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The genetic basis of malignant hyperthermia.

Anaesthesia can induce skeletal muscle rigidity, hypermetabolism and high fever in humans genetically predisposed to malignant hyperthermia. If not immediately reversed, such episodes can lead to tissue damage and death. In swine with the corresponding condition, stress can induce death or lead to devalued meat products. Since muscle contraction is controlled by sarcoplasmic Ca2+, the abnormality, as reviewed here by David H. MacLennan, could reside in the skeletal muscle Ca(2+)-release channel gene, RYR1. Several observations support the view that a single RYR1 mutation is causal of malignant hyperthermia in all breeds of pigs and in at least some human families: the substitution of Cys for Arg615 as the sole deduced amino acid sequence change in a comparison of malignant hyperthermia and normal porcine RYR1 cDNAs; the linkage of this mutation to malignant hyperthermia in over 450 pigs in six breeds, including 338 meioses; and the appearance of the corresponding mutation, Cys for Arg614, across a species barrier, in a few human families, where it also cosegregates with malignant hyperthermia. Linkage of malignant hyperthermia to RYR1 is, however, not observed in all human families with malignant hyperthermia. Accordingly, other abnormal genes that may cause the condition are being sought.

Anesthesia↗

Halothane and temperature interact to increase succinylcholine-induced jaw contracture in the rat.

BACKGROUND: The agonist actions of succinylcholine (SCh) have recently come under study because of their involvement in the clinical problem of masseter muscle rigidity, and their possible involvement in malignant hyperthermia. The authors investigated factors affecting SCh-induced contractures in an animal preparation. METHODS: Rats were anesthetized with either halothane (1-2%) or pentobarbital. Resting and twitch isometric tension were measured from the jaw muscles. Succinylcholine (500 or 750 micrograms/kg) was administered intravenously, producing increases in resting tension (i.e., contractures). Jaw muscle temperature was controlled by radiant heat. RESULTS: Succinylcholine increased jaw muscle tension for several seconds. These contractures exhibited tachyphylaxis, and were antagonized by vecuronium (0.8-1.5 mg/kg), indicating mediation by acetylcholine receptors (AChR). In the presence of 2% halothane, contractures were tenfold greater at a rectal temperature of 41 degrees C than at 37 degrees C. In contrast, under 50 mg/kg intraperitoneal pentobarbital anesthesia, contractures were not affected by rectal temperature. Neither the half-decay time of contracture nor twitch tension (0.2 Hz, preceding SCh) were increased in the presence of halothane at 41 degrees C. In a set of experiments in which rectal temperature was maintained at 37 degrees C but jaw temperature was varied between 36-41 degrees C, there was a significant regression of SCh-induced jaw contracture on temperature in the presence of halothane. In contrast, there was no significant relationship between jaw temperature and contracture in the presence of pentobarbital. CONCLUSIONS: These results in the rat demonstrate a temperature-dependent interaction between halothane and SCh that has not previously been described.

Animals↗

Muscle strength testing in Parkinson's disease.

Isotonic muscle strength measured by a quantitative technique was decreased in early Parkinson's disease compared to age-matched controls. Weakness was present both on the affected and unaffected side in hemiparkinsonism. Similar degrees of weakness occurred in limbs with tremor or rigidity. Muscle weakness appears to be a primary symptom of Parkinson's disease which may relate to disturbed motor programming due to basal ganglia dysfunction.

Arm↗

Ca-induced Ca release in malignant hyperthermia-susceptible pig skeletal muscle.

To provide information regarding the cause of the muscle rigidity in malignant hyperthermia-susceptible (MHS) pigs, the Ca-induced Ca-release mechanism of the sarcoplasmic reticulum (SR), the Ca uptake by the SR, and the Ca-activated tension production of the contractile system were examined in skinned skeletal muscle fibers from MHS and normal pigs. In muscles of MHS pigs, the rate of Ca-induced Ca release was significantly higher than in normal muscle. The potentiation effect on Ca-induced Ca release by halothane and caffeine did not differ appreciably between MHS and normal fibers. The rate of Ca uptake by the SR and the Ca sensitivity of the contractile system of MHS fibers were not different from those of normal fibers, and halothane in an anesthetic concentration exerted no effect on them. Dantrolene inhibited the Ca-induced Ca release at 38 degrees C. These results suggest that the principal cause of malignant hyperthermia (MH) in MHS pigs is due to the enhancement of the Ca-induced Ca-release mechanism of the SR of the skeletal muscle.

