years; age range, 21-52 years), balance, mobility, and 6-minute walk (6MW) distances were 1.3 standard deviations below age-specific and sex-specific values in 15.4%, 3.6%, and 46.5% of participants, respectively. Impairments included absent Achilles tendon reflexes (39.5%), active dorsiflexion range of motion (ROM) <5 degrees (33.5%), and impaired knee extension strength (30.1%). In adjusted models (including cranial radiation), survivors who received cumulative intrathecal methotrexate doses ≥215 mg/m(2) were 3.4 times more likely (95% confidence interval, 1.2-9.8 times more likely) to have impaired ROM than survivors who received no intrathecal methotrexate, and survivors who received cumulative vincristine doses ≥39 mg/m(2) were 1.5 times more likely (95% CI, 1.0-2.5 times more likely) to have impaired ROM than survivors who received lower cumulative doses of vincristine. Higher intrathecal methotrexate doses were associated with reduced knee extension strength and 6MW distances. CONCLUSIONS: Neuromuscular impairments were prevalent in childhood ALL survivors and interfered with physical performance. Higher cumulative doses of vincristine and/or intrathecal methotrexate were associated with long-term neuromuscular impairments, which have implications on future function as these survivors age.

The spectrum of intermediate syndrome following acute organophosphate poisoning: a prospective cohort study from Sri Lanka.

BACKGROUND: Intermediate syndrome (IMS) is a major cause of death from respiratory failure following acute organophosphate poisoning. The objective of this study was to determine repetitive nerve stimulation (RNS) predictors of IMS that would assist in patient management and clinical research. METHODS AND FINDINGS: Seventy-eight consenting symptomatic patients with organophosphate poisoning were assessed prospectively with daily physical examination and RNS. RNS was done on the right and left median and ulnar nerves at 1, 3, 10, 15, 20, and 30 Hz. The study was conducted as a prospective observational cohort study in the Central Province, Sri Lanka. IMS was diagnosed in ten out of 78 patients using a priori clinical diagnostic criteria, and five of them developed respiratory failure. All ten patients showed progressive RNS changes correlating with the severity of IMS. A decrement-increment was observed at intermediate and high frequencies preceding the onset of clinical signs of IMS. As the patient developed clinical signs of IMS, decrement-increment was progressively noted at low and intermediate frequencies and a combination of decrement-increment and repetitive fade or severe decrement was noted at high frequencies. Severe decrement preceded respiratory failure in four patients. Thirty patients developed forme fruste IMS with less severe weakness not progressing to respiratory failure whose RNS was characterized by decrement-increment or a combination of decrement-increment and repetitive fade but never severe decrements. CONCLUSIONS: Characteristic changes in RNS, preceding the development of IMS, help to identify a subgroup of patients at high risk of developing respiratory failure. The forme fruste IMS with the characteristic early changes on RNS indicates that IMS is a spectrum disorder. RNS changes are objective and precede the diagnosis and complications of IMS. Thus they may be useful in clinical management and research.

Intermediate syndrome following organophosphate insecticide poisoning.

Acute organophosphate insecticide poisoning can manifest 3 different phases of toxic effects, namely, acute cholinergic crisis, intermediate syndrome (IMS), and delayed neuropathy. Among them, IMS has been considered as a major contributing factor of organophosphate-related morbidity and mortality because of its frequent occurrence and probable consequence of respiratory failure. Despite a high incidence, the pathophysiology that underlies IMS remains unclear. Previously proposed mechanisms of IMS include different susceptibility of various cholinergic receptors, muscle necrosis, prolonged acetylcholinesterase inhibition, inadequate oxime therapy, downregulation or desensitization of postsynaptic acetylcholine receptors, failure of postsynaptic acetylcholine release, and oxidative stress-related myopathy. The clinical manifestations of IMS typically occur within 24 to 96 hours, affecting conscious patients without cholinergic signs, and involve the muscles of respiration, proximal limb muscles, neck flexors, and muscles innervated by motor cranial nerves. With appropriate therapy that commonly includes artificial respiration, complete recovery develops 5-18 days later. Patients with atypical manifestations of IMS, especially a relapse or a continuum of acute cholinergic crisis, however, were frequently reported in clinical studies of IMS. The treatment of IMS is mainly supportive. Nevertheless, because IMS generally concurs with severe organophosphate toxicity and persistent inhibition of acetylcholinesterase, early aggressive decontamination, appropriate antidotal therapy, and prompt institution of ventilatory support should be helpful in ameliorating the magnitude and/or the incidence of IMS. Although IMS is well recognized as a disorder of neuromuscular junctions, its exact etiology, incidence, and risk factors are not clearly defined because existing studies are largely small-scale case series and do not employ a consistent and rigorous definition of IMS. Without a clear understanding of the pathophysiology of IMS, specific therapy is not available. The prognosis of IMS, however, is likely to be favorable if respiratory failure can be promptly recognized and treated accordingly.

Functional recovery after neuromuscular blockade in mechanically ventilated critically ill patients.

