Skeletal Muscle Metabolic Dysfunction in Patients With Malignant Hyperthermia Susceptibility

276th ENMC workshop: recommendations on optimal diagnostic pathway and management strategy for patients with acute rhabdomyolysis worldwide. 15th-17th March 2024, Hoofddorp, The Netherlands

The 276th ENMC Workshop on rhabdomyolysis brought together 21 experts to address the compelling need for standardized guidelines on the clinical approach of rhabdomyolysis. There was a general agreement that a diagnosis of rhabdomyolysis require that 1) clinical symptoms include severe muscle swelling, weakness and/or myalgia; 2) serum CK-levels exceed 10,000 IU/L in case of exertional, and >5000 IU/L in non-exertional rhabdomyolysis; 3) CK-levels reaching a maximum 1-4 days after the event and normalizing to baseline within 1-2 weeks of rest. In case of an underlying neuromuscular condition, CK-levels should exceed 5-10 times the patient's baseline level. Treatment should be initiated only in case of high risk on acute kidney injury, which can be predicted by the McMahon score. Furthermore, recommendations on performing genetic testing were formulated and the use of the 'RHABDO'- acronym was generally agreed upon as a tool to aid clinicians in deciding which patients require genetic testing. Moreover, recommendations on follow-up were made, with a particular emphasis on evaluation of physical and psychological sequelae. Patient representatives present during the workshop emphasized the importance of the current recommendations for future clinical guidelines on rhabdomyolysis.

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.

Epidemiological and clinical features of malignant hyperthermia: A scoping review

Malignant hyperthermia (MH) is a potentially fatal inherited pharmacogenetic disorder related to pathogenic variants in the RYR1, CACNA1S, or STAC3 genes. Early recognition of the occurrence of MH and prompt medical treatment are indispensable to ensure a positive outcome. The purpose of this study was to provide valuable information for the early identification of MH by summarizing epidemiological and clinical features of MH. This scoping review followed the methodological framework recommended by Arksey and O'Malley. PubMed, Embase, and Web of science databases were searched for studies that evaluated the epidemical and clinical characteristics of MH. A total of 37 studies were included in this review, of which 26 were related to epidemiology and 24 were associated with clinical characteristics. The morbidity of MH varied from 0.18 per 100 000 to 3.9 per 100 000. The mortality was within the range of 0%-18.2%. Identified risk factors included sex, age, disorders associated with MH, and others. The most frequent initial clinical signs included hyperthermia, sinus tachycardia, and hypercarbia. The occurrence of certain signs, such as hypercapnia, delayed first temperature measurement, and peak temperature were associated with poor outcomes. The epidemiological and clinical features of MH varied considerably and some risk factors and typical clinical signs were identified. The main limitation of this review is that the treatment and management strategies were not assessed sufficiently due to limited information.

Fatigue, depression, and physical activity in patients with malignant hyperthermia: a cross-sectional observational study

BACKGROUND

Malignant Hyperthermia (MH) is a pharmacogenetic disorder triggered by halogenated anesthesia agents/succinylcholine and characterized by hypermetabolism crisis during anesthesia, but also by day-to-day symptoms, such as exercise intolerance, that may alert the health professional.

OBJECTIVE

The study aimed to analyze the incidence of fatigue in MH susceptible patients and the variables that can impact perception of fatigue, such as the level of routine physical activity and depression.

METHODS

A cross-sectional observational study was carried out with three groups ... 22 patients susceptible to MH (positive in vitro muscle contracture test), 13 non-susceptible to MH (negative in vitro muscle contracture test) and 22 controls (no history of MH). Groups were assessed by a demographic/clinical questionnaire, a fatigue severity scale (intensity, specific situations, psychological consequences, rest/sleep response), and the Beck depression scale. Subgroups were re-assessed with the Baecke habitual physical exercise questionnaire (occupational physical activity, leisure physical exercise, leisure/locomotion physical activity).

RESULTS

There were no significant differences among the three groups regarding fatigue intensity, fatigue related to specific situations, psychological consequences of fatigue, fatigue response to resting/sleeping, depression, number of active/sedentary participants, and the mean time and characteristics of habitual physical activity. Nevertheless, unlike the control sub-group, the physically active MH-susceptible subgroup had a higher fatigue response to resting/sleeping than the sedentary MH susceptible subgroup (respectively, 5.9.ß...ß1.9 vs. 3.9.ß...ß2, t-test unpaired, p.ß<.ß0.05).

CONCLUSION

We did not detect subjective fatigue in MH susceptible patients, although we reported protracted recovery after physical activity, which may alert us to further investigation requirements.

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.

