MYOSIN HEAVY-CHAIN FRAGMENTS AND CARDIAC TROPONINS IN THE SERUM IN RHABDOMYOLYSIS - DIAGNOSTIC SPECIFICITY OF NEW BIOCHEMICAL MAKERS

Background: Myosin is the major structural protein in muscle. Antibodi es to beta-type heavy meromyosin react with cardiac and slow-twitch sk eletal muscle. Cardiac TnT and TnI were developed as tissue-specific i ndicators. Objectives: To study myosin heavy-chain fragments as a dela yed marker of previous rhabdomyolysis. To examine the cardiac specific ity of cardiac troponin T (TnT) and cardiac troponin I (TnI) in patien ts with severe skeletal muscle damage. Design and Methods: Serum myosi n heavy-chain fragments, TnT, and TnI were studied up to 12 days after diagnosis in relationship to the serum creatine kinase level in 20 pa tients with rhabdomyolysis. The mean peak serum creatine kinase activi ty was 91 300 U/L. Myosin heavy-chain fragments were measured by an im munoradiometric assay, TnT by a one-step immunoenzymometric assay, and TnI by an immunoenzymometric assay. Results: Values for serum myosin heavy-chain fragments were greater than the upper limit of normal in a ll patients. The peak value (70 times the upper normal limit, on avera ge) was usually achieved 4 to 7 days after the diagnosis of rhabdomyol ysis, and it was increased up to 12 days. The peak level of TnT was in creased in 95% of the patients, and it correlated strongly with the pe ak activity of serum creatine kinase. The highest TnI value was above the detection limit of myocardial infarction in 30% of the patients. H alf of these patients were the only patients with ischemic changes obs erved on an electrocardiogram performed on admission to the hospital. Conclusions: The measurement of myosin heavy-chain fragments was usefu l in the diagnosis of previous rhabdomyolysis up to 12 days. The role of TnT was negligible as an indicator of cardiac muscle damage in pati ents with severe rhabdomyolysis. Cardiac TnI is a more tissue-specific marker for myocardial damage even with concurrent rhabdomyolysis.-