Skeletal muscle contraction characteristics in vivo in malignant hyperthermia susceptible subjects

Ten malignant hyperthermia susceptible (MHS) subjects were investigated, all of them positive in in vitro tests. As a control group 12 healthy subjects were investigated. The investigation was done in a blind fashion during strictly standardized conditions. Electromechanical delay of contraction and half contraction time to tetanus were faster (P less than 0.05) while half relaxation time was shorter in the MHS subjects (P less than 0.05). Skin and intramuscular temperature were significantly higher in the MHS subjects (P less than 0.05). This indicates that MHS subjects differ in various skeletal muscle characteristics during "normal" conditions. Further studies to define the temperature level at which the test of muscle function is most discriminating are needed before it can be used for diagnostic purposes.     

Caffeine impairs intramuscular energy balance in patients susceptible to malignant hyperthermia

Malignant hyperthermia (MH) is a metabolic myopathy with an abnormal release of calcium by the sarcoplasmic reticulum (SR), triggered by volatile anesthetics and succinylcholine. Similarly, caffeine enhances Ca(2+)release by the SR in vitro. In a prospective, randomized study, high-energy phosphates were studied by intramuscular 31-phosphorus magnetic resonance spectroscopy ((31)P-MRS) in 10 MH-susceptible (MHS) and 7 MH-nonsusceptible (MHN) subjects before and after injection of 0.5 ml caffeine (20 mM). Intramuscular energy balance, measured by the ratios of P(i)/PCr and P(i)/gamma-ATP, did not differ between MHS and MHN patients before and after intramuscular caffeine injection. However, within each group, P(i)/PCr and P(i)/gamma-ATP increased significantly only in the MHS group. Intramuscular caffeine injection seemed to impair the metabolic balance in MHS individuals. This may reflect a local calcium overload leading to consumption of high-energy phosphates and increase of inorganic phosphate. Intramuscular stimulation by caffeine and (31)P-MRS may provide a valuable tool to investigate MH-related metabolic disturbances.     

Myophosphorylase B deficiency and malignant hyperthermia

A 6-year-old boy was examined with the dual purpose of establishing whether he had malignant hyperthermia (MH) and to investigate his complaint of excessive muscle fatiguability. In the course of such investigations, McArdle's disease was diagnosed, and the patient was also identified as an MH-positive reactor.     

Concurrence of malignant hyperthermia and congenital abnormalities

Two children about to undergo corrective surgery were required to be investigated for malignant hyperthermia (MH). These investigations arose out of concern by the anesthetist who had obtained a history of unexplained pyrexial reactions to anaesthetic in other members of the family. Because over the years we have encountered several children with multiple congenital abnormalities who have been found to be susceptible to MH, we stressed the advisability of biopsying not only the patient but also the patient's parents. Positive responses for MH were obtained in the patients and in one of the parents on each occasion. The hypothesis of intrauterine MH with its pharmacogenetic propensity for heat production is considered as a possible etiological factor which may cause abnormalities of a congenital nature.     

Clinical and muscle biopsy findings in malignant hyperthermia susceptibility

Patients (155) were investigated for malignant hyperthermia susceptibility (MHS), by in vitro testing of muscle taken from the vastus medialis muscle. Histopathological and histochemical investigation of muscle was also performed. Ultrastructural investigation was performed in 13 MHS patients; 90% of the patients replied to a questionnaire concerning present or previous neuromuscular symptoms. The majority of MHS and MH negative (MHN) patients had no or only minor histopathological and histochemical abnormalities. Core-targetoid fibres were the only potentially important abnormalities found in MHS patients. There were no differences in neuromuscular symptoms between MHS, MHN and control patients, and most patients in both the MHS and MHN group were normal on clinical examination.     