Adenosine Triphosphate↗

Phenotypes associated with malignant hyperthermia susceptibility in swine genotyped as homozygous or heterozygous for the ryanodine receptor mutation.

We have examined the phenotypic expression of several parameters associated with malignant hyperthermia (MH) susceptibility in three groups (homozygous normal, homozygous abnormal and heterozygous) of Yorkshire/Duroc swine genotyped by a mutation in the ryanodine receptor. Subgroups of homozygous abnormals were classified further by the appearance or absence of muscle rigidity on prolonged in vivo challenge with halothane and suxamethonium. Four swine heterozygous for the proposed MH mutation were indistinguishable from five homozygous normal swine in temperature, heart rate, lactate concentrations, base excess and pH determined during the prolonged halothane and suxamethonium challenge. Resting creatine kinase concentrations, the in vivo barnyard challenge, the in vitro contracture response of skeletal muscle to 3% halothane and the threshold for Ca(2+)-induced Ca2+ release were also similar for subgroups of homozygous normals and heterozygotes. Therefore, inheritance of only one allele carrying the defect in the ryanodine receptor does not significantly alter phenotypes associated with MH susceptibility in this strain of swine. As four swine homozygous for the proposed MH defect did not exhibit rigidity and three of these had no other signs of MH on prolonged halothane and suxamethonium challenge, we conclude that the reported mutation in the ryanodine receptor may be necessary, but is not sufficient, for consistently eliciting the malignant hyperthermia syndrome. These findings suggest that a modulator of the syndrome may explain variability within individuals in human MH.

Animals↗

Neuroleptic malignant syndrome induced by domperidone.

A 47-year-old woman with diabetic gastroparesis, on treatment with domperidone, a dopamine-receptor antagonist, was admitted to the hospital in coma, with high blood pressure and nonreactive pupils. She then developed high fever. Her condition progressively worsened for two days, when muscle rigidity was noted and creatine phosphokinase was greater than 2000 U/liter. A diagnosis of neuroleptic malignant syndrome was made, and the patient was given dantrolene with prompt and complete resolution of all signs and symptoms. Subsequent inquiry revealed a distant past history of positive muscle biopsy for malignant hyperthermia, obtained after the diagnosis had been made in a family member. This case suggests that domperidone may induce neuroleptic malignant syndrome and that patients with malignant hyperthermia are at increased risk for this complication.

Dantrolene↗

Changes in muscle tone are regulated by D1 and D2 dopamine receptors in the ventral striatum and D1 receptors in the substantia nigra.

Muscle rigidity associated with antipsychotic drug treatment is believed to result from reduced striatal dopamine neurotransmission. In the current study the regulatory roles of dopamine D1 and D2 receptor subfamilies in the dorsal (DSTR) and ventral striatum (VSTR) and substantia nigra (SN) were investigated on muscle tone, assessed as increases in tonic electromyographic (EMG) activity. Rats were injected with the irreversible D1/D2 antagonist N-ethoxycarbonyl-2-ethoxy, -1,2-dihydroquinoline (EEDQ), the reversible D1 antagonist SCH23390, or D2 antagonist sulpiride. Increased EMG activity was observed following injection of EEDQ and SCH23390 into the SN or VSTR, and sulpiride into the VSTR. Mapping, using quantitative autoradiographic analysis of dopamine receptor occupancy after striatal injections, showed D1 and D2 receptors in discrete ventral sites were associated with EMG increases. Overall the results support roles for dopamine D1 and D2 receptors in the ventral striatum, and D1 receptors in the substantia nigra, in the regulation of muscle tone.

Animals↗

The genetic basis of malignant hyperthermia.

