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.
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