The biochemistry of malignant hyperthermia: recent concepts

Is neuroleptic malignant syndrome a neurogenic form of malignant hyperthermia?

Neuroleptic malignant syndrome is a rare and potentially lethal disorder associated with the use of antipsychotic medications. Heightened vigilance on the part of clinical providers has reduced morbidity and mortality caused by this disorder over the past decade, but there is still no consensus regarding its diagnosis, pathophysiology, or treatment. Efforts to demonstrate a direct link between neuroleptic malignant syndrome and malignant hyperthermia have been unsuccessful, indicating mutually distinct etiologies despite striking clinical similarities. This paper concisely reviews essential aspects of electromechanical transduction in muscle and nerve cells and current knowledge concerning the pathophysiology of malignant hyperthermia and neuroleptic malignant syndrome. Utilizing this conceptual framework, the author proposes that neuroleptic malignant syndrome may be caused by a spectrum of inherited defects in genes that are responsible for a variety of calcium regulatory proteins within sympathetic neurons or the higher order assemblies that regulate them. In this proposed model, neuroleptic malignant syndrome may be understood as a neurogenic form of malignant hyperthermia.

Mitochondrial anomalies in a Swiss family with autosomal dominant myoglobinuria

We report on a Swiss family in which 10 individuals of both sexes in 4 successive generations suffered from myoglobinuria, precipitated by febrile illness. It is the second family described with autosomal dominant inheritance of myoglobinuria. Four individuals suffered acute renal failure, which in two was reversible only after dialysis. In a recent case, a mitochondrial disorder was suspected because of an abnormal increase in lactate levels during an exercise test and because of a subsarcolemmal accumulation of mitochondria in a muscle biopsy, associated with a lack of cytochrome C oxidase in some muscle fibers. No mutation in the mitochondrial DNA was identified. Along with the inheritance pattern, these findings suggest that the myoglobinuria in this family is caused by a nuclear-encoded mutation affecting the respiratory chain.

The reduction of skeletal muscle lesions after experimental stress in stress-susceptible pigs protected with dantrolene

Malignant hyperthermia (MH) is a naturally occurring disease of stress-susceptible (SS) pigs subjected to triggering agents or stress. MH is characterized by accelerated muscle metabolism and hyperthermia due to abnormally increased myoplasmic Ca2+ levels. Dantrolene is used for the treatment of MH and acts by reducing the myoplasmic Ca2+ levels. Muscle lesions can be induced by experimental restraint stress in SS pigs and are suspected to be caused by increased myoplasmic Ca2+ levels. This experiment was performed in order to study if stress induced muscle lesions could be reduced by dantrolene. Nine SS pigs were exposed to experimental restraint stress provoked by a 12 min intravenous (i.v.) infusion of the depolarizing myorelaxant succinylcholine. Five pigs were orally dosed with dantrolene (5 mg/kg), twice, about 24 and 5 h before the stress (group A). The other four pigs were treated with a single i.v. infusion of dantrolene (5 mg/kg), 30 min before stress (group B). The animals were necropsied approximately 48 h after the stress and 24 skeletal muscles were examined macro- and microscopically. No clinical signs of MH occurred during the experiment. The required dose of succinylcholine was higher in group B (0.08 mg/kg/min) than in group A (0.03 mg/kg/min) indicating decreased sensitivity to succinylcholine in SS pigs after i.v. treatment with dantrolene. The pigs in group A, but not in group B showed slightly increased serum levels of creatine kinase (CK) and aspartate aminotransferase (ASAT) at time of necropsy. A significant reduction in acute muscle lesions was observed in both groups, especially in group B, when compared with SS pigs subjected to restraint stress, but not treated with dantrolene. The muscle lesions induced by the stress model are considered to be induced by increased myoplasmic Ca2+ levels since they can be reduced by dantrolene treatment.

Reduction of heart lesions after experimental restraint stress: a study in stress-susceptible pigs

Pigs, crossbreeds of Swedish Landrace and Yorkshire, about 6 months old and susceptible to develop malignant hyperthermia when exposed to halothane, were subjected to a 12-min experimental stress provoked by the myorelaxant succinylcholine. The experimental pigs were pre-treated before the stress: five were given propranolol for one week, six were given alpha-tocopherol (vitamin E) combined with selenium for 11 days, and five pigs were pre-treated with zinc (ZnSO4) for 1 month. A total of 12 untreated, stress-susceptible pigs served as controls. The blood levels of noradrenaline and adrenaline recorded during the stress were significantly reduced in the groups pre-treated with propranolol or alpha-tocopherol combined with selenium. The results show significant reduction of myocardial necrosis by beta-adrenoceptor-blocking agents and free-radical scavengers during stress-induced increased sympathetic activity.

Rhabdomyolysis: a review of the literature

Rhabdomyolysis (lysis of skeletal muscle cells) is a potentially lethal syndrome with a broad spectrum of clinical and biochemical findings. Myalgia, pigmenturia and elevated activity of serum creatine kinase are the common features. Fulminant rhabdomyolysis may be associated with severe metabolic disturbances and involvement of other organ systems. Cardiac arrest, compartment syndrome and acute renal failure are the major complications. The extent of the life-threatening complications of rhabdomyolysis strongly depends on early diagnosis and adequate therapy. As the repair mechanism of striated muscle functions very well, the prognosis of adequately treated rhabdomyolysis is excellent. This article reviews the present state of knowledge of clinical and biochemical diagnosis of rhabdomyolysis, the pathophysiologic background, the classification and the etiological provocative factors.

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.