Pre-operative exercise and pyrexia as modifying factors in malignant hyperthermia (MH)

Malignant hyperthermia (MH) is a life-threatening reaction triggered by volatile anesthetics and succinylcholine. MH is caused by mutations in the skeletal muscle ryanodine receptor (RYR1) gene, as is rhabdomyolysis triggered by exertion and/or pyrexia. The discrepancy between the prevalence of risk genotypes and actual MH incidence remains unexplained. We investigated the role of pre-operative exercise and pyrexia as potential MH modifying factors. We included cases from 5 MH referral centers with 1) clinical features suggestive of MH, 2) confirmation of MH susceptibility on Contracture Testing (IVCT or CHCT) and/or RYR1 genetic testing, and a history of 3) strenuous exercise within 72 h and/or pyrexia >37.5 °C prior to the triggering anesthetic. Characteristics of MH-triggering agents, surgery and succinylcholine use were collected. We identified 41 cases with general anesthesias resulting in an MH event (GA+MH, n = 41) within 72 h of strenuous exercise and/or pyrexia. We also identified previous general anesthesias without MH events (GA-MH, n = 51) in the index cases and their MH susceptible relatives. Apart from pre-operative exercise and/or pyrexia, trauma and acute abdomen as surgery indications, emergency surgery and succinylcholine use were also more common with GA+MH events. These observations suggest a link between pre-operative exercise, pyrexia and MH.

Cardiac anomalies associated with Escobar syndrome: A case report and a review of the literature

RATIONALE

Escobar syndrome (ES) is an autosomal recessive disorder. It is highly characterized by facial abnormalities, congenital diaphragmatic muscle weakness, myasthenic-like features, and skin pterygiums on multiple body legions. ES is a rare condition associated with many external and internal abnormalities. The internal malformations described in ES affect many organs including the heart, lungs, esophagus, liver, spleen, and intestine. The purpose of this paper is to explore the cardiac manifestations associated with ES.

PATIENT CONCERNS

A 3.5-year-old girl, who was born for double first cousins, was admitted to the hospital for neuromuscular evaluation of multiple congenital contractures.

DIAGNOSIS

The girl was diagnosed with ES and isolated dextrocardia which is a rare cardiac manifestation. However, to the best of our knowledge, no similar cases have been reported to date, and this case is thus believed to be very rare.

INTERVENTIONS

The patient underwent an operative intervention to correct the bilateral fixed flexion deformity at her knees which was related to the posterior bilateral fibrotic bands/pterygia.

OUTCOMES

Post-operatively, complete knee extension was obtained, the patient was fitted with a cast and extension night splint. She was discharged alive and had no complications. The patient was followed regularly in the orthopedic clinic and had periodic physiotherapy sessions.

CONCLUSIONS

ES and isolated dextrocardia concurrence in the presented case resulted from different pathogenic mechanisms. Our findings suggest that ES might be caused by dysfunction in the acetylcholine receptor throughout fetal life, which may have affected muscle strength and movement. Other cardiac conditions include hypoplastic left-sided heart, Hypertrophic cardiomyopathy, patent ductus arteriosus, and heterotaxia.

Malignant Hyperthermia Update

Malignant hyperthermia (MH) is a rare but potentially lethal skeletal muscle disorder affecting calcium release channels. It is inherited in a mendelian autosomal dominant pattern with variable penetration. The initial clinical manifestations are of a hypermetabolic state with increased CO2 production, respiratory acidosis, increased temperature, and increased oxygen demands. If diagnosed late, MH progresses to multi-organ system failure and death. Current data suggest that mortality has improved to less than 5%. The gold standard for ruling out MH is the contracture test. Genetic testing is also available. MH-susceptible individuals should be clearly identified for safe administration of future anesthetics.

Fatal awake malignant hyperthermia episodes in a family with malignant hyperthermia susceptibility: a case series

PURPOSE

The present report of two fatal awake malignant hyperthermia (MH) episodes in an MH susceptible (MHS) family is intended to raise awareness among medical personnel and MHS individuals to the possibility of life-threatening non-anesthesia-triggered MH episodes and to provide a strong incentive for development of effective preventive measures.

CLINICAL FEATURES

Two young athletic males (28 and 16 yr old), members of the same extended family with a history of anesthesia-related MH episodes and deaths, succumbed ten years apart on two different continents, with symptoms unrelated to anesthesia but strikingly similar to typical anesthetic-induced MH. Both suffered an abrupt surge in body temperature, tachycardia, tachypnea, muscle rigidity, hyperkalemia, and respiratory and metabolic acidosis. Despite aggressive resuscitation attempts, both developed cardiac arrest and died shortly upon arrival to hospital emergency departments. Autopsy analyses were negative for drugs, alcohol, or bacterial infection. Individual and familial genetic analyses revealed a novel, potentially pathogenic RYR1 variant (p.Gly159Arg) that co-segregates with the MHS phenotype in the family. Both fatal awake MH episodes are hypothesized to have been triggered by physical exertion compounded with a febrile illness that in one case was due to influenza type A.

CONCLUSIONS

Life-threatening awake MH episodes may develop in some MHS individuals in the absence of anesthetic triggers. Potential triggers can be physical exertion in combination with a febrile illness. Malignant hyperthermia susceptible patients are recommended to be vaccinated against flu and restrict physical activities when febrile, wear an MH alert bracelet, and inform medical personnel of their MH history. Oral dantrolene is suggested to be available to MHS patients for administration with the early signs of awake MH.

Keeping Cool When Things Heat Up During a Malignant Hyperthermia Crisis

This article describes the experience of a health care team at a maternity center during their care for a woman exhibiting an atypical presentation of malignant hyperthermia and outlines the steps taken to rapidly identify the condition and begin treatment to save her life. Key components in ensuring a positive outcome in a malignant hyperthermia crisis include increased awareness and readiness to effectively treat and reverse the signs and symptoms of this condition.

Is there a link between exertional heat stroke and susceptibility to malignant hyperthermia?

