Malignant hyperthermia

Functional characterization of RYR1 variants identified in malignant hyperthermia susceptible individuals

Malignant hyperthermia is a pharmacogenetic disorder triggered by halogenated anesthetic agents in genetically predisposed individuals. Approximately 70 % of these individuals carry mutations in RYR1, the gene encoding the ryanodine receptor calcium channel of skeletal muscle. In this study, we performed functional analysis of 5 RYR1 variants identified in members from 8 families who had been diagnosed by the IVCT. Of the 68 individuals enrolled in the study, 43 were diagnosed as MHS, 23 as MHN, and 2 individuals were not tested. Here we demonstrate that the 5 RyR1 variants cause hypersensitivity to RyR1 agonist-mediated calcium release. According to the EMHG scoring matrix these five genetic variants can be classified as follows: c.8638G>A (p.E2880K) and c.11314C>T (p.R3772W) likely pathogenic, c.11416G>A (p.G3806R), c.14627A>G (p.K4876R) and c.14813T>C (p.I4938T), pathogenic (RefSeq NM_000540.3). We propose that the newly functionally characterized RYR1 variants, be included in the panel of variants to be used for the molecular diagnosis of MHS.

Drug-induced hyperthermia

Drug-related causes of hyperthermia can often be overlooked in the setting of elevated body temperature. This article reviews the pathophysiology, presentation, and treatment of several drug-induced hyperthermia syndromes: malignant hyperthermia, neuroleptic malignant syndrome, sympathomimetic poisoning, and anticholinergic toxicity. Although the general approach is similar, specific management strategies may be required for each syndrome.

Effects of dantrolene on cooling times and cardiovascular parameters in an immature porcine model of heatstroke

OBJECTIVE

To evaluate the effects of dantrolene on cooling times and cardiovascular parameters in an immature porcine model of heatstroke.

DESIGN

Prospective, randomized, controlled, multigroup study.

SETTING

Research animal laboratory.

SUBJECTS

Yorkshire piglets (n = 16), 4 to 5 wks of age, 3.5 to 4.5 kg of body weight.

INTERVENTIONS

Animals were slowly heated with a radiant heat source to 43 degrees C and then maintained at this temperature for 30 mins. The animals were then removed from the heat source and randomized into one of four groups to receive either conventional cooling methods consisting of fluid resuscitation with 0.9% sodium chloride solution, sponging with room temperature water, mechanical fanning, and gastric lavage with iced 0.9% sodium chloride solution (group 1), conventional cooling methods and dantrolene (group 2), conventional cooling methods and dantrolene's vehicle mannitol (group 3), or no treatment (group 4). Cooling times, defined as the time required to reach a core body temperature of 38.5 degrees C, and cardiovascular parameters for each group were then compared.

MEASUREMENTS AND MAIN RESULTS

Animals in groups 1, 2, and 3 had significantly (p < .05) lower core body temperatures than animals that received no treatment at the conclusion of the experiment. Piglets in groups 2 and 3 had faster cooling times than piglets in group 1 (p < .05). However, there was no statistically significant difference in cooling times between the animals in groups 2 and 3. There were no statistically significant differences in heart rate, mean arterial pressure, central venous pressure, pulmonary artery occlusion pressure, or systemic vascular resistance index between animals in groups 1, 2, or 3. Group 3 piglets had higher cardiac indices and stroke indices than the piglets in the other groups (p < .05).

CONCLUSIONS

Therapeutic interventions with conventional cooling or conventional cooling and dantrolene provided significant improvement in cardiovascular function in an immature porcine heatstroke model. Dantrolene, given with conventional cooling methods, offered no significant improvement in cardiovascular parameters compared with conventional cooling methods alone. Dantrolene significantly shortened the cooling time compared with conventional cooling but did not significantly shorten the cooling time compared with its vehicle, mannitol. Although dantrolene significantly shortened the cooling time, it did not appear to be superior compared with conventional cooling methods in treating heatstroke in this immature porcine heatstroke model.