Carnitine palmitoyl transferase deficiency in malignant hyperthermia

The activity of carnitine palmitoyl transferase, an enzyme that catalyzes the transport of long-chain acylcarnitines into mitochondria, was quantitated in EB-virus-transformed lymphoblasts from 7 patients with susceptibility for malignant hyperthermia. Immunoreactive enzyme protein was also measured using an enzyme-linked immunosorbent assay. Cell lines derived from patients with carnitine palmitoyl transferase deficiency of muscle and from normal individuals were used as positive and negative controls, respectively. One patient with malignant hyperthermia had a deficiency in the enzyme activity which was comparable with that of the known carnitine palmitoyl transferase deficient patients. This individua?s lymphoblasts were also deficient in immunoreactive enzyme protein. All of the remaining patients with malignant hyperthermia were deficient only when the backward assay for carnitine palmitoyl transferase was used for quantitation. It is likely that a subset of individuals with a malignant hyperthermia phenotype have a primary deficiency of carnitine palmitoyl transferase and that others have a milder enzyme deficiency secondary to the primary defect in malignant hyperthermia. © 1993 John Wiley & Soncs, Inc.     

Ankle dorsiflexor twitch properties in malignant hyperthermia

A noninvasive method to diagnose malignant hyperthermia (MH) was sought. To this end, in vivo isometric twitch properties of the ankle dorsiflexor muscles were studied in three groups: (1) MH-susceptible patients (n = 12), (2) relatives (n = 12) of MH-susceptible patients who were judged to be MH resistant, and (3) a group of normal volunteers (n = 42) chosen from the community. Twitch properties were studied under resting state conditions and with 1 or 2 Hz stimulation to produce the negative staircase twitch response. There was a high degree of overlap between the ranges of the measured twitch parameters of all groups. Thus, the techniques presented in this study have no value in diagnosing susceptibility to MH. Several physiological features of human isometric twitch properties were demonstrated: (1) slowing of twitch speed with advancing age, (2) strong positive correlation between body weight and twitch torque, and (3) a negative staircase response typical of that described in other mammalian twitch studies.     

The in vitro determination of susceptibility to malignant hyperthermia

To evaluate the reliability of the in vitro contracture test for susceptibility to malignant hyperthermia, we studied muscles from normal pigs and those susceptible to malignant hyperthermia. We performed the contracture test with various muscles from the same animal. Trapezius and intercostal muscles gave similar results, whereas the extensor digiti II muscle had lower sensitivities to both caffeine and halothane. Thus, the muscle chosen to determine susceptibility to malignant hyperthermia is important. In several animals, a false negative diagnosis would have resulted if only the distal muscle had been studied, and this was true even if weak contractures (less than 200 mg) were considered significant. In addition, we compared the response to caffeine or halothane of cut and intact muscle fibers. Although the cut fibers were depolarized, the sensitivity to these drugs was unchanged. Hence, results of the in vitro contracture test are independent of the resting membrane potential.     

Multiple-pulse stimulation and dantrolene in malignant hyperthermia

A potentially fatal condition, yet preventable, malignant hyperthermia (MH) lacks a satisfactory noninvasive diagnostic test. Studying the effects of intravenous dantrolene (3 mg/kg) on electrically stimulated skeletal muscle, we found that this approach does not conclusively distinguish between normal humans and those susceptible to malignant hyperthermia but nonetheless yielded important information about the action of dantrolene in man and in MH. Supramaximal single- and multiple-pulse stimulation of the common peroneal nerve produced stable torque responses of the dorsiflexor muscles (monitored in vivo), which dantrolene suppressed. With the multiple-pulse stimulation (5-6 pulses) this torque suppression was significantly less in MH-susceptible subjects than in control subjects. This distinction, also observed in MH swine, confirms this animal as a good model for human MH. That dantrolene's effect in MH can be more completely reversed with high frequency stimulation is intriguing; presumably, excitation-contraction coupling differs in MH and normal muscle.     