Objective

The identification of a predisposition toward malignant hyperthermia (MH) as a risk factor for exertional heat stroke (EHS) remains a matter of debate. Such a predisposition indicates a causal role for MH susceptibility (MHS) after EHS in certain national recommendations and has led to the use of an in vitro contracture test (IVCT) to identify the MHS trait in selected or unselected EHS patients. The aim of this study was to determine whether the MHS trait is associated with EHS.

Methods

EHS subjects in the French Armed Forces were routinely examined for MHS after experiencing an EHS episode. This retrospective study compared the features of IVCT-diagnosed MHS (iMHS) EHS subjects with those of MH-normal EHS patients and MH patients during the 2004–2010 period. MHS status was assessed using the European protocol.

Results

During the study period, 466 subjects (median age 25 years; 31 women) underwent MHS status investigation following an EHS episode. None of the subjects reported previous MH events. An IVCT was performed in 454 cases and was diagnostic of MHS in 45.6% of the study population, of MH susceptibility to halothane in 18.5%, of MH susceptibility to caffeine in 9.9%, and of MH susceptibility to halothane and caffeine in 17.2%. There were no differences in the clinical features, biological features or outcomes of iMHS EHS subjects compared with those of MH-normal or caffeine or halothane MHS subjects without known prior EHS episode. The recurrence rate was 12.7% and was not associated with MH status or any clinical or biological features. iMHS EHS patients exhibited a significantly less informative IVCT response than MH patients.

Conclusions

The unexpected high prevalence of the MHS trait after EHS suggested a latent disturbance of calcium homeostasis that accounted for the positive IVCT results. This study did not determine whether EHS patients have an increased risk of MH, and it could not determine whether MH susceptibility is a risk factor for EHS.

Malignant hyperthermia: a review

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that presents as a hypermetabolic response to potent volatile anesthetic gases such as halothane, sevoflurane, desflurane, isoflurane and the depolarizing muscle relaxant succinylcholine, and rarely, in humans, to stressors such as vigorous exercise and heat. The incidence of MH reactions ranges from 1:10,000 to 1: 250,000 anesthetics. However, the prevalence of the genetic abnormalities may be as great as one in 400 individuals. MH affects humans, certain pig breeds, dogs and horses. The classic signs of MH include hyperthermia, tachycardia, tachypnea, increased carbon dioxide production, increased oxygen consumption, acidosis, hyperkalaemia, muscle rigidity, and rhabdomyolysis, all related to a hypermetabolic response. The syndrome is likely to be fatal if untreated. An increase in end-tidal carbon dioxide despite increased minute ventilation provides an early diagnostic clue. In humans the syndrome is inherited in an autosomal dominant pattern, while in pigs it is autosomal recessive. Uncontrolled rise of myoplasmic calcium, which activates biochemical processes related to muscle activation leads to the pathophysiologic changes. In most cases, the syndrome is caused by a defect in the ryanodine receptor. Over 400 variants have been identified in the RYR1 gene located on chromosome 19q13.1, and at least 34 are causal for MH. Less than 1 % of variants have been found in CACNA1S but not all of these are causal. Diagnostic testing involves the in vitro contracture response of biopsied muscle to halothane, caffeine, and in some centres ryanodine and 4-chloro-m-cresol. Elucidation of the genetic changes has led to the introduction of DNA testing for susceptibility to MH. Dantrolene sodium is a specific antagonist and should be available wherever general anesthesia is administered. Increased understanding of the clinical manifestation and pathophysiology of the syndrome, has lead to the mortality decreasing from 80 % thirty years ago to <5 % in 2006.

Hypothesis: exertional heat stroke-induced myopathy and genetically inherited malignant hyperthermia represent the same disorder, the human stress syndrome

Exertional heat stroke is usually experienced as a result of a prolonged and intensive exercise. It is a life-threatening condition that is characterized by an increase in core body temperature and rhabdomyolysis. The associated hyperkalemia and metabolic acidosis may lead to an acute renal, cardiac, and hemostatic failure. Exactly, the same symptoms are noticed in case of the anesthesia-induced malignant hyperthermia (MH), an inherited disorder of the skeletal muscle ryanodine receptor. This receptor is a Ca(2+) channel that is activated by the volatile anesthetic agents and depolarizing muscle relaxant. The presence of MH-associated ryanodine receptor variant in the individuals who suffered from EH and improvement of the symptoms with dantrolene has frequently raised the question as to whether the two disorders actually represent one and the same disease. Nevertheless, an exact explanation of the susceptibility of the genetically predisposed MH individuals to ER remains elusive. We have attempted to review the published clinical reports to explore the possibility that ER and EH represent one and the same disorder.

[Modern diagnostic approaches to malignant hyperthermia susceptibility]

Malignant hyperthermia is a well-known rare life-threatening autosomal-dominant pharmacogenetic disease, The arti- cle deals with a halothane-caffeine contracture test. The test is a model of muscle reaction to triggers in-vitro and it is the "golden standard" for malignant hyperthermia susceptibility (MHS) diagnosis. Genetic analysis is less invasive, but its sensitivity is significantly lower. The review discusses both the methods which are essential to be completely reproduced in Russia, and their role in modern approach to MHS diagnosis.

Increased requirement for minute ventilation and negative arterial to end-tidal carbon dioxide gradient may indicate malignant hyperthermia

Characteristic signs of malignant hyperthermia (MH) include unexplained tachycardia, increased end-tidal carbon dioxide (Etco₂) concentration, metabolic and respiratory acidosis, and an increase in body temperature above 38.8°C. We present the case of a patient with highly probable MH. In addition to sinus tachycardia and metabolic and respiratory acidosis, this patient also had a negative arterial to Etco₂ gradient and an increased requirement for minute ventilation to maintain a normal Etco₂ concentration, with signs of increased CO₂ production. Despite these signs of MH, the patient's rectal temperature monitoring equipment did not show an increase in temperature, although the temperature measured in the mouth was increased. This case illustrates the unreliability of measuring rectal temperature as a means of reflecting body temperature during MH and the usefulness of increased CO₂ production signs in helping to diagnose MH.

