Maximal exercise and muscle energy metabolism after recovery from exercise hyperthermia syndrome

Comparison of Transcriptomic Changes in Survivors of Exertional Heat Illness with Malignant Hyperthermia Susceptible Patients

Exertional heat illness (EHI) is an occupational health hazard for athletes and military personnel-characterised by the inability to thermoregulate during exercise. The ability to thermoregulate can be studied using a standardised heat tolerance test (HTT) developed by The Institute of Naval Medicine. In this study, we investigated whole blood gene expression (at baseline, 2 h post-HTT and 24 h post-HTT) in male subjects with either a history of EHI or known susceptibility to malignant hyperthermia (MHS): a pharmacogenetic condition with similar clinical phenotype. Compared to healthy controls at baseline, 291 genes were differentially expressed in the EHI cohort, with functional enrichment in inflammatory response genes (up to a four-fold increase). In contrast, the MHS cohort featured 1019 differentially expressed genes with significant down-regulation of genes associated with oxidative phosphorylation (OXPHOS). A number of differentially expressed genes in the inflammation and OXPHOS pathways overlapped between the EHI and MHS subjects, indicating a common underlying pathophysiology. Transcriptome profiles between subjects who passed and failed the HTT (based on whether they achieved a plateau in core temperature or not, respectively) were not discernable at baseline, and HTT was shown to elevate inflammatory response gene expression across all clinical phenotypes.

Exertional Heat Stroke and Susceptibility to Malignant Hyperthermia in an Athlete: Evidence for a Link?

OBJECTIVE

To describe the possible association (pathophysiologic and clinical features) between exertional heat stroke (EHS) and malignant hyperthermia (MH).

BACKGROUND

Both EHS and MH are acute and life-threatening disorders. It has repeatedly been shown that EHS can occur in well-trained patients with known MH-associated mutation in the RYR1 gene in the absence of any extreme environmental conditions or extreme physical activity, thereby supporting a possible link between EHS and MH. In this case, a highly trained 30-year-old male athlete suddenly collapsed while running. He had initial hyperthermia (40.2°C) and progressive multiple organ failure requiring medical management in an intensive care unit. After he recovered completely, a maximal exercise test was performed and showed an obvious abnormality of oxidative metabolism in muscle; genetic analysis of the RYR1 gene identified a heterozygous missense variation p.K1393R. Consequently, the athlete was given appropriate information and allowed to progressively return to sport competition.

DIFFERENTIAL DIAGNOSIS

Doping, use of drugs and toxic agents, exercise-associated hyponatremia, exertional heat illness.

TREATMENT

Initial management started with the basic resuscitative guidelines of airway, breathing, and circulation (intubation). Cooling, administration of fresh frozen plasma, and intensive rehydration resulted in improvement.

UNIQUENESS

To our knowledge, ours is the first description of this MH mutation (p.K1393R) in the RYR1 gene that was associated with exertional rhabdomyolysis involving a dramatic impairment of oxidative metabolism in muscle.

CONCLUSIONS

Common features are shared by EHS and MH. Careful attention must therefore be paid to athletes who experience EHS, especially in temperate climates or when there are no other predisposing factors.

Malignant hyperthermia and myotonic disorders

Advances in physiology and molecular genetics have promoted greater understanding of the various clinical manifestations of muscle disorders. For example, myotonia or profound weakness may be observed in sodium channel disease (e.g., paramyotonia congenita or hyperkalemic periodic paralysis), depending on the specific channel defect or with slight changes in membrane potential. Observed effects of anesthetic techniques have been essential to elucidating the primary muscular nature of myotonia. Commonly used anesthetic medications have potentially lethal (e.g., MH) or serious (e.g., myotonic dystrophy) adverse effects. Conversely, lidocaine or propofol may have therapeutic benefit for patients with skeletal muscle sodium channel disorders. Additional investigation is required to improve our understanding of how age, gender, or other factors determine the phenotypic expression of malignant hyperthermia. Future research holds the promise for more accurate pre-anesthetic identification of persons with heritable myopathies, especially those who are asymptomatic. Enhanced awareness of multiple organ system involvement in myotonic dystrophy is essential for planning perioperative care. Patients with periodic paralysis require that we know factors that incite or inhibit the development of their attacks. Advances in bench research and detailed clinical studies will further improve our ability to provide optimal care for patients with muscle disorders.