Sex-specific alterations in whole body energetics and voluntary activity in heterozygous R163C malignant hyperthermia-susceptible mice

Malignant hyperthermia (MH) is characterized by induction of skeletal muscle hyperthermia in response to a dysregulated increase in myoplasmic calcium. Although altered energetics play a central role in MH, MH‐susceptible humans and mouse models are often described as having no phenotype until exposure to a triggering agent. The purpose of this study was to determine the influence of the R163C ryanodine receptor 1 mutation, a common MH mutation in humans, on energy expenditure, and voluntary wheel running in mice. Energy expenditure was measured by indirect respiration calorimetry in wild‐type (WT) and heterozygous R163C (HET) mice over a range of ambient temperatures. Energy expenditure adjusted for body weight or lean mass was increased (P < .05) in male, but not female, HET mice housed at 22°C or when housed at 28°C with a running wheel. In female mice, voluntary wheel running was decreased (P < .05) in the HET vs WT animals when analyzed across ambient temperatures. The thermoneutral zone was also widened in both male and female HET mice. The results of the study show that the R163C mutations alters energetics even at temperatures that do not typically induce MH.

Skeletal Muscle Dysfunction and Exercise Intolerance in Children Treated with Haematopoietic Stem Cell Transplant-A Pilot Feasibility Study

Haematopoietic stem cell transplant (HSCT) is an intensive therapy for some pediatric hematological illnesses. Survivors are at risk for adverse effects including exercise intolerance. Peripheral tissue dysfunction may contribute to exercise intolerance; therefore, we examined the feasibility of a magnetic resonance spectroscopy (MRS) protocol to evaluate skeletal muscle metabolism in children post-HSCT. We measured demographic characteristics, aerobic exercise capacity (YMCA protocol), and skeletal muscle function in response to exercise (MRS; Siemens 3T MRI) in five children post-allogeneic HSCT and five age/body mass index-matched healthy controls (HCs). The mean age (± standard deviation) of the HSCT group and HC group were 11 ± 1.2 and 12.8 ± 2.4 years, respectively. Children post-HSCT had a lower peak aerobic exercise capacity compared to HCs (27.8 ± 3.4 vs. 40.3 ± 8.1 mL kg⁻¹ min⁻¹, respectively; p = 0.015). Exercise MRS testing protocols were successfully completed by all HSCT and HC participants; however, MRS-derived skeletal muscle metabolism variables were not different between the two groups. In conclusion, the use of exercise protocols in conjunction with MRS to assess peripheral skeletal muscle metabolism was achievable in children post-HSCT. In the future, larger studies should determine if skeletal muscle function is associated with exercise capacity in children post-HSCT.

Malignant hyperthermia: still an issue for neuromuscular diseases?

PURPOSE OF REVIEW

We will give an overview of neuromuscular disorders that can be linked with malignant hyperthermia or malignant hyperthermia-like reactions, and suggest an appropriate approach to interpret the risks.

RECENT FINDINGS

An increasing number of neuromuscular phenotypes have been linked to malignant hyperthermia susceptibility (MHS). This is for an important part due to the highly variable phenotype associated with mutations in the ryanodine receptor 1 gene (RYR1), the gene most frequently associated with MHS. A RYR1-mutation or a clinical RYR1-phenotype does not automatically translate in MHS, but precautions should be taken nonetheless. In addition, several other genes and phenotypes are now considered to be associated with MHS. In contrast, several neuromuscular diseases that were long thought to be linked to MHS are now known to cause malignant hyperthermia-like reactions instead of malignant hyperthermia. This is highly relevant as not only the given preoperative advice differs, but also acute treatment.

SUMMARY

This review provides a summary of current evidence linking certain neuromuscular diseases to malignant hyperthermia or malignant hyperthermia-like reactions. We provide a guide for the clinician, to determine which patients are at risk of malignant hyperthermia or malignant hyperthermia-like reactions perioperatively, and to ensure adequate treatment in case such a severe acute complication occurs.

Permeabilised skeletal muscle reveals mitochondrial deficiency in malignant hyperthermia-susceptible individuals

BACKGROUND

Individuals genetically susceptible to malignant hyperthermia (MH) exhibit hypermetabolic reactions when exposed to volatile anaesthetics. Mitochondrial dysfunction has previously been associated with the MH-susceptible (MHS) phenotype in animal models, but evidence of this in human MH is limited.

METHODS

We used high resolution respirometry to compare oxygen consumption rates (oxygen flux) between permeabilised human MHS and MH-negative (MHN) skeletal muscle fibres with or without prior exposure to halothane. A substrate-uncoupler-inhibitor titration protocol was used to measure the following components of the electron transport chain under conditions of oxidative phosphorylation (OXPHOS) or after uncoupling the electron transport system (ETS): complex I (CI), complex II (CII), CI+CII and, as a measure of mitochondrial mass, complex IV (CIV).

RESULTS

Baseline comparisons without halothane exposure showed significantly increased mitochondrial mass (CIV, P=0.021) but lower flux control ratios in CI+CII_(OXPHOS) and CII_(ETS) of MHS mitochondria compared with MHN (P=0.033 and 0.005, respectively) showing that human MHS mitochondria have a functional deficiency. Exposure to halothane triggered a hypermetabolic response in MHS mitochondria, significantly increasing mass-specific oxygen flux in CI_(OXPHOS), CI+CII_(OXPHOS), CI+CII_(ETS), and CII_(ETS) (P=0.001-0.012), while the rates in MHN samples were unaltered by halothane exposure.

CONCLUSIONS

We present evidence of mitochondrial dysfunction in human MHS skeletal muscle both at baseline and after halothane exposure.