3,5-Di-t-butyl catechol is a potent human ryanodine receptor 1 activator, not suitable for the diagnosis of malignant hyperthermia susceptibility

3,5-Di-t-butyl catechol (DTCAT) releases Ca(2+) from rat skeletal muscle sarcoplasmic reticulum (SR) vesicles. Hence, it is a candidate for use as a substitute for halothane or caffeine in the in vitro contracture test for the diagnosis of susceptibility to malignant hyperthermia (MH). To characterize the effect of DTCAT at cell level, Ca(2+) release experiments were performed on cultured, human skeletal muscle myotubes using the fluorescent Ca(2+) indicator fura2-AM. DTCAT was also assayed in the in vitro contracture test on human skeletal muscle bundles obtained from individuals diagnosed susceptible (MHS), normal (MHN) or equivocal for halothane (MHEH) and compared to the standard test substances caffeine and halothane. DTCAT increased, in a concentration-dependent manner and with a higher efficacy as compared to caffeine, the free, intracellular Ca(2+) levels of cultured MHN and MHS skeletal muscle myotubes. This effect was similar in both types of myotubes and involved the release of Ca(2+) from SR stores as well as Ca(2+)-influx from the extracellular space. Inhibition of ryanodine receptors either with ryanodine or with ruthenium red markedly reduced DTCAT-induced increase in intracellular Ca(2+) concentration while abolishing that induced by caffeine. In MHN skeletal muscle bundles, DTCAT induced contractures with an EC(50) value of 160 ± 91 μM. However, the sensitivity of MHS or MHEH muscles to DTCAT was similar to that of MHN muscles. In conclusion, DTCAT is not suitable for the diagnosis of MH susceptibility due to its failure to discriminate between MHN and MHS muscles.

Comparison of the therapeutic effectiveness of a dantrolene sodium solution and a novel nanocrystalline suspension of dantrolene sodium in malignant hyperthermia normal and susceptible pigs

BACKGROUND AND OBJECTIVE

Stopping trigger agents and prompt administration of dantrolene are the cornerstones of treatment of malignant hyperthermia. However, significant time is lost in treatment of the condition because of the cumbersome preparation and administration of the commercially available dantrolene sodium for injection. A potential improvement has become available in the form of a novel nanocrystalline dantrolene sodium suspension (DSS), which is 150 times more concentrated (50 mg ml(-1)) than the standard dantrolene sodium solution (0.33 mg ml(-1)). The aims of this study were to measure the effects of DSS on clinical and laboratory variables in malignant hyperthermia normal pigs and to compare the therapeutic management and clinical effectiveness of DSS with standard dantrolene sodium in a fulminant malignant hyperthermia crisis in susceptible pigs. The pig model is a well accepted method of studying the malignant hyperthermia crisis and is an ideal way to evaluate the variables of interest in this study.

METHODS

Seven malignant hyperthermia normal and 10 malignant hyperthermia susceptible pigs were studied. Malignant hyperthermia susceptible pigs (body weight approximately 24 kg) were allocated to a dantrolene sodium group or a DSS group. After induction of anaesthesia, a 22-gauge catheter was placed in an ear vein and trigger-free anaesthesia was performed. After achieving stable conditions, administration of halothane was started with 0.1% and then 0.15%. Halothane was discontinued after the administration of 0.2% (malignant hyperthermia normal pigs) or when a fulminant malignant hyperthermia crisis was achieved (malignant hyperthermia susceptible pigs). After halothane was discontinued, FIO2 was set to 1.0, respiratory minute volume was doubled and sodium bicarbonate 2 mmol kg(-1) was administered. The time required to prepare and administer each formulation was measured. To simulate the administration of the substances under typical clinical conditions for a child weighing approximately 24 kg, dantrolene sodium (5 mg kg(-1)) or DSS (5 mg kg(-1)) was prepared and injected via the intravenous 22-gauge cannula. Bolus administrations of dantrolene sodium or DSS were repeated after 24 min.

RESULTS

Arterial pH, arterial pCO2, mean arterial pressure and arterial lactate concentration remained stable during the experiment with DSS in malignant hyperthermia normal pigs. A significant decrease in cardiac index and increases in systemic vascular resistance and serum potassium concentration occurred after administration of DSS. In all malignant hyperthermia susceptible animals, the inhaled administration of halothane 0.15% led to a fulminant malignant hyperthermia crisis. The therapeutic regimens with administration of dantrolene sodium or DSS were successful in treating the malignant hyperthermia crisis in all animals. The course of the malignant hyperthermia crisis and the therapeutic effects of dantrolene sodium or DSS were comparable in the two groups. The time needed to prepare DSS for administration was significantly shorter (51 ± 9 s) compared to dantrolene sodium (860 ± 202 s). The time taken to inject DSS (4 ± 2 s) was significantly shorter than for dantrolene sodium (472 ± 51 s).

CONCLUSION

The therapeutic action of DSS in a malignant hyperthermia crisis in pigs was effective and comparable to that of standard dantrolene sodium. However, preparation and administration of DSS were significantly faster, which may offer a clinically significant advantage in the treatment of a fulminant malignant hyperthermia crisis and may result in a reduction in stress for the anaesthesia team.

Basal bioenergetic abnormalities in skeletal muscle from ryanodine receptor malignant hyperthermia-susceptible R163C knock-in mice

Malignant hyperthermia (MH) and central core disease in humans have been associated with mutations in the skeletal ryanodine receptor (RyR1). Heterozygous mice expressing the human MH/central core disease RyR1 R163C mutation exhibit MH when exposed to halothane or heat stress. Considering that many MH symptoms resemble those that could ensue from a mitochondrial dysfunction (e.g. metabolic acidosis and hyperthermia) and that MH-susceptible mice or humans have a higher than normal cytoplasmic Ca(2+) concentration at rest, we evaluated the role of mitochondria in skeletal muscle from R163C compared with wild type mice under basal (untriggered) conditions. R163C skeletal muscle exhibited a significant increase in matrix Ca(2+), increased reactive oxygen species production, lower expression of mitochondrial proteins, and higher mtDNA copy number. These changes, in conjunction with lower myoglobin and glycogen contents, Myh4 and GAPDH transcript levels, GAPDH activity, and lower glucose utilization suggested a switch to a compromised bioenergetic state characterized by both low oxidative phosphorylation and glycolysis. The shift in bioenergetic state was accompanied by a dysregulation of Ca(2+)-responsive signaling pathways regulated by calcineurin and ERK1/2. Chronically elevated resting Ca(2+) in R163C skeletal muscle elicited the maintenance of a fast-twitch fiber program and the development of insulin resistance-like phenotype as part of a metabolic adaptation to the R163C RyR1 mutation.