Analysis of sarcoplasmic reticulum proteins in patients susceptible to malignant hyperthermia

It has been suspected that the cause of malignant hyperthermia (MH) is an abnormality in the sarcoplasmic reticulum of skeletal muscle. We isolated the sarcoplasmic reticulum from malignant hyperthermia-susceptible (MHS) patients and controls and analysed the protein composition with sodium dodecyl sulfate polyacrylamide gel electrophoresis. There were no remarkable changes in the sarcoplasmic reticulum protein composition profile of the scanned gel of the patients. Quantitative measurement of the relative proportion of each band in the gel, however, revealed a slight decrease in calsequestrin and a slight increase in a protein of molecular wieght 23,000. (Ca²⁺ Mg²⁺) ATPase had no altered sub-fragments in MHS patients. Crude mitochondrial proteins and myoplasmic proteins showed minor alterations in composition in some patients. The data supported the thesis that malignant hyperthermia is due to defects in several different cell membranes including the sarcoplasmic reticulum and the mitochondria.     

Porcine malignant hyperthermia: Genotype and contractile threshold of immature muscles

We investigated whether malignant hyperthermia (MH)-related contractile abnormalities, such as lowered contractile threshold, were expressed in MH-susceptible (MHS) immature muscles and myotubes. Muscles from neonatal piglets homozygous for Arg⁶¹⁵ (normal) or for Cys⁶¹⁵ (MHS) ryanodine receptor alleles, and heterozygotes were used. Intact cell bundles from piglet muscles generally were similar in contractile properties to adult muscles of the same genotype. Thresholds for K contractures in normal, heterozygous, and MHS piglet muscles (40 mmol/L, 25 mmol/L and 15 mmol/K⁺, respectively) differed significantly. Cultured myotubes were subjected to a series of square pulses of varying strengths (−50 to +50 mV) and durations (25–300 ms) using whole cell patch-clamp techniques. Threshold for contraction differed significantly among the three genotypes, for example, with 300 msec pulses thresholds were −6.9 ± 0.9, −12.4 ± 1.6, and −22.6 ± 2.6 mV for normal, heterozygous, and MHS myotubes, respectively. Thus, a significantly lower- than- normal threshold for contraction was expressed in MHS and heterozygous piglet muscles and myotubes. Furthermore, these developmentally immature preparations are likely to express other differences characteristic of adult MHS muscles, and thus provide suitable preparations for clinically relevant studies of MH-related cellular abnormalities. © 1996 John Wiley & Sons, Inc.     

Pathological findings in 165 patients explored for malignant hyperthermia susceptibility

The pathological findings in 165 patients explored for malignant hyperthermia (MH) susceptibility are reported. The first group of 120 subjects were patients investigated for MH. These patients had suffered an attack of MH under anaesthetic or were members of families in which a subject had died of MH. In vitro contracture tests revealed 25 malignant hyperthermia susceptible (MHS) subjects, with positive contracture tests for halothane and caffeine, 5 malignant hyperthermia subjects with reaction to caffeine only (MHC), 3 malignant hyperthermia subjects with reaction to halothane only (MHH) and 87 malignant hyperthermia negative (MHN) subjects with normal contracture tests. The second group of 45 subjects had exertional heat stroke. In vitro contracture tests performed at least 3 months after the exertional heat stroke revealed 11 MHS, 6 MHC, 2 MHH subjects and 26 MHN. In both groups, whatever the in vitro contracture test results, pathological findings were heterogeneous and revealed various changes: rhabdomyolysis, mitochondrial myopathy, denervation, type II atrophy, AMPase deficiency, non-specific findings or normal features. Central core myopathy was only observed in the first subgroup and was the only disease significantly associated with MH. In contrast to previous reports, this study demonstrates the absence of a specific malignant hyperthermia or exertional heat stroke myopathy. Furthermore, the discovery of MHS subjects among the EHS group of patients highlights the need for systematic exploration of all these patients.     

Dominantly inherited malignant hyperthermia (MH) in the King-Denborough syndrome.

