A noninvasive investigation of muscle energetics supports similarities between exertional heat stroke and malignant hyperthermia

Exertional heat stroke (EHS) is usually triggered by strenuous exercise per formed under hot and humid environmental conditions. Although the pathogene sis of an EHS episode differs from that of a clinical malignant hyperthermi a (MH) crisis, both conditions share some similarities in symptoms, such as the abnormal increase in core temperature. By use of P-31 magnetic resonan ce spectroscopy, we analyzed the muscle energetics of 26 post-EHS subjects for whom in vitro halothane/caffeine contracture tests were abnormal and in vestigated possible similarities with subjects susceptible to MH. An early decrease of pH was noted during the first minute of exercise in EHS subject s as compared with controls. EHS subjects were divided into two subgroups a ccording to the diagnostic score previously developed for MH subjects. The 19 subjects (73%) with a score higher than 2 displayed significantly larger caffeine-induced and earlier ryanodine-induced contractures on muscle biop sies as compared with the rest of the group (7 subjects). The results demon strate that muscle energetics are abnormal in subjects who have experienced EHS and suggest a possible link between MH and EH, although all EHS cannot be considered as MH.