North American Malignant Hyperthermia Group Research Articles

Genetic Mutation Characterized in Malignant Hyperthermia Canine Population

Genetic Mutation Characterized in Malignant Hyperthermia Canine Population. Roberts et al. (page 716)In pigs and in up to 50% of humans who experience malignant hyperthermia (MH) events, the disorder has been linked to mutations in the calcium release channel of the sarcoplasmic reticulum, also known as the ryanodine receptor 1 (RyR1). To determine the molecular basis of canine MH, Roberts et al. established a breeding colony by mating a male mixed-breed dog that was MH-susceptible (MHS) and had survived an in vivo halothane–succinylcholine challenge to three unaffected females, producing four litters. Two additional litters were produced by back-crossing to an unaffected daughter and by mating an MHS son to an unaffected female. Of the total of 47 dogs produced from this breeding program, 31 were subjected to a halothane–succinylcholine challenge in an effort to trigger an MH event. The researchers also biopsied specimens of gracilis muscle obtained from all 47 dogs to determine whether they were MHS or MH normal (MHN) according to the North American Malignant Hyperthermia Group’s test protocol for establishing MH (the in vitro contracture test with halothane and caffeine).During the in vivo challenge, tachycardia, hyperthermia, and hypercapnia developed in 24 dogs, establishing them as MHS. (In contrast to pigs and humans with MH, dogs do not exhibit lactic acidemia, metabolic acidosis, or extensor rigidity.) With the in vitro contracture test, 23 dogs were MHS, 19 were MHN, and 5 were indeterminate. Animals were then tested for linkage to the MHS phenotype. Results of the mutational analysis showed that MH susceptibility in this study colony was transmitted as an autosomal dominant trait. All MHS dogs were heterozygous for the new T1640C mutation found on chromosome 1. None of the MHN dogs carried this mutation. Detection of this mutant allele by clinical challenge and in vitro contracture testing suggests that a dog model may be useful for developing improved phenotypic detection of heterozygotes needed for human diagnosis and genetic investigations.

Screening of Tissue from Malignant Hyperthermia–susceptible Patients Reveals Novel Genetic Mutations

Screening of Tissue from Malignant Hyperthermia–susceptible Patients Reveals Novel Genetic Mutations. Sambuughin et al. (page 594)More than 20 ryanodine receptor 1 (RyR1) mutations have been identified in families with an inherited susceptibility to malignant hyperthermia (MH). Sambuughin et al. obtained skeletal muscle samples from 73 unrelated people with diagnoses of MH susceptibility by using the caffeine–halothane contracture test of the North American Malignant Hyperthermia Group. The patients had been referred for the test because of either a positive family history of MH or development of signs of MH during anesthesia.The muscle samples were collected during a period of 3 yr and were stored at −70°C. Genomic DNA was extracted from stored muscle tissue or peripheral blood and was amplified using standard polymerase chain reaction–based restriction fragment length polymorphism, single-strand conformation polymorphism, and sequencing analysis. Most of the known RyR1 mutations were analyzed using the restriction fragment length polymorphism method, whereas new mutations were searched by single-strand conformation polymorphism in exons 12, 15, 39, 40, 44, 45, and 46 of the gene. Seven known RyR1 mutations were detected at frequencies ranging from 1.4% to 5.5%. The research team also detected three novel amino acid substitutions, at frequencies of 1.4% each. All 10 mutations were in 16 unrelated individuals and account for 21.9% of the screened North American MH-susceptible population. Statistical correlation between caffeine–halothane contracture test phenotypes and RyR1 was not studied because of the small number of subjects carrying the same mutation and lack of family members for the study. The frequency and distribution of RyR1 gene mutations detected in this North American MH-susceptible population were different from those previously identified in Western Europe. Larger-scale studies are needed, say the authors, to assess the type and frequency of mutations in RyR1 associated with MH in the North American population.

Comparison of the in vitro caffeine-halothane contracture test with the Ca-induced Ca release rate test in patients suspected of having malignant hyperthermia susceptibility.