BACKGROUND: An estimated 24% to 70% of individuals have prolonged paralysis or severe weakness after receiving neuromuscular blocking agents (NMBAs) when therapy is terminated. OBJECTIVES: The purposes of this study were to (1) evaluate the relationship between recovery of neuromuscular transmission (NMT) and functional muscle activity after NMBA administration; (2) evaluate the relationship between delayed recovery of NMT or muscle activity and functional performance; and (3) determine the predictors of delayed recovery of NMT, muscle activity, and functional performance. METHODS: This was a multisite study using a prospective, nonexperimental, descriptive design with convenience sampling techniques. Instruments used included a five-point muscle score, Actigraph, and peripheral nerve stimulator. RESULTS: Key findings were as follows: (1) NMT returned promptly, whereas muscle activity remained severely depressed; (2) only two subjects (5%) recovered functional performance within 24 hours; (3) degree of muscle weakness immediately after neuromuscular blockade was associated with prolonged time to extubation and mobility; and (4) predictors of delayed recovery included cumulative dose of aminosteroid NMBAs, age, and renal function. CONCLUSION: Prolonged recovery of muscle activity and extreme weakness may occur despite brisk recovery of NMT after neuromuscular blockade.

Assessment of a simple artificial neural network for predicting residual neuromuscular block.

BACKGROUND: Postoperative residual curarization (PORC) after surgery is common and its detection has a high error rate. Artificial neural networks are being used increasingly to examine complex data. We hypothesized that a neural network would enhance prediction of PORC. METHODS: In 40 previously reported patients, neuromuscular function, neuromuscular block/antagonist usage and time intervals were recorded throughout anaesthesia until tracheal extubation by an observer uninvolved in patient care. PORC was defined as significant 'fade' (train of four <0.7) at extubation. Neuromuscular function was classified as PORC (value=1) or no PORC (value=0). A back-propagation neural network was trained to assign similar values (0, 1) for prediction of PORC, by examining the impact of (i) the degree of spontaneous recovery at reversal, and (ii) the time since pharmacological reversal, using the jackknife method. Successful prediction was defined as attainment of a predicted value within 0.2 of the target value. RESULTS: Twenty-six patients (65%) had PORC at tracheal extubation. Clinical detection of PORC had a sensitivity of 0 and specificity of 1, with an indeterminate positive predictive value and a negative predictive value of 0.35. Using the artificial neural network, one patient with residual block and one with adequate neuromuscular function were incorrectly classified during the test phase, with no indeterminate predictions, giving an artificial neural network sensitivity of 0.96 (chi(2)=44, P<0.001) and specificity of 0.92 (P=1), with a positive predictive value of 0.96 and a negative predictive value of 0.93 (chi(2)=12, P<0.001). CONCLUSIONS: Neural network-based prediction, using readily available clinical measurements, is significantly better than human judgement in predicting recovery of neuromuscular function.

Critical illness neuromuscular abnormalities.

CINMAs occur commonly in acutely critically ill inflamed patients, and can prolong respiratory failure, lead to ventilator dependency, and contribute to the development of chronic critical illness. The etiology of NMDs are diverse and overlap, and distinguishing different disease entities by clinical exam and electrophysiologic studies can be difficult. CIP, which has been the most widely studied CINMA, represents the peripheral nervous system manifestation of the MODS. Patients with CIP, particularly those with severely reduced nerve function, have a prolonged rehabilitation and a high mortality rate. Although there are no definitive treatments, diagnosing a CINMA may provide helpful prognostic information. Future preventative measures may include immunoglobulin, nerve growth factors, or strict glycemic control, although in the CCI phase general supportive care is given, including prevention of iatrogenic complications, nutritional support, psychosocial support, and physical therapy. The early recognition of CINMAs and prevention of associated complications are important to enabling CCI patients with CINMAs to recover and return home with an acceptable functional level and quality of life.

What does beta-bungarotoxin do at the neuromuscular junction?

beta-Bungarotoxin from the Taiwan banded krait, Bungarus multicinctus is a basic protein (pI=9.5), with a molecular weight of 21,800 consisting of two different polypeptide subunits. A phospholipase A(2) subunit named the A-chain and a non-phospholipase A(2) subunit named the B-chain, which is homologous to Kunitz protease inhibitors. The A-chain and the B-chain are covalently linked by one disulphide bridge. On mouse hemi-diaphragm nerve-muscle preparations, partially paralysed by lowering the external Ca(2+) concentration, beta-bungarotoxin classically produces triphasic changes in the contraction responses to indirect nerve stimulation. The initial transient inhibition of twitches (phase 1) is followed by a prolonged facilitatory phase (phase 2) and finally a blocking phase (phase 3). These changes in twitch tension are mimicked, to some extent, by similar changes to end plate potential amplitude and miniature end plate potential frequency. The first and second phases are phospholipase-independent and are thought to be due to the B-chain (a dendrotoxin mimetic) binding to or near to voltage-dependent potassium channels. The last phase (phase 3) is phospholipase dependent and is probably due to phospholipase A(2)-mediated destruction of membrane phospholipids in motor nerve terminals.