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December 1974

Heat-Related Muscle Cramps

Arch Intern Med. 1974;134(6):1133. doi:10.1001/archinte.1974.00320240167028

To the Editor.  —We all owe a debt to Dr. J. P. Knochel for his masterful and comprehensive review of environmental heat illness.1 We write now in relation to one relatively minor aspect, for Dr. Knochel commented that "... muscle necrosis and myoglobinuria could conceivably follow severe episodes of heat-related muscle cramps," but "this has not been reported."We described a construction worker who had diffuse cramps after working on a hot summer day, drinking freely without replacing salt.2 Serum enzyme activity was increased and myoglobinuria was proven. There was transient azotemia and the urine contained casts, but this was attributed to the myoglobinuria; no other organs were overtly affected. Unless the renal injury is taken to mean (by definition) that, because an organ system other than the renal system was affected, this was a case of "heat exhaustion," it would seem to meet Dr. Knochel's definition of "heat