Identification and functional characterization of malignant hyperthermia mutation T1354S in the outer pore of the Cavalpha1S-subunit

To identify the genetic locus responsible for malignant hyperthermia susceptibility (MHS) in an Italian family, we performed linkage analysis to recognized MHS loci. All MHS individuals showed cosegregation of informative markers close to the voltage-dependent Ca(2+) channel (Ca(V)) α(1S)-subunit gene (CACNA1S) with logarithm of odds (LOD)-score values that matched or approached the maximal possible value for this family. This is particularly interesting, because so far MHS was mapped to >178 different positions on the ryanodine receptor (RYR1) gene but only to two on CACNA1S. Sequence analysis of CACNA1S revealed a c.4060A>T transversion resulting in amino acid exchange T1354S in the IVS5-S6 extracellular pore-loop region of Ca(V)α(1S) in all MHS subjects of the family but not in 268 control subjects. To investigate the impact of mutation T1354S on the assembly and function of the excitation-contraction coupling apparatus, we expressed GFP-tagged α(1S)T1354S in dysgenic (α(1S)-null) myotubes. Whole cell patch-clamp analysis revealed that α(1S)T1354S produced significantly faster activation of L-type Ca(2+) currents upon 200-ms depolarizing test pulses compared with wild-type GFP-α(1S) (α(1S)WT). In addition, α(1S)T1354S-expressing myotubes showed a tendency to increased sensitivity for caffeine-induced Ca(2+) release and to larger action-potential-induced intracellular Ca(2+) transients under low (≤ 2 mM) caffeine concentrations compared with α(1S)WT. Thus our data suggest that an additional influx of Ca(2+) due to faster activation of the α(1S)T1354S L-type Ca(2+) current, in concert with higher caffeine sensitivity of Ca(2+) release, leads to elevated muscle contraction under pharmacological trigger, which might be sufficient to explain the MHS phenotype.

Ryanodine receptor channelopathies

Ryanodine receptors (RyR) are intracellular Ca2+-permeable channels that provide the sarcoplasmic reticulum Ca2+ release required for skeletal and cardiac muscle contractions. RyR1 underlies skeletal muscle contraction, and RyR2 fulfills this role in cardiac muscle. Over the past 20 years, numerous mutations in both RyR isoforms have been identified and linked to skeletal and cardiac diseases. Malignant hyperthermia, central core disease, and catecholaminergic polymorphic ventricular tachycardia have been genetically linked to mutations in either RyR1 or RyR2. Thus, RyR channelopathies are both of interest because they cause significant human diseases and provide model systems that can be studied to elucidate important structure-function relationships of these ion channels.

Role of endotoxin and cytokines in the systemic inflammatory response to heat injury

Environmental heat exposure represents one of the most deadly natural hazards in the United States. Heat stroke is a life-threatening illness that affects all segments of society with few effective treatment strategies to mitigate the long-term debilitating consequences of this syndrome. Although the etiologies of heat stroke are not fully understood, the long-term sequelae are thought to be due to a systemic inflammatory response syndrome (SIRS) that ensues following heat-induced tissue injury. Endotoxin and cytokines have been implicated as key mediators of the heat-induced SIRS, based almost exclusively on correlative data that show high circulating concentrations of these substances in heat stroke patients and animal models. However, endotoxin and cytokine neutralization studies have not consistently supported this hypothesis indicating that the mechanisms of heat stroke morbidity / mortality remain poorly understood. This review discusses the current understanding of the role of endotoxin and cytokines in heat-induced SIRS. Insight is provided into genetic conditions that may predispose to heat stroke and potential therapeutic strategies that may be efficacious against the adverse consequences of this debilitating illness.

[Propofol triggers a marked body temperature increase in a patient with fulminant malignant hyperthermia (MH) without inducing other symptoms of MH]

A 53-year-old woman who had experienced symptoms of fulminant malignant hyperthermia (MH) by sevoflurane a week before and her MH muscle biopsy revealing positive later, underwent the right hemicolectomy under total intravenous anesthesia with propofol and fentanyl. The patient's body temperature increased at a rate of 0.6 degree C per 15 min from 37.5 to 39.4 degrees C, but other symptoms of MH, such as tachycardia, arrhythmia, acidemia, and hypoxemia, were obviously slight in comparison with those induced by sevoflurane. The body temperature decreased after discontinuation of propofol and administration of dantrorene injection. When the patient received continuous propofol infusion for the purpose of sedation in the intensive care unit again, the body temperature gradually increased to 40 degrees C. However, it decreased to 37.8 degrees C after discontinuation of propofol and dantrorene injection again. It is well recognized that propofol is not a MH trigger, but it shoud be noted that some MH patients could experience a hypermetabolic state, such as hyperthermia, even by propofol.

Genetic variation in RYR1 and malignant hyperthermia phenotypes

BACKGROUND

Malignant hyperthermia (MH) is associated, in the majority of cases, with mutations in RYR1, the gene encoding the skeletal muscle ryanodine receptor. Our primary aim was to assess whether different RYR1 variants are associated with quantitative differences in MH phenotype.

METHODS

The degree of in vitro pharmacological muscle contracture response and the baseline serum creatine kinase (CK) concentration were used to generate a series of quantitative phenotypes for MH. We then undertook the most extensive RYR1 genotype-phenotype correlation in MH to date using 504 individuals from 204 MH families and 23 RYR1 variants. We also determined the association between a clinical phenotype and both the laboratory phenotype and RYR1 genotype.

RESULTS

We report a novel correlation between the degree of in vitro pharmacological muscle contracture responses and the onset time of the clinical MH response in index cases (P<0.05). There was also a significant correlation between baseline CK concentration and clinical onset time (P=0.039). The specific RYR1 variant was a significant determinant of the severity of each laboratory phenotype (P<0.0001).

