[Effort-induced malignant hyperthermia. Electromyographic anomalies with a myogenic component. 10 cases]

Exertion malignant hyperthermia, usually regarded as a form of heat stroke, is mainly observed in young apparently healthy men enlisted in the army and subjected to intensive physical exertion in a warm and damp environment. It is frequently lethal. Ten cases with favourable outcome are reported. In 8 patients, EMG tracings recorded several months after the acute episode showed myogenic abnormalities. Computer-aided analysis of motor units showed a 42% reduction in mean duration of the motor unit collected from the brachial biceps and a 44% reduction of signal energy as compared with controls. Two possible reasons for these abnormalities are discussed: they may result from rhabdomyolysis or from a pre-existing muscular pathology.