Myopathic manifestations across the adult lifespan of patients with malignant hyperthermia susceptibility: a narrative review.

Malignant hyperthermia susceptibility (MHS) designates individuals at risk of developing a hypermetabolic reaction triggered by halogenated anaesthetics or the depolarising neuromuscular blocking agent suxamethonium. Over the past few decades, beyond the operating theatre, myopathic manifestations impacting daily life are increasingly recognised as a prevalent phenomenon in MHS patients. At the request of the European Malignant Hyperthermia Group, we reviewed the literature and gathered the opinion of experts to define MHS-related myopathy as a distinct phenotype expressed across the adult lifespan of MHS patients unrelated to anaesthetic exposure; this serves to raise awareness about non-anaesthetic manifestations, potential therapies, and management of MHS-related myopathy. We focused on the clinical presentation, biochemical and histopathological findings, and the impact on patient well-being. The spectrum of symptoms of MHS-related myopathy encompasses muscle cramps, stiffness, myalgias, rhabdomyolysis, and weakness, with a wide age range of onset mainly during adulthood. Histopathological analysis can reveal nonspecific abnormalities suggestive of RYR1 involvement, while metabolic profiling reflects altered energy metabolism in MHS muscle. Myopathic manifestations can significantly impact patient quality of life and lead to functional limitations and socio-economic burden. While currently available therapies can provide symptomatic relief, there is a need for further research into targeted treatments addressing the underlying pathophysiology. Counselling early after establishing the MHS diagnosis, followed by multidisciplinary management involving various medical specialties, is crucial to optimise patient care.

Malignant Hyperthermia.

OBJECTIVES: A narrative expert review aiming to summarize the clinical epidemiology and management of critically ill patients with malignant hyperthermia (MH). DATA SOURCES: Medline searches were conducted to identify relevant articles describing the epidemiology, pathophysiology, and management of MH. Guidelines from key MH organizations were also incorporated into this review. STUDY SELECTION: Relevant studies regarding MH in both ICU and perioperative settings were reviewed. DATA EXTRACTION: Data from relevant studies were summarized and qualitatively assessed. DATA SYNTHESIS: MH is a severe reaction triggered by inhalational volatile anesthetics and succinylcholine in genetically susceptible patients. The condition is characterized by an early onset (min to hr) rise in temperature, hypercarbia, and muscular rigidity following exposure to triggering medications with potential complications of coagulopathy, rhabdomyolysis, and acute kidney injury. Acute management necessitates a coordinated multidisciplinary team approach with specific management using dantrolene, active cooling, and hyperventilation. A suspected MH reaction has important implications for future anesthetic exposure for both the patient and their family. All suspected reactions should be followed up at a specialized MH testing center using muscle contracture and genetic testing. CONCLUSIONS: Increasing use of inhalational anesthetics in the ICU underscores the need for enhanced education on the diagnosis and management of MH to ensure optimal patient sedation care and safety.

Uncoupling cytosolic calcium from membrane voltage by transient receptor potential melastatin 4 channel (TRPM4) modulation: A novel strategy to treat ventricular arrhythmias.

The current antiarrhythmic paradigm is mainly centered around modulating membrane voltage. However, abnormal cytosolic calcium (Ca2+) signaling, which plays an important role in driving membrane voltage, has not been targeted for therapeutic purposes in arrhythmogenesis. There is clear evidence for bidirectional coupling between membrane voltage and intracellular Ca2+. Cytosolic Ca2+ regulates membrane voltage through Ca2+-sensitive membrane currents. As a component of Ca2+-sensitive currents, Ca2+-activated nonspecific cationic current through the TRPM4 (transient receptor potential melastatin 4) channel plays a significant role in Ca2+-driven changes in membrane electrophysiology. In myopathic and ischemic ventricles, upregulation and/or enhanced activity of this current is associated with the generation of afterdepolarization (both early and delayed), reduction of repolarization reserve, and increased propensity to ventricular arrhythmias. In this review, we describe a novel concept for the management of ventricular arrhythmias in the remodeled ventricle based on mechanistic concepts from experimental studies, by uncoupling the Ca2+-induced changes in membrane voltage by inhibition of this TRPM4-mediated current.

Optimizing neuromuscular blockade management for improving patient safety and peri-operative outcomes: a pilot phase of a quality improvement initiative.