CONCLUSIONS

The MH phenotype differs significantly with different RYR1 variants. Variants leading to more severe MH phenotype are distributed throughout the gene and tend to lie at relatively conserved sites in the protein. Differences in phenotype severity between RYR1 variants may explain the variability in clinical penetrance of MH during anaesthesia and why some variants have been associated with exercise-induced rhabdomyolysis and heat stroke. They may also inform a mutation screening strategy in cases of idiopathic hyperCKaemia.

Calsequestrin-1: a new candidate gene for malignant hyperthermia and exertional/environmental heat stroke

Malignant hyperthermia (MH) and exertional/environmental heat stroke (EHS) in humans present as similar life threatening crises triggered by volatile anaesthetics and strenuous exercise and/or high temperature, respectively. Many families (70-80%) diagnosed with MH susceptibility (MHS), and a few with EHS, are linked to mutations in the gene for the ryanodine receptor type-1 (RyR1), Ca(2+) release channel of the sarcoplasmic reticulum (SR) of skeletal muscle and a key protein in excitation-contraction (EC) coupling. However, mutations in the RyR1 gene are not found in all MH families, suggesting that alternative genes remain to be identified. In our laboratory we have recently characterized a novel knockout model lacking skeletal muscle calsequestrin (CASQ1), a SR Ca(2+)-binding protein that modulates RyR1 function, and investigated whether these mice present a MH/EHS-like phenotype. Ablation of CASQ1 results in remodelling of the EC coupling apparatus and functional changes, which in male mice causes a striking increase in the rate of spontaneous mortality and susceptibility to trigger MH-like lethal episodes in response to halothane and heat stress. The demonstration that ablation of CASQ1 results in MH- and EHS-like lethal episodes validates CASQ1 as a viable candidate gene for linkage analysis in MH and EHS families where mutations in RyR1 are excluded.

Malignant hyperthermia and its implications in general dentistry

Malignant hyperthermia (MH) is an uncommon and potentially life-threatening pharmacogenetic disorder. This abnormality in muscle metabolism can be triggered by a variety of agents (particularly general anesthetics and stress), resulting in a rapid heart rate increase, muscle rigidity, acidosis, temperature elevation, rhabdomyolysis, and renal failure. Immediate discontinuing of triggering agents, oxygenation, cooling, and dantrolene are necessary to treat an episode. MH-susceptible patients often indicate a positive family history of experiencing an adverse event during anesthesia. Few diagnostic tests are available to screen patients; the most accurate test is a skeletal muscle biopsy. MH-susceptible patients can undergo surgical procedures as necessary. Careful exploration of the medical history will allow the clinician to make the necessary modifications to treat and manage an episode expediently.

[Excitation-contraction coupling in skeletal muscle: questions remaining after 50 years of research]

The excitation-contraction coupling mechanism was defined as the entire sequence of reactions linking excitation of plasma membrane to activation of contraction in skeletal muscle. By using different techniques, their regulation and interactions have been studied during the last 50 years, defining until now the importance and origin of the calcium ion as a contractile activator and the main proteins involved in the whole mechanism. Furthermore, the study of the ultrastructural basis and pharmacological regulation of the excitation-contraction coupling phenomenon has begun. The excitation-contraction coupling is thought to be altered in situations as ageing, muscle fatigue and some muscle diseases. However, many questions remain to be answered. For example, (1) How excitation-contraction coupling develops and ages? (2) What role does it play in muscle fatigue and other diseases? (3) What is the nature of the interaction between the proteins believed to be involved? The present review describes excitation-contraction coupling in skeletal muscle and techniques used to better understand it as an introduction for discussing unanswered questions regarding excitation-contraction coupling.

Diagnostics and therapy of muscle channelopathies--Guidelines of the Ulm Muscle Centre

This article is dedicated to our teacher, Prof. Erich Kuhn, Heidelberg, on the occasion of his 88th birthday on 23rd November 2008. In contrast to muscular dystrophies, the muscle channelopathies, a group of diseases characterised by impaired muscle excitation or excitation-contraction coupling, can fairly well be treated with a whole series of pharmacological drugs. However, for a proper treatment proper diagnostics are essential. This article lists state-of-the-art diagnostics and therapies for the two types of myotonic dystrophies, for recessive and dominant myotonia congenita, for the sodium channel myotonias, for the primary dyskalemic periodic paralyses, for central core disease and for malignant hyperthermia susceptibility in detail. In addition, for each disorder a short summary of aetiology, symptomatology, and pathogenesis is provided.

Channels active in the excitability of nerves and skeletal muscles across the neuromuscular junction: basic function and pathophysiology

Ion channels are essential for the basic physiological function of excitable cells such as nerve, skeletal, cardiac, and smooth muscle cells. Mutations in genes that encode ion channels have been identified to cause various diseases and disorders known as channelopathies. An understanding of how individual ion channels are involved in the activation of motoneurons and their corresponding muscle cells is essential for interpreting basic neurophysiology in nerves, the heart, and skeletal and smooth muscle. This review article is intended to clarify how channels work in nerves, neuromuscular junctions, and muscle function and what happens when these channels are defective. Highlighting the human diseases that result from defective ion channels is likely to be interesting to students in helping them choose to learn about channel physiology.

Maligne Hyperthermie

The term "malignant hyperthermia" (MH), regarded as the typical anaesthetic disease, refers to a clinical syndrome of varying intensity (from abortive courses to fulminant crises) and develops only under exposure of certain triggering substances or mechanisms. MH is caused by a defect in the ryanodine receptor subtype 1, which can often be proved genetically. Furthermore, it may also be generated by other mechanisms which disturb the membranous integrity of skeletal muscle cells (e.g. some myotonias, muscular dystrophies, malformation syndromes). Hyperthermia is only one of a number of life-threatening symptoms that may occur during a fulminant crisis, which ultimately results from an excessive release of calcium into the cytoplasm of muscle cells. Due to a current good knowledge about classical triggers, symptoms and therapeutic interventions, a clinical MH presentation may successfully be treated in the perioperative period. However, it appears to be likely that there are unreported cases outside hospitals since atypical courses or alternative MH triggers (e.g. alcohol, drugs, physical stress) may impair the correct diagnosis. In contrast severe hyperthermia can also arise from other drug-induced diseases, e.g. the neuroleptic malignant syndrome or the serotonin syndrome.