Malignant hyperthermia (MH) susceptibility remains the commonest cause of death owing to general anaesthesia. In humans, genetically predisposed to MH, anaesthesia can induce skeletal muscle rigidity, hypermetabolism and hyperthermia, which if not immediately reversed can lead to tissue injury and death. In swine, the corresponding condition leads to stress-induced deaths and devalued meat products. Aberrant behaviour in the calcium (Ca2+) release channel (the ryanodine receptor) of skeletal muscle sarcoplasmic reticulum has been implicated in the cause of both the porcine and human syndromes by biochemical, physiological and molecular genetic analysis. In swine, a single mutation in the ryanodine receptor gene (RYR1) can account for all cases of MH in all breeds, but a series of different RYR1 mutation are uncovered in human families with MH. In addition, the lack of linkage between MH and RYR1 in some families indicates a heterogeneous genetic basis for the human MH.

Animals↗

Halothane sensitivity of young pigs in vivo and in vitro.

Piglets less than 8 wk of age that are known by genotype to be malignant hyperthermia-susceptible (MHS) do not usually develop characteristic hyperthermia and limb muscle rigidity in response to a brief halothane exposure (5 min of 3%). To determine whether a malignant hyperthermia (MH) episode could nevertheless be provoked by a more rigorous challenge, both genetically MHS (Pietrain) and normal (Yorkshire) 5-wk-old piglets were exposed to a combined halothane-succinylcholine challenge. Only two of eight MHS piglets developed limb rigidity; however, all MHS piglets (and no normal piglets) developed clinical signs of MH episode initiation during the 30-min challenge. Temperatures rose from 37.4 to 38.6 degrees C in MHS piglets while falling slightly in normal piglets. In MHS piglets, venous pH fell from 7.46 +/- 0.02 to 6.88 +/- 0.07, PVCO2 rose from 36 +/- 2 to 126 +/- 17 mmHg, and plasma concentration of K+ rose from 4.0 +/- 0.1 to 7.1 +/- 0.6 mM, whereas all values remained stable in normal piglets. Muscles removed from the same piglets before the halothane-succinylcholine challenge were exposed to halothane in vitro. The muscles from genetically MHS piglets responded to halothane with characteristic depression of tetanic tension and prolonged tetanus relaxation time but did not develop halothane-induced contractures. We conclude that, in the absence of either halothane-induced limb rigidity or in vitro contractures, these young animals were still susceptible to potentially fatal MH episodes on exposure to appropriate triggering agents. The MH defect is apparently partially masked in piglets and expressed fully only in older pigs.

Animals↗

Succinylcholine infusion associated with hyperthermia in ponies anesthetized with halothane.

Succinylcholine was administered by infusion to halothane-anesthetized ponies to determine dosage requirements for surgical relaxation up to 3 hours' duration. This was not possible to do, since 4 of 6 ponies studied developed severe reactions characterized by prolonged muscle fasciculations after the initial succinylcholine dose, muscle rigidity, hyperthermia, hypercapnia, tachycardia, increasing pulse pressure, and metabolic acidosis. The reactions resembled those associated with malignant hyperthermia, a disease recognized in persons and swine. Two ponies showed signs of the phase II or desensitization block of succinylcholine. All ponies recovered from anesthesia without signs of muscle injury.

Acidosis↗

Long-term treatment with abecarnil does not induce diazepam-like dependence in mice.

Abecarnil (isopropyl-6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a metabolically stable anxiolytic and anticonvulsant beta-carboline derivative with few sedative and muscle relaxant effects in rodents. Abecamil binds with high affinity to benzodiazepine receptors. Because long-term treatment with benzodiazepines leads to development of dependence, we evaluated in mice whether abecarnil also possesses a potential for producing dependence, using electroencephalographic and electromyographic monitoring, and behavioral assessment of anxiety to detect withdrawal responses after chronic treatment. Diazepam was used as a reference. Mice withdrawn from chronic treatment with diazepam (15 mg/kg/day for 12 days) showed a time-related evolution of anxiety, muscle rigidity and seizures between days 4 and 21 after discontinuation of the treatment. A period between withdrawal days 1 and 3 was symptom free. Mice withdrawn from chronic administration of abecarnil (6 mg/kg/day for 12 days) showed no anxiety and no changes in seizure susceptibility and muscle tone. The doses of diazepam and abecarnil used for chronic treatment were equivalent in terms of kinetics and binding to benzodiazepine receptors. These data indicate that long-term treatment with abecarnil does not induce benzodiazepine-like dependence in mice. Thus, it may be predicted that chronic treatment with abecarnil in humans may offer an important alternative to benzodiazepines in the treatment of anxiety.

