Résumé :
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Exertional heat stroke (EHS) occurs in young, healthy individuals engaged in a strenuous physical activity and is accompanied by hyperthermic and lost of consciousness. Given that EHS and Malignant Hyperthermia (MH), a subclinical myopathy due to abnormal calcium handling, share a few clinical features, one could wonder whether calcium handling and muscle energetics are altered in EHS patients as it is the case in MH susceptible subjects (1). In the present study, we have analyzed the results of 182 subjects included in a survey of military personnel who have had EHS between 2004 and 2006. Each subject was included in the study after informed written consent was obtained. A muscle biopsy was excised from the biceps muscle and divided into three samples. A histological analysis was performed on the first sample while the second sample was used for in vitro contracture tests (IVCT) (4). Genetic analysis of the third sample was performed in order to check the existence of mutations commonly found in MHS subjects (2). Muscle energetics was analyzed non invasively during a standardized rest-exercise-recovery protocol using 31P magnetic resonance spectroscopy (MRS) as previously described (3). According to the IVCT, 14.4 % of the subjects were classified as MHS (i.e. both halothane and caffeine tests were abnormal) and 15.6% were equivocal for Halothane (i.e. the halothane but not the caffeine test was abnormal). IVCT with caffeine were abnormal in 20% of the subjects so that overall half of the subjects displayed IVCT abnormalities. Histological analyses did not reveal significant alterations whereas the non invasive investigation of muscle energetics, assessed with MRS, was abnormal for 25% of the subjects. Among the subjects with abnormal IVCT, 24% displayed metabolic abnormalities during the standardized exercise test. The preliminary genetic investigations performed in 8 subjects did not show mutations in the RYR1 gene. Overall, 60% of the subjects investigated displayed infraclinical abnormalities after an EHS episode. Although we did not find typical histological or metabolic abnormalities but rather heterogeneous alterations, subjects with EHS must be investigated through a multidisciplinary approach in order to better understand the metabolic and genetic bases, if any, of EHS. 1. Bendahan D. et al. Anesthesiology 88: 96-107, 1998. 2. Monnier N and Lunardi J.. Ann Biol Clin (Paris) 58: 147-156, 2000. 3. Bendahan D et al.. Anesth Analg 93: 683-689, 2001. 4. Bendahan D. Acta Anaesthesiol Scand 48: 1019-1027, 2004.
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