Male preponderance of patients testing positive for malignant hyperthermia susceptibility

BACKGROUND

Malignant hyperthermia susceptibility is diagnosed using an in vitro contracture test (IVCT). In families in which the mutation is known, genetic tests are also available. The inheritance pattern is regarded as autosomal dominant, which predicts equal proportions of men and women affected. The aim of this study was to investigate whether there were sex differences in the diagnostic outcome of the 1407 patients tested for malignant hyperthermia in Sweden between 1985 and 2005.

METHODS

Information about sex, diagnosis, IVCT result and kinship was analysed. Comparisons were made between the two sexes. Probands and relatives were analysed separately in order to eliminate bias caused by the type of surgery performed in the two sexes.

RESULTS

Males, more than females, revealed a pathological outcome in IVCT. Amongst male relatives, the fraction of pathological outcome in IVCT was 0.70 [95% confidence interval (CI), 0.66-0.74]; the corresponding value for females was 0.40 (95% CI, 0.36-0.44).

CONCLUSION

A significant difference was observed in the sex distribution of outcome of IVCT, with significantly more males revealing a pathological IVCT. This indicates the influence of one or several factors related to sex in the outcome of IVCT, for example different expression of calcium handling proteins in the sexes, a complex pattern of inheritance or unknown environmental factors.

Calcium channelopathies

Intracellular calcium ([Ca2+]i) is highly regulated in eukaryotic cells. The free [Ca2+]i is approximately four orders of magnitude less than that in the extracellular environment. It is, therefore, an electrochemical gradient favoring Ca2+ entry, and transient cellular activation increasing Ca2+ permeability will lead to a transient increase in [Ca2+]i. These transient rises of [Ca2+]i trigger or regulate diverse intracellular events, including metabolic processes, muscle contraction, secretion of hormones and neurotransmitters, cell differentiation, and gene expression. Hence, changes in [Ca2+]i act as a second messenger system coordinating modifications in the external environment with intracellular processes. Notably, information on the molecular genetics of the membrane channels responsible for the influx of Ca2+ ions has led to the discovery that mutations in these proteins are linked to human disease. Ca2+ channel dysfunction is now known to be the basis for several neurological and muscle disorders such as migraine, ataxia, and periodic paralysis. In contrast to other types of genetic diseases, Ca2+ channelopathies can be studied with precision by electrophysiological methods, and in some cases, the results have been highly rewarding with a biophysical phenotype that correlates with the ultimate clinical phenotype. This review outlines recent advances in genetic, molecular, and pathophysiological aspects of human Ca2+ channelopathies.

Diseases associated with altered ryanodine receptor activity

Mutations in two intracellular Ca2+ release channels or ryanodine receptors (RyR1 and RyR2) are associated with a number of human skeletal and cardiac diseases. This chapter discusses these diseases in terms of known mechanisms, controversies, and unanswered questions. We also compare the cardiac and skeletal muscle diseases to explore common mechanisms.

Genetics of malignant hyperthermia

Study of the genetics of the malignant hyperthermia syndrome began in families in which both malignant hyperthermia (MH) episodes had been experienced and individuals had strongly positive contracture tests diagnostic of susceptibility to MH. Linkage studies associated this MH phenotype to the ryanodine receptor gene (RYR1) at chromosome 19q13.1 in many families. Although the MH phenotype is not always linked to chromosome 19, the RYR1 has remained the focus of experimentation. Other candidate genes exist, but few MH-susceptible families have variants of these genes. Hundreds of MH-susceptible people have variants of RYR1.

Pharmacologic and functional characterization of malignant hyperthermia in the R163C RyR1 knock-in mouse

BACKGROUND

Malignant hyperthermia is a pharmacogenetic disorder affecting humans, dogs, pigs, and horses. In the majority of human cases and all cases in animals, malignant hyperthermia has been associated with missense mutations in the skeletal ryanodine receptor (RyR1).

METHODS

The authors used a "knock-in" targeting vector to create mice carrying the RyR1 R163C malignant hyperthermia mutation.

RESULTS

Validation of this new mouse model of human malignant hyperthermia susceptibility includes (1) proof of transcription of the R163C allele and expression of ryanodine receptor protein in R163C heterozygous and R163C homozygous animals; (2) fulminant malignant hyperthermia episodes in R163C heterozygous mice after exposure to 1.25-1.75% halothane or an ambient temperature of 42 degrees C characterized by increased rectal temperature, respiratory rate, and inspiratory effort, with significant blood biochemical changes indicating metabolic acidosis, ending in death and hyperacute rigor mortis; (3) intraperitoneal pretreatment with dantrolene provided 100% protection from the halothane-triggered fulminant malignant hyperthermia episode; (4) significantly increased sensitivity (decreased effective concentration causing 50% of the maximal response) of R163C heterozygous and homozygous myotubes to caffeine, 4-chloro-m-cresol, and K-induced depolarization; (5) R163C heterozygous and homozygous myotubes have a significantly increased resting intracellular Ca concentration compared with wild type; (6) R163C heterozygous sarcoplasmic reticulum membranes have a twofold higher affinity (Kd = 35.4 nm) for [H]ryanodine binding compared with wild type (Kd = 80.1 nm) and a diminished inhibitory regulation by Mg.

CONCLUSIONS

Heterozygous R163C mice represent a valid model for studying the mechanisms that cause the human malignant hyperthermia syndrome.

Prevention, Recognition, and Management of Nursing Complications in the Intraoperative and Postoperative Surgical Patient

A review of the literature focusing on postoperative complications reveals that the best available tools to the medical and surgical teams are recognition and prevention. This article highlights the more common postsurgical adverse events and discusses methods for preventing and treating these occurrences.

Malignant hyperthermia

Malignant hyperthermia, also known as malignant hyperpyrexia, is a pharmacogenetic condition which can develop during general anaesthesia and can be fatal. The author suggests that more awareness of the condition is needed by ward-based nurses who are involved with patients undergoing surgery. The article describes the management of the condition, the nursing care and the screening available for susceptible patients.

