Abstract 14406: Cardiac Troponin T Should not be Used to Diagnose Myocardial Injury in Patients with Skeletal Muscle Diseases
Introduction: Cardiac Troponin (cTn) T and I assays are believed to have equally high sensitivity and specificity for the diagnosis of myocardial injury. However , unlike cTnI, it is known that cTnT is expressed in fetal skeletal muscle and in regenerating skeletal muscle in adults. We hypothesised that patients with skeletal muscle diseases would have elevated cTnT but not cTnI in the absence of myocardial injury.
Methods: The study consisted of 21 hospitalised patients aged 61 ± 16 years referred for urgent cardiac investigations because of elevated cTnT and 25 ambulatory patients aged 50 ± 14 years, with different types of neuromuscular diseases selected randomly from clinic . Eleven of the hospitalised patients had pre-existing diagnoses of neuromuscular diseases , mainly muscle dystrophies and inflammatory myopathies. A new diagnosis of skeletal myopathy , mostly induced by alcohol and statins, was made in the other 10 patients. Serial measurements of serum cTnT, cTnI , creatine kinase (CK), CK-MB and NT-proBNP were performed in hospitalised patients and single ones in ambulatory patients.
Results: During a mean study period of 2.4 years, cTnT ( median: 0.08; IQR: 0.06 - 0.14 μ g/L) , CK (582 IU; 303- 3662 U/L) and CK-MB ( 24; 8 - 34 μ g/L) were persistently elevated in all patients in the hospitalised group . In contrast cTnI, measured by 2 different assays, remained normal throughout in 19 patients. NT-proBNP was 220; 88 - 338 pg/mL . ECG and echocardiograms were normal in 12 and 16 patients respectively. During follow up there were no serial changes on electrocardiography or echocardiography and no cardiovascular events occurred. Ambulatory patients had elevated CK (624 IU; 224-1190) , CK-MB (17;11-29 μ g/L) and cTnT -hs ( 0.021; 0.011 - 0.040 μ g/L ) in 19, 20 and 16 respectively. cTnI was normal in all but one patient . NT-proBNP was 47; 33 - 106 pg/mL . ECG was normal in 14 and had minor abnormalities in 6.
Conclusion: Patients with neuromuscular diseases characterised by elevation of CK have persistent elevation of CK-MB and cTnT in the absence of myocardial injury. cTnI is typically normal. It appears that the current commercial immunoassay (Roche ) cannot distinguish between cTnT of cardiac and skeletal muscle origins.
- © 2012 by American Heart Association, Inc.