Animals↗

Further studies of porcine malignant hyperthermia.

A non-lethal procedure for identifying pigs apt to develop malignant hyperthermia is described. Susceptible animals were exposed to a variety of anaesthetic and other agents and it was shown that thiopentone sodium and CT 1341 (Glaxo) afforded a measure of protection against the development of the syndrome. Pretreatment with procaine did not prevent the onset of the condition and the administration of procaine when muscle rigidity was present failed to prevent a fatal outcome. The syndrome was induced in susceptible animals by halothane, chloroform, and a combination of halothane with suxamethonium. The effects of cyclopropane in susceptible pigs could not be predicted, and other tests showed that suxamethonium alone would not induce muscle contracture. Pretreatment with lignocaine failed to prevent induction of the syndrome by halothane.We believe that the porcine syndrome may result from more than one defect and that in one particular type the most effective treatment is immediate cooling coupled with the administration of sodium bicarbonate.

Acidosis↗

[Delayed onset malignant hyperthermia after a closure of ventricular septal defect].

An 18 month-old girl was diagnosed as ventricular septal defect (VSD) with mild aortic valve prolapse. She underwent a closure of VSD. Intra-and early postoperative course was uneventful. However, 20 hours after surgery, sudden bradycardia led to cardiac arrest and strong muscle rigidity was seen. Hyperkalemia and metabolic acidosis rapidly progressed and resuscitation was failed. Extracorporeal life support and continuous hemodialysis were initiated, but the patient died with multiple organ failure on 5th postoperative day. Her clinical course supported the diagnosis of delayed onset malignant hyperthermia. Histopathological findings of muscle biopsy were consistent with rhabdomyolysis, and immunopathological stains demonstrated changes as in a Duchenne type muscular dystrophy carrier. Delayed onset malignant hyperthermia is an extremely rare complication of general anesthesia. We should be aware of this lethal condition, which occurs with a certain time lag after surgery, especially when the patient has possible background of myopathy.

Female↗

[Serotonin syndrome. Several cases of this often overlooked diagnosis].

During the recent decade an increasing number of inquiries concerning cases of overdoses exhibiting typical signs of the serotonin syndrome have been recorded at the Swedish Poisons Information Centre. Four of these cases are presented together with a review of the literature. All patients had overdosed moclobemide and in one case this was the only drug taken. The other patients had ingested moclobemide together with citalopram (2 cases) and clomipramine (1 case). Moreover, other serotoninergic pharmaceuticals as sertraline and sumatriptan were simultaneously ingested in one case and buspirone in another. Three of the cases had hyperthermia, > 40 degrees C and the same number showed pronounced muscle rigidity, coma and mydriasis. Other severe signs and symptoms upon admission included positive Babinski and trismus in two cases each and seizures in one. All patients received mechanical ventilation. Two were treated with dantrolene sodium and one of them was given cyproheptadine as well. One patient received cyproheptadine treatment alone and another prolonged muscle relaxation. Three patients had a typical short clinical course, whereas one patient developed rhabdomyolysis, DIC and arrhythmias. All patients fully recovered.

Adult↗

[Serotonin syndrome--several cases of this often overlooked diagnosis].

During the recent decade an increasing number of inquiries concerning cases of overdoses exhibiting typical signs of the serotonin syndrome have been recorded at the Swedish Poisons Information Centre. Four of these cases are presented together with a review of the literature. All patients had overdosed moclobemide and in one case this was the only drug taken. The other patients had ingested moclobemide together with citalopram (2 cases) and clomipramine (1 case). Moreover, other serotoninergic pharmaceuticals as sertraline and sumatriptan were simultaneously ingested in one case and buspirone in another. Three of the cases had hyperthermia, > 40 degrees C and the same number showed pronounced muscle rigidity, coma and mydriasis. Other severe signs and symptoms upon admission included positive Babinski and trismus in two cases each and seizures in one. All patients received mechanical ventilation. Two were treated with dantrolene sodium and one of them was given cyproheptadine as well. One patient received cyproheptadine treatment alone and another prolonged muscle relaxation. Three patients had a typical short clinical course, whereas one patient developed rhabdomyolysis, DIC and arrhythmias. All patients fully recovered.