Suspected malignant hyperthermia in a child with laminin alpha2 (merosin) deficiency in the absence of a triggering agent

Malignant hyperthermia (MH) is an inherited disorder of the skeletal muscles that can be triggered by many anesthetic agents. MH has different presentations and manifestations that makes it difficult to diagnose. Patients with laminin alpha2 deficiency have never been reported to be susceptible to MH. We present a suspected MH episode in the absence of classic triggering agents in a 7-year-old boy with laminin alpha2 (merosin) deficiency and congenital muscular dystrophy. The episode was diagnosed using the MH clinical grading scale and responded well to prompt management with dantrolene. We conclude that patients with laminin alpha2 deficiency may be susceptible to MH, and early suspicion and rapid treatment is vital in the management of MH. Anesthesiologists should be prepared to treat MH in susceptible patients even in the absence of a classical triggering agent.

Defective Mg2+ regulation of RyR1 as a causal factor in malignant hyperthermia

In skeletal muscle, Mg(2+) exerts a dual inhibitory effect on RyR1, by competing with Ca(2+) at the activation site and binding to a low affinity Ca(2+)/Mg(2+) inhibitory site. Pharmacological activators of RyR1 must overcome the inhibitory action of Mg(2+) before Ca(2+) efflux can occur. In normal muscle, where the free [Mg(2+)](i) is approximately 1mM, even prolonged exposure to millimolar levels of volatile anesthetics does not initiate SR Ca(2+) release. However, when the cytosolic [Mg(2+)] is reduced below the physiological range, low levels of volatile anesthetic within the clinically relevant range (1mM) can initiate SR Ca(2+) release, in the form of a propagating Ca(2+) wave. In human muscle fibers from malignant hyperthermia susceptible patients, such Ca(2+) waves occur when 1mM halothane is applied at physiological [Mg(2+)](i). There is increasing evidence to suggest that defective Mg(2+) regulation of RyR1 confers susceptibility to malignant hyperthermia. At the molecular level, interactions between critical RyR1 subdomains may explain the clustering of RyR1 mutations and associated effects on Mg(2+) regulation.

Toxin-induced hyperthermic syndromes

Toxin-induced hyperthermic syndromes are important to consider in the differential diagnosis of patients presenting with fever and muscle rigidity. If untreated, toxin-induced hyperthermia may result in fatal hyperthermia with multisystem organ failure. All of these syndromes have at their center the disruption of normal thermogenic mechanisms, resulting in the activation of the hypothalamus and sympathetic nervous systems.The result of this thermogenic dysregulation is excess heat generation combined with impaired heat dissipation. Although many similarities exist among the clinical presentations and pathophysiologies of toxin-induced hyperthermic syndromes, important differences exist among their triggers and treatments. Serotonin syndrome typically occurs within hours of the addition ofa new serotonergic agent or the abuse of stimulants such as MDMA or methamphetamine. Treatment involves discontinuing the offending agent and administering either a central serotonergic antagonist, such as cyproheptadine or chlorpromazine, a benzodiazepine, or a combination of the two. NMS typically occurs over hours to days in a patient taking a neuroleptic agent; its recommended treatment is generally the combination of a central dopamine agonist, bromocriptine or L-dopa, and dantrolene. In those patients in whom it is difficult to differentiate between serotonin and neuroleptic malignant syndromes, the physical examination may be helpful:clonus and hyperreflexia are more suggestive of serotonin syndrome,whereas lead-pipe rigidity is suggestive of NMS. In patients in whom serotonin syndrome and NMS cannot be differentiated, benzodiazepines represent the safest therapeutic option. MH presents rapidly with jaw rigidity, hyperthermia, and hypercarbia. Although it almost always occurs in the setting of surgical anesthesia, cases have occurred in susceptible individuals during exertion. The treatment of MH involves the use of dantrolene. Future improvements in understanding the pathophysiology and clinical presentations of these syndromes will undoubtedly result in earlier recognition and better treatment strategies.

Malignant hyperthermia

Malignant hyperthermia (MH) is a rare genetic condition which may manifest for the first time during anaesthesia associated with a routine surgical procedure. Characterised initially by muscle rigidity, increased body temperature and metabolic acidosis, the syndrome may prove fatal unless prompt, effective treatment is administered. The sudden development of MH constitutes a medical emergency; hence it is essential that theatre practitioners are knowledgeable about the presenting symptoms and management of the condition.

Cumulative and Bolus In Vitro Contracture Testing with 4-Chloro-3-Ethylphenol in Malignant Hyperthermia Positive and Negative Human Skeletal Muscles

In this study we evaluated the in vitro effects of 4-chloro-3-ethylphenol (CEP) using cumulative (12.5-200 micromol/L) or bolus (75 and 100 micromol/L) administrations, on muscle specimens from malignant hyperthermia (MH) susceptible and MH nonsusceptible patients, respectively. In the cumulative CEP in vitro contracture test, contractures were significantly greater in the MH susceptible compared with the MH nonsusceptible muscles in all concentrations between 25 and 100 micromol/L. There was no overlap between the diagnostic groups at 75 micromol/L of CEP, so this test appears to be feasible for diagnosis of MH susceptibility. The two bolus tests are not diagnostically useful, as overlaps between the diagnostic groups were observed.

Phosphodiesterase-III-inhibition with amrinone leads to contracture development in skeletal muscle preparations of malignant hyperthermia susceptible swine

BACKGROUND AND OBJECTIVE

The phosphodiesterase-III (PDE-III) inhibitor enoximone-induced marked contractures in skeletal muscle specimens of malignant hyperthermia (MH) susceptible (MHS) human beings and swine. Whether this is a substance specific effect of enoximone or caused by inhibition of PDE-III remained unclear. Therefore, the effects of the PDE-III inhibitor amrinone in porcine MH normal (MHN) and MHS skeletal muscles were investigated.

METHODS

MH-trigger-free general anaesthesia was performed in eight MHS and eight MHN swine. The MH status of the swine was determined by detection of the Arg615-Cys point mutation on chromosome 6 indicating MH susceptibility. Skeletal muscle specimens were excised for the in vitro contracture tests with amrinone. Amrinone was added cumulatively every 5 min to muscle specimens in order to obtain organ bath concentrations between 20 and 400 micromol L(-1). The in vitro effects of amrinone on muscle contractures and twitches were measured.

