Exertional Heat Stroke and Susceptibility to Malignant Hyperthermia in an Athlete: Evidence for a Link?

Heatstroke-Induced Inflammatory Response and Therapeutic Biomarkers

In recent years, heatstroke has become one of the most dangerous illnesses associated with hyperthermia. Hyperthermia is described as an increased body temperature, where there is more heat accrual than dissipation, which happens during environmental heat stress conditions or exhaustive exercise and subsequently leads to heatstroke. Heatstroke is characterized as a dysfunction of the central nervous system (CNS), associated with neuroinflammation, including utmost hyperthermia, which eventually leads to multiorgan failure. Heatstroke-related fatalities have rapidly increased in the recent past; however, there is still a gap in the understanding of heatstroke and associated outcomes during heatstroke. Especially of note, early diagnosis of heatstroke-related complications is one of the important aspects that need to be addressed. This article reviewed current knowledge about heatstroke and associated inflammatory responses, including neuroinflammation and other clinical complications. Using molecular dynamics simulation analysis of triose phosphate isomerase (a housekeeping enzyme) at different temperatures, we demonstrated how protein structures, and thus their functions, can be varied with temperature increases. Additionally, we discussed therapeutically relevant biomarkers of heatstroke which might be helpful in the early detection of heatstroke possibilities and candidate drug targets to control or minimize heatstroke events.

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.

Heat stroke: Pathogenesis, diagnosis, and current treatment

Recently, the incidence of heat-related illnesses has exhibited a steadily upward trend, which is closely associated with several environmental factors such as climate change and air pollution. The progression of heat-related illnesses is a continuous process and can progress to the terminal period when it transforms into heat stroke, the most severe form. Heat stroke is markedly by a core body temperature above 40°C and central nervous system dysfunction. Current knowledge suggests that the pathogenesis of heat stroke is complex and varied, including inflammatory response, oxidative stress, cell death, and coagulation dysfunction. This review consolidated recent research progress on the pathophysiology and pathogenesis of heat stroke, with a focus on the related molecular mechanisms. In addition, we reviewed common strategies and sorted out the drugs in various preclinical stages for heat stroke, aiming to offer a comprehensive research roadmap for more in-depth researches into the mechanisms of heat stroke and the reduction in the mortality of heat stroke in the future.

Heat-hypersensitive mutants of ryanodine receptor type 1 revealed by microscopic heating

Malignant hyperthermia (MH) is a life-threatening disorder caused largely by mutations in ryanodine receptor type 1 (RyR1) Ca²⁺-release channels. Enhanced Ca²⁺ release through the mutant channels induces excessive heat development upon exposure to volatile anesthetics. However, the mechanism by which Ca²⁺ release is accelerated at an elevated temperature is yet to be identified. Fluorescence Ca²⁺ imaging with rapid heating by an infrared laser beam provides direct evidence that heat induces Ca²⁺ release through the RyR1 channel. And the mutant channels are more heat sensitive than the wild-type channels, thereby causing an increase in the cytosolic Ca²⁺ concentration in mutant cells. It is likely that the heat-induced Ca²⁺ release participates as an enhancer in the cellular mechanism of MH.

Thermoregulation is an important aspect of human homeostasis, and high temperatures pose serious stresses for the body. Malignant hyperthermia (MH) is a life-threatening disorder in which body temperature can rise to a lethal level. Here we employ an optically controlled local heat-pulse method to manipulate the temperature in cells with a precision of less than 1 °C and find that the mutants of ryanodine receptor type 1 (RyR1), a key Ca²⁺ release channel underlying MH, are heat hypersensitive compared with the wild type (WT). We show that the local heat pulses induce an intracellular Ca²⁺ burst in human embryonic kidney 293 cells overexpressing WT RyR1 and some RyR1 mutants related to MH. Fluorescence Ca²⁺ imaging using the endoplasmic reticulum–targeted fluorescent probes demonstrates that the Ca²⁺ burst originates from heat-induced Ca²⁺ release (HICR) through RyR1-mutant channels because of the channels’ heat hypersensitivity. Furthermore, the variation in the heat hypersensitivity of four RyR1 mutants highlights the complexity of MH. HICR likewise occurs in skeletal muscles of MH model mice. We propose that HICR contributes an additional positive feedback to accelerate thermogenesis in patients with MH.