INTRODUCTION: Although quantitative monitoring of neuromuscular blockade (NMB) is recommended, it is not routinely used in daily practice. The optimizing NMB management to improve patient safety and perioperative outcomes (OBISPO) quality improvement (QI) initiative intends to address this issue and change clinicians' behaviors. MATERIAL AND METHODS: A pilot phase of the prospective QI intervention was conducted. The primary objective was implement clinical practice change that emphasizes improving NMB monitoring in patients undergoing elective cardiac surgery who are eligible for fast-track extubation between February 2021 and December 2021. The secondary objective was to reduce the train-of-four ratio (TOFR) < 0.9 incidence before tracheal extubation to less than 20%. The intervention included educational sessions for teams. RESULTS: A total of 859 patients underwent elective cardiac surgery, 40% were eligible for fast-track extubation. From our cohort of fast-track cardiac cases, 69% had reported TOFR; 47% of them had residual paralysis (TOFR < 0.9) on arrival to PACU, 22% persisted with residual paralysis after extubation, and 27% were extubated without monitoring. The survey identified cognitive biases, knowledge gaps, unfamiliarity, and lack of trust in quantitative monitoring devices. Workflow disruptions imposed by COVID and changes in NMB monitoring devices have negatively affected our initiative. CONCLUSIONS: Our study showed that changes in clinician behavior are among the most challenging issues in perioperative medicine. Continuous teaching and QI initiatives, focused on quantitative NMB monitors and adequate reversal agent use, are mandatory to improve perioperative outcomes. Therefore, new proposals are required to promote changes in current practices.

Distinct pathophysiological characteristics in developing muscle from patients susceptible to malignant hyperthermia.

BACKGROUND: Most patients with malignant hyperthermia susceptibility diagnosed by the in vitro caffeine-halothane contracture test (CHCT) develop excessive force in response to halothane but not caffeine (halothane-hypersensitive). Hallmarks of halothane-hypersensitive patients include high incidence of musculoskeletal symptoms at rest and abnormal calcium events in muscle. By measuring sensitivity to halothane of myotubes and extending clinical observations and cell-level studies to a large group of patients, we reach new insights into the pathological mechanism of malignant hyperthermia susceptibility. METHODS: Patients with malignant hyperthermia susceptibility were classified into subgroups HH and HS (positive to halothane only and positive to both caffeine and halothane). The effects on [Ca2+]cyto of halothane concentrations between 0.5 and 3 % were measured in myotubes and compared with CHCT responses of muscle. A clinical index that summarises patient symptoms was determined for 67 patients, together with a calcium index summarising resting [Ca2+]cyto and spontaneous and electrically evoked Ca2+ events in their primary myotubes. RESULTS: Halothane-hypersensitive myotubes showed a higher response to halothane 0.5% than the caffeine-halothane hypersensitive myotubes (P<0.001), but a lower response to higher concentrations, comparable with that used in the CHCT (P=0.055). The HH group had a higher calcium index (P<0.001), but their clinical index was not significantly elevated vs the HS. Principal component analysis identified electrically evoked Ca2+ spikes and resting [Ca2+]cyto as the strongest variables for separation of subgroups. CONCLUSIONS: Enhanced sensitivity to depolarisation and to halothane appear to be the primary, mutually reinforcing and phenotype-defining defects of halothane-hypersensitive patients with malignant hyperthermia susceptibility.

Oral Dantrolene for Myopathic Symptoms in Malignant Hyperthermia-Susceptible Patients: A 25-Year Retrospective Cohort Study of Adverse Effects and Tolerability.