RESULTS

Amrinone-induced contractures in all skeletal muscle preparations. MHS muscles developed contractures at significantly lower bath concentrations of amrinone than MHN muscles. Contractures of MHS compared to MHN muscles were significantly larger at bath concentrations of 80, 100, 150, 200 and 400 micromol L(-1) amrinone. Muscle twitches remained unchanged up to and including 200 micromol L(-1) amrinone.

CONCLUSIONS

Inhibition of PDE-III in general elicited higher contractures in MHS than in MHN muscles. Therefore, a contribution of PDE-III and the cyclic adenosine monophosphate (cAMP) system in the pathophysiology of MH must be suspected.

Malignant hyperthermia: update on susceptibility testing

Malignant hyperthermia (MH) is a pharmacogenetic clinical syndrome that manifests as a hypermetabolic crisis when a susceptible individual is exposed to an anesthetic triggering agent. Clinical signs include unexplained elevation of end-tidal carbon dioxide, muscle rigidity, acidosis, tachycardia, tachypnea, hyperthermia, and evidence of rhabdomyolysis. This process is a result of an abnormally increased release of calcium from the sarcoplasmic reticulum, which is often caused by an inherited mutation in the gene for the ryanodine receptor (RYR1) that resides in the membrane of the sarcoplasmic reticulum. The gold standard for determination of MH susceptibility is the caffeine-halothane contracture test. However, it is invasive, requiring skeletal muscle biopsy and is not widely available. Researchers have begun to map mutations within the ryanodine receptor gene (chromosome 19q13.1) responsible for conferring MH susceptibility. Ryanodine receptor mutations are found in at least 25% of known MH susceptible individuals in North America. Mutation analysis has recently become available in the United States and is expected to play an integral role in the diagnosis of MH susceptibility in the future.

Ryanodine contracture threshold times for diagnosis of malignant hyperthermia susceptibility: an experimental approach from a single laboratory

STUDY OBJECTIVES

To define threshold times for ryanodine contracture testing (RCT) using skeletal muscle specimens from malignant hyperthermia-susceptible (MHS) and control individuals.

DESIGN

Prospective study.

SETTING

Malignant hyperthermia (MH) laboratory at a university hospital.

PATIENTS

8 patients with previous fulminant MH and 53 control patients undergoing in vitro contracture test (IVCT) for diagnosis of MH susceptibility.

INTERVENTIONS

Biopsies of the quadriceps femoris muscle were performed with a 3-in-1 nerve block, with spinal anesthesia, or with trigger-free general anesthesia.

MEASUREMENTS AND MAIN RESULTS

Patients were classified as MHS, MH normal (MHN), or MH equivocal (MHE) by the IVCT according to the protocol of the European MH Group (EMHG). Ryanodine 1 microM was added as a bolus to the organ bath to extra vital muscle specimens. Contracture levels were defined as: 1 = start of contracture (OT; min); 2 = time (min) to reach a contracture of 2 mN, and 3 = time (min) to reach a contracture of 10 mN. The effects of ryanodine on contracture responses were measured. Ryanodine induced contractures in all specimens. MHS specimens reached all defined contracture levels significantly sooner than did the controls. Ryanodine contracture test enables a clear discrimination of MHS specimens from controls at contracture levels of OT and 2 mN, whereas at 10 mN a small overlap was observed.

CONCLUSIONS

Using this test, which is an experimental approach from a single laboratory, an assignment to MHS or MHN is possible. To define contracture levels for RCT more precisely and to agree on commonly used thresholds, multicenter studies with larger numbers of patients are required.

Movement disorder emergencies

Movement disorders may present acutely, and failure to recognize and exclude important differential diagnoses can result in significant morbidity or mortality. Unfortunately, much of the literature pertaining to this topic is scattered and not easily accessible. This review aims to address this deficit. Movement disorder emergencies are discussed according to their most likely mode of presentation. Diagnostic considerations and early management principles are reviewed, along with appropriate pathophysiology where relevant.

Malignant hyperthermia: pathophysiology, clinical presentation, and treatment

Malignant hyperthermia (MH) was first described as an inherited highly lethal disorder in 1960. There has since been significant progress in the clinical management, identification of MH susceptible (MHS) persons, and understanding of the underlying pathophysiology. When patients are known to be MHS prior to surgery, an MH episode can easily be avoided by the use of safe nontriggering anesthetic agents. Current MH mortality is <10%, but many experts believe this can be significantly reduced by improved MH preparedness. MH is triggered in humans by an MH triggering anesthetic agent, which causes the release of calcium from the sarcoplastic reticulum of the skeletal muscle cell at an uncontrolled rate resulting in a hypermetabolic state. Recent molecular genetic studies have shown that MH is related to an abnormal ryanodine receptor that controls the release of calcium from the sarcoplastic reticulum. This article reviews the current understanding of the pathophysiology, diagnosis, clinical presentation, and treatment of MH.

L-type Ca2+ channels in Ca2+ channelopathies

Voltage-gated L-type Ca2+ channels (LTCCs) mediate depolarization-induced Ca2+ entry in electrically excitable cells, including muscle cells, neurons, and endocrine and sensory cells. In this review we summarize the role of LTCCs for human diseases caused by genetic Ca2+ channel defects (channelopathies). LTCC dysfunction can result from structural aberrations within pore-forming alpha1 subunits causing incomplete congenital stationary night blindness, malignant hyperthermia sensitivity or hypokalemic periodic paralysis. However, studies in mice revealed that LTCC dysfunction also contributes to neurological symptoms in Ca2+ channelopathies affecting non-LTCCs, such as Ca(v)2.1 alpha1 in tottering mice. Ca2+ channelopathies provide exciting molecular tools to elucidate the contribution of different LTCC isoforms to human diseases.

Is There a Link between Malignant Hyperthermia and Exertional Heat Illness?

Exertional heat illness (EHI) and malignant hyperthermia (MH) are two potentially lethal conditions. It has been suggested that a subset of MH susceptible persons may be predisposed to EHI. We examine the current understanding of these disorders and explore evidence of a relationship. Screening for the muscle type I ryanodine receptor gene should help clarify the relationship between MH and EHI.