A 14-year-old boy, an only child, with the phenotypical dysmorphic features of the King-Denborough Syndrome developed a severe hyperthermic episode during anesthesia which responded to the administration of sodium dantrolene. As adequate metabolic studies were not available at the time of the crisis he was referred for confirmation of the malignant hyperthermia (MH) status. Muscle tension studies confirmed the presence of MH. The patient's mother and father were subsequently tested and the mother was found to be MH positive, the father MH negative.     

Absence of malignant hyperthermia contractures in Becker-Duchenne dystrophy at age 2.

Two 2-year-old males underwent muscle biopsy that established the histopathologic diagnosis of Becker dystrophy in one, and Duchenne dystrophy in the other. Concomitant contracture testing with caffeine or halothane was normal for malignant hyperthermia (MH). The results suggest that acute hypermetabolism or acute rhabdomyolysis during anesthesia, in patients with these disorders, is related to the X-linked myopathy and its associated muscle deterioration, rather than to the autosomal dominant MH.     

Hypokalemic periodic paralysis associated with malignant hyperthermia

Hypokalemic periodic paralysis is in most cases related to mutations within the dihydropyridine receptor gene. Susceptibility to malignant hyperthermia has been linked to a different part of the same gene, but is more frequently caused by mutations within the ryanodine receptor gene. We report the association of the two disorders in a patient for whom the most frequent mutations for hypokalemic periodic paralysis were not found. This suggests further genetic heterogeneity of this condition, the interest of this case residing in the known coupling between dihydropyridine and ryanodine receptors.     

125I近距离放疗联合热疗对人胶质瘤细胞毒性的研究

目的研究125I近距离放疗联合热疗对人胶质瘤细胞的治疗效果。方法收集临床胶质瘤手术肿瘤标本进行体外细胞培养,分为热疗联合放疗组,放疗组,热疗组,空白对照组,MTT法测定各组细胞经处理后的抑制率,transwell侵袭小室测定各组细胞侵袭力变化。结果与对照组相比,各处理组的细胞抑制率显著增加,侵袭力显著降低,且随着温度的升高,热疗联合125I近距离放疗对细胞的抑制率和侵袭力影响也有显著变化。结论125I近距离放疗联合热疗对胶质瘤细胞具有一定杀伤作用。     

Caffeine sensitivity of sarcoplasmic reticulum of fast and slow fibers from normal and malignant hyperthermia human muscle

We have carried out a comparative study of caffeine sensitivity of the sarcoplasmic reticulum (SR) of fast and slow normal human fibers chemically skinned. Human slow-fiber SR is more sensitive to caffeine than fast fiber SR; however, it releases less calcium and at a lower rate than the SR of fast fibers when exposed to threshold concentrations of caffeine. These results indicate that the SR calcium release mechanisms of SR of fast and slow human fibers are homologous but not identical. An increased sensitivity of SR to caffeine is found in both fast and slow fibers from human malignant hyperthermia muscle. However, fast fibers seem to be the most affected, since their caffeine threshold for contraction is very close to that of slow fibers.     

Screening test for malignant hyperthermia in patients with persistent hyperCKemia: A pilot study

Introduction: Persistently elevated serum creatine kinase (CK) is frequently associated with predisposition to malignant hyperthermia (MH). We investigated whether a minimally invasive metabolic test is suitable to diagnose MH susceptibility among patients with hyperCKemia. Methods: Thirty‐nine participants were included: 10 were MH susceptible (MHS); 21 MH were non‐susceptible (MHN); and 8 had MHN with persistent hyperCKemia >500 U/L. Microdialysis probes were inserted into the vastus lateralis muscle, and halothane or caffeine was injected via an attached microtubing catheter. Lactate concentrations in dialysis samples were measured spectrophotometrically. Results: Baseline lactate did not differ between the groups. After local application of halothane or caffeine, a significant lactate increase was detected only in the MHS group. Conclusions: Test results were not influenced by hyperCKemia. To avoid risks and complications of a surgical muscle biopsy this microdialysis test might be a useful screening tool for MH susceptibility among patients with persistent CK elevation. Muscle Nerve 47: 677–681, 2013