Adult↗

Succinylcholine metabolite succinic acid alters steady state activation in muscle sodium channels.

BACKGROUND: Animal experiments revealed that succinylcholine produced masseter muscle rigidity and activated myotonic discharges despite neuromuscular blockade with a nondepolarizing blocker. These results suggest that either succinylcholine or its metabolites might interfere directly with voltage-operated ion channels of the sarcolemma. The aim of this study was to examine effects of one product of succinylcholine hydrolysis, succinic acid, on voltage-gated muscle sodium (Na+) channels. METHODS: Alpha subunits of human muscle sodium channels were heterologously expressed in HEK293 cells. Activation of Na+ currents was examined applying standard whole-cell voltage-clamp protocols in the absence (control and washout) and presence of succinic acid in different concentrations (0.05-10 mm). RESULTS: Succinic acid shifted the midpoints of steady state activation plots in the direction of more negative test potentials, indicating that channels open during smaller depolarizations in the presence of the drug. The maximum amount of the negative shift in 10 mm succinic acid was -6.3 +/- 1.7 mV; the EC50 for this effect was 0.39 mm. In addition, succinic acid (10 mm) significantly enhanced maximum currents after depolarizations with respect to a series of control experiments. CONCLUSION: Succinic acid facilitates voltage-dependent activation in muscle sodium channels in vitro. This might lead to muscle hyperexcitability in vivo.

Anti-Ulcer Agents↗

An update on the malignant hyperthermia syndrome.

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle. In humans, MH is inherited in an autosomal dominant fashion; in swine, the principal model for MH, it is in a recessive fashion. Those with MH susceptibility usually are asymptomatic except in the presence of certain "triggering" anaesthetic agents such as isoflurane, enflurane and the muscle relaxant succinylcholine. Upon such exposure hypermetabolism, increased CO2 production, acidosis, muscle rigidity, rhabdomyolysis and hyperthermia occur. Untreated, death may result in 70% of patients. With prompt diagnosis and treatment with dantrolene sodium, the mortality is less than 10%. The overall incidence of MH is low (perhaps 1:50,000 anaesthetics), but it is more common in children. Children also display a paradoxical increase in jaw muscle tone to succinylcholine which often presages MH, but confusing clinically, may also be a normal response to succinylcholine. The pathophysiology of MH centres around a defect in calcium flux in skeletal muscle. A specific base pair change in the gene that codes for the ryanodine receptor calcium channel in muscle has been demonstrated in susceptible swine, but occurs rarely in humans. It is hoped that the understanding of the molecular genetics of MH will lead to a simpler diagnostic test than is currently available, and enhance our understanding of MH and its relation to other myopathies.

Anesthetics↗

[A case of posttraumatic parkinsonism].

We report a case of a 52-year-old man with posttraumatic parkinsonism. He was admitted to our department because of right-sided hand tremor and gait disturbance. He had suffered from a severe head injury incurred in a traffic accident with brief unconsciousness 6 months before admission. Three weeks after his injury, tremor and rigidity in the right upper limb developed, and he walked dragging his right leg. Five months after his injury, he received 1-dopa therapy, exhibiting a moderate improvement in parkinsonian symptoms. On admission, he was demented to a mild degree with masked face and monotonous speech. He presented with resting-postural-kinetic tremor and muscle rigidity on the right side. Cranial CT and MRI showed no abnormality. Inter-peak latencies of waves III to V of BAEP were significantly longer in this patient than in normal subjects. This BAEP findings suggested an upper brainstem lesion. 123I-IMP SPECT disclosed decreased cerebral blood flow in the left thalamus, bilateral frontal and parietal cortices. We diagnosed this case as having posttraumatic parkinsonism. Parkinsonism in the present case may be due to the involvement of multiple neuronal circuits of the extrapyramidal system at the level of the midbrain to the thalamus.

Amphetamines↗