Elevated CK-MB Levels in Marathon Runners

Abstract

To the Editor.— Siegel et al have demonstrated marked elevations of serum levels of creatine kinase MB (CK-MB) isoenzyme (up to 21 times the upper limit of normal) in marathon runners during the postrace period (1981;246:2049). They believed that the source of this isoenzyme in their subjects was skeletal muscle injury. Largely on the basis of negative technetium Tc 99m pyprophosphate scintigrams, they concluded that serum CK-MB in these runners does not arise from a myocardial source. While skeletal rhabdomyolysis does appear to be the principal source of CK-MB, another lesion that should be considered in this setting is ischemic injury to individual myocardial fibers; such injury may cause substantial leakage of CK-MB isoenzyme and may be reversible or irreversible (cardiac myocytolysis). Cardiac myocytolysis may be defined as disintegration of individual myocardial fibers unaccompanied by an inflammatory response. Ischemia resulting in myocytolysis may involve randomly distributed myocardial fibers during a