We compared the results of the in vitro caffeine-halothane contracture test (CHCT) according to the protocols of the North American Malignant Hyperthermia Group (NAMHG) and the European Malignant Hyperthermia Group (EMHG) with the Ca-induced Ca release (CICR) rate test in the same patients with suspected malignant hyperthermia (MH). Five normal controls and 16 patients suspected of having MH susceptibility were studied. Muscle biopsies were usually obtained from the musculus vastus lateralis. Diagnostic cutoff points and procedures for CHCT protocols were as described in the original and renewal versions of NAMHG and EMHGs. The CICR rate test was performed according to the protocol reported by Endo et al. All five normal controls and two patients with abortive MH, two with postoperative hyperthermia, and three with high serum creatine kinase levels were normal in the three tests. Three patients with MH reactions and one patient with a history of masseter spasm were classified as MH positive according to NAMHG criteria and MH susceptible and MH equivocal according to EMHG criteria. There were five cases with discordant results between the CHCT and CICR rate tests. We propose that muscle biopsy for diagnosis of MH susceptibility should combine the CHCT with the CICR rate test, which may identify the defective site of Ca release channels.

Comparison Between the European and North American Protocols for Diagnosis of Malignant Hyperthermia Susceptibility in Humans

We compared the diagnostic outcome of in vitro contracture tests for diagnosis of malignant hyperthermia susceptibility performed according to the European Malignant Hyperthermia Group protocol and the North American Malignant Hyperthermia Group protocol.The aim of the study was to compare the two major diagnostic tests of malignant hyperthermia susceptibility to have basic data for a common worldwide protocol. We evaluated 156 patients and 17 control individuals. The accordance in diagnostic outcome was 87%. The diverging outcomes between the two protocols were found in a group of patients reacting in few muscle strips and close to the cutoff limits. A 100% accordance in diagnostic outcome was found in individuals with contractures in at least five of six tested muscle strips. In both protocols, contractures close to the cutoff limits in a few muscle strips in scientific studies should be considered as unknown results. Implications: We compared the two major protocols for investigating malignant hyperthermia susceptibility. There was 87% accordance in diagnostic outcome. The diverging outcomes were seen in individuals with less reproducible test results near the cutoff limits. In scientific studies, such results should be considered as unknown. (Anesth Analg 1999;88:1155-60)

Effect of temperature variation (22˚C- 44˚C) on halothane and caffeine contracture testing in normal humans

Malignant hyperthermia (MH) susceptibility is diagnosed using halothane-caffeine contracture testing of a muscle sample maintained at 37 degrees C. However, there has not been a systematic study that examines the effect of different temperatures on the response of normal muscle to halothane and caffeine. We hypothesized that altering bath temperature would modify the contracture responses. We obtained muscle samples from 20 patients undergoing surgical procedures of the lower extremities. The samples were dissected into 245 bundles and the bundles were exposed to halothane 3% or incremental caffeine, according to the North American MH group protocol. Several bundles from each patient were simultaneously studied at four different temperatures (22 degrees C, 30 degrees C, 37 degrees C and 44 degrees C). Each bundle was studied at only one temperature, the muscle samples of 3 patients were simultaneously studied at all four temperatures for halothane and caffeine. Maximum contracture to caffeine (32 mM) was highest at 37 degrees C; however, at lower caffeine concentrations (2-4 mM), there was no consistent effect of temperature on contracture response. Likewise, temperature did not alter contracture responses to halothane. The extremes of temperature (22 degrees C and 44 degrees C) were associated with lack of twitch in response to electrical stimulation. For the bundles exposed to halothane at 22 degrees C, the absence of a twitch was associated with the presence of a contracture, although these were never above the diagnostic threshold. We conclude that temperature has little effect on responses of normal muscle to halothane and caffeine.

Malignant hyperthermia testing in patients with persistently increased serum creatine kinase levels.