RYR1-related rhabdomyolysis: a spectrum of hypermetabolic states due to ryanodine receptor dysfunction

Variants in the ryanodine receptor-1 gene (RYR1) have been associated with a wide range of neuromuscular conditions, including various congenital myopathies and malignant hyperthermia (MH). More recently, a number of RYR1 variants, mostly MH-associated, have been demonstrated to contribute to rhabdomyolysis events not directly related to anesthesia in otherwise healthy individuals. This review focuses on RYR1-related rhabdomyolysis, in the context of several clinical presentations (i.e., exertional rhabdomyolysis, exertional heat illnesses and MH), and conditions involving a similar hypermetabolic state, in which RYR1 variants may be present (i.e., neuroleptic malignant syndrome and serotonin syndrome). The variety of triggers that can evoke rhabdomyolysis, on their own or in combination, as well as the number of potentially associated complications, illustrates that this is a condition relevant to several medical disciplines. External triggers include but are not limited to strenuous physical exercise, especially if unaccustomed or performed under challenging environmental conditions (e.g., high ambient temperature or humidity), alcohol/illicit drugs, prescription medication (in particular statins, other anti-lipid agents, antipsychotics and antidepressants) infection, or heat. Amongst all patients presenting with rhabdomyolysis, a genetic susceptibility is present in a proportion, with RYR1 being one of the most common genetic causes. Clinical clues for a genetic susceptibility include recurrent rhabdomyolysis, creatine kinase (CK) levels above 50 times the upper limit of normal, hyperCKemia lasting for 8 weeks or longer, drug/medication doses insufficient to explain the rhabdomyolysis event, and a positive family history. For the treatment or prevention of RYR1-related rhabdomyolysis, the RYR1 antagonist dantrolene can be administered, both in the acute phase, or prophylactically in patients with a history of muscle cramps and/or recurrent rhabdomyolysis events. Aside from dantrolene, several other drugs are being investigated for their potential therapeutic use in RYR1-related disorders. These findings offer further therapeutic perspectives for humans, suggesting an important area for future research.

Fatal postoperative malignant hyperthermia following rhinoplasty in a patient with one variant of the ryanodine receptor 1 (RYR1) gene

Malignant hyperthermia (MH) is characterized by a rapid rise in body temperature after using inhalational anesthetics and depolarizing muscle relaxants. A 19-year-old female had a rapidly developing fever up to 43.0 °C, after rhinoplasty surgery. Inhalational anesthetics and depolarizing muscle relaxants were used in general anesthesia. It was suspected that the patient died of MH. The medico-legal autopsy findings showed classical MH histopathological changes in the skeletal muscles, cardiac muscles, as well as lungs. Additionally, postmortem blood biochemical results indicated rhabdomyolysis. A combination of clinical records and autopsy revealed that MH might have caused the death. A diagnostic genetic testing was performed to confirm the existence of MH, and an MH diagnostic variant RYR1 c.7048G >A (p. A2350T) was detected. Eventually, the cause of death was determined as MH based on clinical records, autopsy, and genetic analysis. This case highlights that diagnostic genetic analysis plays a vital role in postmortem diagnosis of MH in routine medico-legal contexts.

Impact of rhabdomyolysis on outcomes of hospitalizations for heat stroke in the United States

BACKGROUND

The objective of this study was to evaluate the predictors and associated outcomes of rhabdomyolysis in admitted patients for heat stroke in the United States.

METHODS

The National Inpatient Sample was utilized to identify hospitalized patients with a primary diagnosis of heat stroke from the years 2003-2014. Rhabdomyolysis was identified using hospital diagnosis code. We compared the clinical characteristics, in-hospital treatment, complications, outcomes, and resource utilization between patients with and without rhabdomyolysis.

RESULTS

A total of 3,372 hospital admissions for heat stroke were studied. Of these, rhabdomyolysis occurred in 1049 (31%) admissions. The risk factors for rhabdomyolysis were age 20-39 years, male sex, African American race, history of alcohol drinking, whereas age ≥60 years, smoking, history of diabetes mellitus, and hypertension were associated with lower risk of rhabdomyolysis. Patients with rhabdomyolysis had greater requirements for mechanical ventilation, blood component transfusion, and renal replacement therapy. Rhabdomyolysis was significantly associated with increased risk of hyponatremia, hypernatremia, hyperkalemia, hypocalcemia, serum phosphorus and magnesium derangement, metabolic acidosis, sepsis, ventricular arrhythmia or cardiac arrest, renal failure, respiratory failure, liver failure, neurological failure, hematologic failure, and in-hospital mortality. Length of hospital stay and hospitalization cost were higher when rhabdomyolysis occurred during hospital stay.

CONCLUSION

Rhabdomyolysis occurred in about one-third of hospitalized patients for heat stroke and was associated with increased morbidity, mortality, and resource utilization.

Physical exercise and seizure activity

Neuroprotective and antiepileptogenic therapies have been extensively investigated for epilepsy prevention and treatment. This review gives an overview of the promising contribution of the ketogenic diet, a complementary treatment, on the intestinal microbiota to reduce seizure susceptibility. Next, the relevance of physical exercise is extensively addressed as a complementary therapy to reduce seizure susceptibility, and thereby impact beneficially on the epilepsy condition. In this context, particular attention is given to the potential risks and benefits of physical exercise, possible precipitant factors related to exercise and proposed mechanisms by which exercise can reduce seizures, and its antiepileptogenic effects. Finally, this review points to emerging evidence of exercise reducing comorbidities from epilepsy and improving the quality of life of people with epilepsy. Based on evidence from current literature, physical or sport activities represent a potential non-pharmacological intervention that can be integrated with conventional therapy for epilepsy.