Malignant hyperpyrexia in oral surgery--case report and literature review

A case of malignant hyperpyrexia (MH) occurring in a patient undergoing orthognathic surgery is reported which resulted in the procedure being abandoned prior to completion. The oral surgeon's role in recognising the early clinical signs of masseteric spasm and central cyanosis is highlighted. The case shows that with proper investigation and management the MH susceptible patient was able to have a second anaesthetic with safety to complete the surgery.

Free radicals and calcium homeostasis: relevance to malignant hyperthermia?

The regulation of intracellular free calcium ions (Ca2+) in skeletal muscle at rest and during contraction depends on mechanisms such as Na(+)-Ca2+ exchangers, Ca(2+)-ATPases, and the voltage-sensitive ryanodine receptor. The susceptibility of these regulatory mechanisms to free-radical-mediated damage may be increased because of their location within the lipid membranes of sarcolemma, sarcoplasmic reticulum, and mitochondrion with resultant uncontrolled increases in myoplasmic Ca2+ concentration and cell death. The potentially fatal pharmacogenetic disorder, malignant hyperthermia (MH), is characterised by muscle rigidity, arrhythmias, lactic acidosis, and a rapid rise in body temperature. The sequence of events responsible for the MH syndrome remains uncertain, but it has been variously ascribed to faults in many of the Ca2+ regulatory mechanisms. In swine the condition is associated with a specific mutation in the ryanodine receptor, whereas in humans the syndrome is genetically heterogenous. Free-radical-mediated peroxidation of membrane lipids and proteins also results in the rapid efflux of Ca2+ from organelles, and the detection of products of free radical reactions in tissue from MH-susceptible individuals using electron spin resonance spectroscopy provides evidence for the involvement of free radicals in the MH syndrome.

Rhabdomyolysis in childhood. A primer on normal muscle function and selected metabolic myopathies characterized by disordered energy production

Patients with rhabdomyolysis present an important clinical problem. In acute episodes immediate treatment may be necessary to prevent significant morbidity and mortality. Evaluation of affected patients necessitates an understanding of basic muscle pathophysiology and of the variety of disturbances that can interfere with muscle energy metabolism. The physician must then pursue a systematic stepwise evaluation (Table 6) that includes obtaining relevant history and laboratory studies, as well as arranging for appropriate provocative testing and muscle biopsy. Once the diagnosis is established, patient and family counseling is necessary, particularly in genetic disorders. Unfortunately, specific therapies have not proven entirely successful, and treatment generally has been directed at reducing the severity of rhabdomyolytic episodes.

Malignant hyperthermia. Quick recognition and treatment to avoid death

Malignant hyperthermia, a disorder of uncertain genetic transmission related to use of certain anesthetics and muscle relaxants, is uncommon and potentially fatal. It has been most commonly linked to succinylcholine chloride (Anectine, Quelicin, Sucostrin) and halothane (Fluothane). The most important treatment method, after discontinuation of the triggering agent(s), is immediate administration of dantrolene sodium (Dantrium). Diagnostic testing of susceptibility is available but has significant limitations. If the new phosphorus nuclear magnetic resonance spectroscopy proves to be an accurate test for susceptibility and becomes more readily available, decreases in the current case-fatality rate of 10% may follow.

Delayed sudden death after ingestion of MCPP and ioxynil: an unusual presentation of hormonal weedkiller intoxication

A patient who died in asystole less than 18 h after ingestion of 'Clovercide Extra', a combination hormonal weedkiller containing ioxynil and 4-chloro-2-methyl phenoxypropionic acid, is described. Previous reports describe coma as an early event following ingestion of these herbicides. In contrast our patient, although showing other characteristic features, including metabolic acidosis, tachycardia, pupillary constriction and pyrexia, remained conscious until the terminal event. Absence of coma does not appear to be related to a more favourable outcome.