We describe 49 neurologically asymptomatic patients with persistently increased serum creatine kinase (CK) levels (idiopathic hyperCKemia or IHCK) who were referred to our institution for diagnostic muscle biopsy, including malignant hyperthermia (MH) susceptibility testing between 1979 and 1993. Muscle biopsy samples of the vastus lateralis were obtained for histologic analysis and MH contracture testing with halothane and caffeine. From 1979 to November 1987, patients were tested for MH in accordance with a standardized institutional protocol. After November 1987, contracture testing was performed according to the recently adopted North American MH Group protocol. In both protocols, a patient was considered to be MH susceptible (MHS) if one or more muscle strip demonstrated an abnormal contracture response after exposure to 3% halothane, 2% halothane, or caffeine alone. Twenty-four of the 49 IHCK patients (49%) had positive contracture tests. No significant correlation was found between the magnitude of CK increase and the incidence of MHS or histologic abnormalities. Unexplained persistently increased CK levels in an otherwise healthy patient should alert the anesthesiologist to the possibility of MHS and/or myopathy.

Genotype and phenotype relationships for mutations in the ryanodine receptor in patients referred for diagnosis of malignant hyperthermia

Anaesthesia-induced malignant hyperthermia (MH) may be caused by specific gene defects in the skeletal muscle ryanodine receptor. We have studied the frequency of occurrence of the C1840T mutation, analogous to the porcine mutation, and three mutations associated both with MH and central core disease (G7301A, C487T and C1209G). We investigated skeletal muscle specimens from up to 137 patients testing negative and 101 patients testing positive for MH susceptibility by the North American MH Group protocol. The presence or absence of the mutations was determined by polymerase chain reaction and restriction enzyme digestion. The frequencies of occurrence of the C1840T and C487T mutations were 2% and 1%, respectively, in MH-positive subjects and were the only two mutations identified. One subject with central core disease did not have any of the three mutations examined associated with this disorder. Therefore, the porcine and central core disease-associated mutations examined in the ryanodine receptor account for a small proportion (approximately 3%) of MH-positive diagnoses. The mutations examined did not occur in any of the MH-negative patients, supporting an association between defects in the ryanodine receptor and a positive diagnosis for MH.(ABSTRACT TRUNCATED AT 250 WORDS)

International Malignant Hyperthermia Workshop and Symposium

International Malignant Hyperthermia Workshop and Symposium

Malignant Hyperthermia During Sevoflurane Administration

Malignant Hyperthermia During Sevoflurane Administration

Effect of cocaine on the contracture response to 1% halothane in patients undergoing diagnostic muscle biopsy for malignant hyperthermia.

Two case reports have cited the recreational use of cocaine as possible trigger of a malignant hyperthermia (MH) crisis. We evaluated whether toxic concentrations of cocaine altered the in vitro muscle response to halothane during contracture tests for MH. Twenty-two patients were studied. Muscle biopsies were obtained and first tested for MH susceptibility with 3% halothane and caffeine contracture testing. Ten patients were diagnosed as MH-susceptible and 12 as MH non-susceptible, in accordance with the North American Malignant Hyperthermia Group protocol. Then, muscle strips were exposed to 1% halothane in the presence and absence of 0.1 mmol.L-1 cocaine. Cocaine alone did not affect baseline muscle tension in either group. With 1% halothane, MH non-susceptible muscle showed no contracture with or without cocaine. In contrast, in the presence of 1% halothane, MH-susceptible muscle showed either no change in contracture (six patients), an increase (two patients), or a decrease (two patients) when exposed to cocaine. However, the overall effect of cocaine on muscle contracture in the presence of 1% halothane was insignificant in both groups. We conclude that cocaine, even at toxic levels, does not have a direct effect on skeletal muscle contractility and thus is safe for MH-susceptible patients.