Individual risk factors associated with exertional heat illness: A systematic review

NEW FINDINGS

What is the topic of this review? Exertional heat illness (EHI) remains a persistent problem for athletes and individuals. This threat remains despite numerous athletic position statements and occupational guidance policies. This review explores primary evidence that demonstrates a direct association between 'known' risk factors and EHI. What advances does it highlight? Primary evidence to support 'known' risk factors associated with EHI is not comprehensive. Furthermore, it is not evident that single individual factors predispose individuals to greater risk. In fact, the evidence indicates that EHI can manifest in non-hostile compensable environments when a combination of risk factors is prevalent.

ABSTRACT

Despite the widespread knowledge of exertional heat illness (EHI) and clear guidance for its prevention, the incidence of EHI remains high. We carried out a systematic review of available literature evaluating the scientific evidence underpinning the risk factors associated with EHI. Medline, PsycINFO, SportDiscus and Embase were searched from inception to January 2019 with no date limitation, with supplementary searches also being performed. Search terms included permutations of risk and heat illness, with only studies in English included. Study selection, data extraction and quality assessment, using the QUALSYST tool, were performed by two independent reviewers. Of 8898 articles identified by the searches, 42 were included in the systematic review as primary evidence demonstrating a link between a risk factor and EHI. The quality scores ranged from 57.50 to 100%, and studies were generally considered to be of strong quality. The majority of risks attributable to EHI were categorized as those associated with lifestyle factors. The findings from the systematic review suggest complex manifestation of EHI through multiple risk factors rather than any one factor in isolation. Further research is needed to explore the accumulation of risk factors to help in development of effective preventative measures.

The current status of malignant hyperthermia

Malignant hyperthermia (MH) is a rare and life-threatening pharmacogenetic disorder triggered by volatile anesthetics, the depolarizing muscle relaxant succinylcholine, and rarely by strenuous exercise or environmental heat. The exact prevalence of MH is unknown, and it varies from 1:16 000 in Denmark to 1:100 000 in New York State. The underlying mechanism of MH is excessive calcium release from the sarcoplasmic reticulum (SR), leading to uncontrolled skeletal muscle hyper-metabolism. Genetic mutations in ryanodine receptor type 1 ( RYR1) and CACNA1S have been identified in approximately 50% to 86% and 1% of MH-susceptible (MHS) individuals, respectively. Classic clinical symptoms of MH include hypercarbia, sinus tachycardia, masseter spasm, hyperthermia, acidosis, muscle rigidity, hyperkalemia, myoglobinuria, and etc. There are two types of testing for MH: a genetic test and a contracture test. Contracture testing is still being considered as the gold standard for MH diagnosis. Dantrolene is the only available drug approved for the treatment of MH through suppressing the calcium release from SR. Since clinical symptoms of MH are highly variable, it can be difficult to establish a diagnosis of MH. Nevertheless, prompt diagnosis and treatments are crucial to avoid a fatal outcome. Therefore, it is very important for anesthesiologists to raise awareness and understand the characteristics of MH. This review summarizes epidemiology, clinical symptoms, diagnosis and treatments of MH and any new developments.

Malignant Hyperthermia Susceptibility and Related Diseases

This review identifies disease states associated with malignant hyperthermia susceptibility based on genotypic and phenotypic findings, and a framework is established for clinicians to identify a potentially malignant hyperthermia–susceptible patient.

RYR1-related rhabdomyolysis: A common but probably underdiagnosed manifestation of skeletal muscle ryanodine receptor dysfunction

Mutations in the skeletal muscle ryanodine receptor (RYR1) gene are associated with a wide spectrum of inherited myopathies presenting throughout life. Malignant hyperthermia susceptibility (MHS)-related RYR1 mutations have emerged as a common cause of exertional rhabdomyolysis, accounting for up to 30% of rhabdomyolysis episodes in otherwise healthy individuals. Common triggers are exercise and heat and, less frequently, viral infections, alcohol and drugs. Most subjects are normally strong and have no personal or family history of malignant hyperthermia. Heat intolerance and cold-induced muscle stiffness may be a feature. Recognition of this (probably not uncommon) rhabdomyolysis cause is vital for effective counselling, to identify potentially malignant hyperthermia-susceptible individuals and to adapt training regimes. Studies in various animal models provide insights regarding possible pathophysiological mechanisms and offer therapeutic perspectives.