BACKGROUND: Patients susceptible to malignant hyperthermia (MH) may experience disabling manifestations of an unspecified myopathy outside the context of anesthesia, including myalgia, fatigue, or episodic rhabdomyolysis. Clinical observations suggest that oral dantrolene may relief myopathic symptoms in MH-susceptible (MHS) patients. However, high-dose oral dantrolene has been associated with severe hepatotoxicity. METHODS: In a retrospective database review (1994-2018), we investigated a cohort of patients who were diagnosed as MHS by a positive caffeine-halothane contracture test (CHCT), had myopathic manifestations, and received oral dantrolene. Our aim was to investigate the occurrence of serious adverse effects and the adherence to oral dantrolene therapy. We also explored factors associated with self-reported clinical improvement, considering as nonresponders patients with intolerable adverse effects or who reported no improvement 8 weeks after starting treatment. RESULTS: Among 476 MHS patients with positive CHCT, 193 had muscle symptoms, 164 started oral dantrolene, 27 refused treatment, and 2 were excluded due to abnormal liver function before starting therapy. There were no serious adverse effects reported. Forty-six of 164 patients (28%; 95% confidence interval [CI], 22%-35%) experienced mild to moderate adverse effects. Twenty-two patients (22/164, 13%; 95% CI, 9%-19%) discontinued treatment, among which 16 due to adverse effects and 6 due to lack of improvement. One hundred forty-two patients (87%; 95% CI, 80%-90%) adhered to therapy and reported improvement of myalgia (n = 78), fatigue (n = 32), or rhabdomyolysis/hiperCKemia (n = 32). The proportion of responders was larger among patients with MH history than among those referred due to a clinical myopathy with nonpertinent anesthetic history (97% vs 79%, respectively; 95% CI of the difference, 8.5-28; P < .001). Patients with a sarcoplasmic reticulum Ca2+ release channel ryanodine receptor gene ( RYR1 ) variant had higher odds of responding to dantrolene treatment (OR, 6.4; 95% CI, 1.3-30.9; P = .013). Dantrolene median dose was 50 (25-400) and 200 (25-400) mg·day -1 in responders and nonresponders, respectively. CONCLUSIONS: We found that oral dantrolene produced no serious adverse effects within the reported dose range, and was well tolerated by most MH-susceptible patients presenting myopathic symptoms. Our study provides dosing and adverse effect data as a basis for further randomized controlled clinical trials to determine the efficacy of oral dantrolene for symptomatic relief in MHS-related myopathies.

Untargeted metabolomics profiling of skeletal muscle samples from malignant hyperthermia susceptible patients.

PURPOSE: Malignant hyperthermia (MH) is a potentially fatal hypermetabolic condition triggered by certain anesthetics and caused by defective calcium homeostasis in skeletal muscle cells. Recent evidence has revealed impairment of various biochemical pathways in MH-susceptible patients in the absence of anesthetics. We hypothesized that clinical differences between MH-susceptible and control individuals are reflected in measurable differences in myoplasmic metabolites. METHODS: We performed metabolomic profiling of skeletal muscle samples from MH-negative (control) individuals and MH-susceptible patients undergoing muscle biopsy for diagnosis of MH susceptibility. Cellular metabolites were extracted from 33 fresh and 87 frozen human muscle samples using solid phase microextraction and Metabolon® untargeted biochemical profiling platforms, respectively. Ultra-performance liquid chromatography-high resolution mass spectrometry was used for metabolite identification and validation, followed by analysis of differences in metabolites between the MH-susceptible and MH-negative groups. RESULTS: Significant fold-change differences between the MH-susceptible and control groups in metabolites from various pathways were found (P value range: 0.009 to < 0.001). These included accumulation of long chain acylcarnitines, diacylglycerols, phosphoenolpyruvate, histidine pathway metabolites, lysophosphatidylcholine, oxidative stress markers, and phosphoinositols, as well as decreased levels of monoacylglycerols. The results from both analytical platforms were in agreement. CONCLUSION: This metabolomics study indicates a shift from utilization of carbohydrates towards lipids for energy production in MH-susceptible individuals. This shift may result in inefficiency of beta-oxidation, and increased muscle protein turnover, oxidative stress, and/or lysophosphatidylcholine levels.

RéSUMé: OBJECTIF : L'hyperthermie maligne (HM) est une condition hypermétabolique potentiellement mortelle déclenchée par certains agents anesthésiques et causée par une homéostasie calcique perturbée des cellules musculaires squelettiques. Des données probantes récentes ont mis en lumière une atteinte de diverses voies biochimiques chez les patients susceptibles à l'HM en l'absence d'anesthésiques. Nous avons émis l'hypothèse que les différences cliniques entre les individus susceptibles à l'HM et des témoins se refléteraient dans des différences mesurables de métabolites myoplasmiques. MéTHODE : Nous avons réalisé un profilage métabolomique d'échantillons de muscles squelettiques provenant de personnes négatives à l'HM (témoins) et de patients susceptibles à l'HM subissant une biopsie musculaire dans le but de poser un diagnostic de susceptibilité à l'HM. Les métabolites cellulaires ont été extraits de 33 échantillons de muscles humains frais et de 87 échantillons congelés à l'aide d'une microextraction en phase solide et des plateformes de profilage biochimique non ciblées Metabolon®, respectivement. La chromatographie en phase liquide à haute performance et la spectrométrie de masse à haute résolution ont été utilisées pour l'identification et la validation des métabolites, puis suivies d'une analyse des différences dans les métabolites entre les groupes susceptibles à l'HM et les groupes négatifs à l'HM. RéSULTATS : Des différences significatives ont été observées entre les groupes susceptibles à l'HM et les groupes témoins dans les métabolites issus de diverses voies (P : de 0,009 à < 0,001). Ces différences comprenaient l'accumulation d'acylcarnitines à longue chaîne, de diacylglycérols, de phosphoénolpyruvate, de métabolites de la voie d'histidine, de lysophosphatidylcholine, de marqueurs de stress oxydatif, et de phosphoinositols, aussi bien que des taux réduits de monoacylglycérols. Les résultats des deux plateformes analytiques concordaient. CONCLUSION : Cette étude métabolomique indique un changement de l'utilisation des glucides vers les lipides pour la production d'énergie chez les personnes susceptibles à l'HM. Ce changement pourrait entraîner une inefficacité de la bêta-oxydation, ainsi qu'une augmentation du renouvellement des protéines musculaires, du stress oxydatif, et/ou des taux de lysophosphatidylcholine.