Masseter Muscle Rigidity and Malignant Hyperthermia Susceptibility in Pediatric Patients An Update on Management and Diagnosis

Controversy exists regarding the definition of masseter muscle rigidity (MMR) and anesthetic management after MMR. This study reports current anesthetic management after MMR, estimates the incidence of clinical malignant hyperthermia (MH) in patients with MMR, and is the first to evaluate the coincidence of MMR with malignant hyperthermia susceptibility (MHS) according to the 1987 North American Malignant Hyperthermia Group protocol. Practicing anesthesiologists referred pediatric patients for biopsy between 1986 and 1991 based on evidence of MMR after succinylcholine (1975-1991). The clinical scenario was described as MMR alone or MMR followed by signs of MH, including arterial CO2 tension > 50 mmHg, arterial pH < or = 7.25, and base deficit > 8. Patients had caffeine-halothane muscle contracture testing to determine MHS. Seventy patients (50 boys and 20 girls) were evaluated. Eighty-three percent (58 of 70) of anesthetics were halothane-succinylcholine. In 68% (48 of 70) of cases, the anesthetic was discontinued, whereas anesthesia was continued with nontriggering agents in 11% (8 of 70) and with triggering agents in 13% (9 of 70). Fifty-nine percent (41 of 70) of patients were diagnosed as MHS by muscle biopsy. In 7% (5 of 70) of patients, clinical MH developed within 10 min of MMR. This study, by using the current North American Malignant Hyperthermia Group protocol, reaffirms the high incidence (59%, 41 of 70) of MHS associated with MMR as confirmed by muscle biopsy. Of the MHS patients, 5 developed signs of clinical MH. Most anesthesiologists in this study, when confronted with MMR, discontinued anesthesia. Because of the potential lethality of MH and the > 50% concordance between MMR and MHS, the most conservative course of action after MMR is to discontinue the anesthetic and observe the patient for clinical evidence of MH. An acceptable alternative, depending on the urgency of the surgery, would be to continue anesthesia with nontriggering agents for MH, with appropriate monitoring.

Comparison of North American and European malignant hyperthermia group halothane contracture testing protocols in swine

Different in vitro halothane testing procedures have been used in the European malignant hyperthermia (MH) Group Protocol (EMHGP) and the North American MH Group Protocol (NAMHGP), whereas the caffeine-testing protocols are very similar. The present study compares the two halothane-testing protocols in ten MH susceptible swine and in four control swine. Halothane contracture testing was conducted in vitro 12-52 days following the barnyard challenge that established the MH susceptibility of the swine. There was one false positive and one false negative halothane test by the EMHGP. The MH-equivocal category in the EMHGP, which is treated clinically as MH-susceptible, affords a margin of safety in such cases. In contrast, there were no false halothane tests by the NAMHGP. While some skeletal muscle strips from MH pigs were normal by both protocols (NAMHGP 30%; EMHGP 10%), the outcome of halothane testing by the NAMHGP was unaffected. The response to halothane 3% is reduced if preceded by the EMHGP, suggesting that simply adding halothane 3% to the end of the EMHGP does not permit a direct quantitative comparison to the NAMHGP. However, the diagnostic outcomes of the two approaches are similar.

Caffeine and Halothane Contracture Testing in Swine Using the Recommendations of the North American Malignant Hyperthermia Group

Caffeine and halothane contracture testing is widely used to detect malignant hyperthermia (MH) susceptibility. The accuracy and reliability of the 3% halothane test and the incremental caffeine test, as recommended by the North American MH Group, were assessed in 11 swine (five MHS, six control). Nine swine were tested twice, 4-6 weeks apart. Accuracy of the in vitro diagnosis was also assessed by in vivo anesthetic challenge. Of all muscle bundles from MH-susceptible swine, 65% reacted positively to 3% halothane and 70% to 2 mM caffeine. Only 35% had a positive caffeine-specific concentration, and 25% developed an increase in baseline tension greater than or equal to 7% at 2 mM caffeine. However, when only the most positive response to 3% halothane or to 2 mM caffeine was used (a minimum of three fresh muscle strips is recommended), these two tests were highly sensitive and specific. In control swine one of 30 muscle bundles reacted positively to 3% halothane. A positive caffeine-specific concentration developed in one of 25 control muscle bundles exposed to caffeine. The variability in the results of these tests mandated that at least three muscle bundles be used for each test. Nonviable muscle bundles could not be relied upon to provide accurate results. In this porcine model, MH susceptibility could be detected by performing the Caffeine Halothane Contracture Test (CHCT) according to the guidelines of the North American MH Group. However, only the 3% halothane test and the response to 2 mM caffeine produced adequate diagnostic results in this breed of swine.