A multi-dimensional analysis of genotype-phenotype discordance in malignant hyperthermia susceptibility.

BACKGROUND: Malignant hyperthermia (MH) susceptibility is an inherited condition, diagnosed either by the presence of a pathogenic genetic variant or by in vitro caffeine-halothane contracture testing. Through a multi-dimensional approach, we describe the implications of discordance between genetic and in vitro test results in a patient with a family history of possible MH. METHODS: The patient, whose brother had a possible MH reaction, underwent the caffeine-halothane contracture test (CHCT) according to the North American MH Group protocol. Screening of the complete RYR1 and CACNA1S transcripts was done using Sanger sequencing. Additional functional analyses included skinned myofibre calcium-induced calcium release sensitivity, calcium signalling assays in cultured myotubes, and in silico evaluation of the effect of any genetic variants on their chemical environment. RESULTS: The patient's CHCT result was negative but she carried an RYR1 variant c.1209C>G, p.Ile403Met, that is listed as pathogenic by the European Malignant Hyperthermia Group. Functional tests indicated a gain-of-function effect with a weak impact, and the variant was predicted to affect the folding stability of the 3D structure of the RyR1 protein. Based on American College of Medical Genetics and Genomics/Association of Molecular Pathology guidelines, this variant would be characterised as a variant of uncertain significance. CONCLUSIONS: Available data do not confirm or exclude an increased risk of MH for this patient. Further research is needed to correlate RyR1 functional assays, including the current gold standard testing for MH susceptibility, with clinical phenotypes. The pathogenicity of genetic variants associated with MH susceptibility should be re-evaluated.

An Assessment of Penetrance and Clinical Expression of Malignant Hyperthermia in Individuals Carrying Diagnostic Ryanodine Receptor 1 Gene Mutations.

BACKGROUND: Malignant hyperthermia (MH) is a potentially lethal disorder triggered by certain anesthetics. Mutations in the ryanodine receptor 1 (RYR1) gene account for about half of MH cases. Discordance between the low incidence of MH and a high prevalence of mutations has been attributed to incomplete penetrance, which has not been quantified yet. The authors aimed to examine penetrance of MH-diagnostic RYR1 mutations and the likelihood of mutation carriers to develop MH, and to identify factors affecting severity of MH clinical expression. METHODS: In this multicenter case-control study, data from 125 MH pedigrees between 1994 and 2017 were collected from four European registries and one Canadian registry. Probands (survivors of MH reaction) and their relatives with at least one exposure to anesthetic triggers, carrying one diagnostic RYR1 mutation, were included. Penetrance (percentage of probands among all genotype-positive) and the probability of a mutation carrier to develop MH were obtained. MH onset time and Clinical Grading Scale score were used to assess MH reaction severity. RESULTS: The overall penetrance of nine RYR1 diagnostic mutations was 40.6% (93 of 229), without statistical differences among mutations. Likelihood to develop MH on exposure to triggers was 0.25 among all RYR1 mutation carriers, and 0.76 in probands (95% CI of the difference 0.41 to 0.59). Penetrance in males was significantly higher than in females (50% [62 of 124] vs. 29.7% [30 of 101]; P = 0.002). Males had increased odds of developing MH (odds ratio, 2.37; 95% CI, 1.36 to 4.12) despite similar levels of exposure to trigger anesthetics. Proband's median age was 12 yr (interquartile range 6 to 32.5). CONCLUSIONS: Nine MH-diagnostic RYR1 mutations have sex-dependent incomplete penetrance, whereas MH clinical expression is influenced by patient's age and the type of anesthetic. Our quantitative evaluation of MH penetrance reinforces the notion that a previous uneventful anesthetic does not preclude the possibility of developing MH.