Elevated Cardiac Troponin T in Patients With Skeletal Myopathies
Johannes Schmid1, Laura Liesinger2, Ruth Birner-Gruenberger2
1Division of Cardiology, Department of Internal Medicine, Medical University of Graz, Graz, Austria; Division of General Radiology, Department of Radiology, Medical University of Graz, Graz, Austria.
Insights
Elevated cardiac troponin T (cTnT) in skeletal muscle disease is common, but not due to heart damage. Assays may cross-react with skeletal troponin T, causing false positives for myocardial infarction.
Area of Science:
- Biochemistry
- Cardiology
- Clinical Diagnostics
Background:
- Cardiac troponins (cTnT and cTnI) are frequently elevated in patients with skeletal muscle disease.
- This elevation occurs without evidence of underlying cardiac disease.
Purpose of the Study:
- To characterize cardiac troponin concentrations in patients with myopathies.
- To investigate the source of elevated troponin T measurements in these patients.
Main Methods:
- Measured cTnT and cTnI using high-sensitivity assays in 74 myopathy patients.
- Conducted comprehensive cardiac evaluations and analyzed skeletal muscle troponin expression via mass spectrometry.
- Utilized antibodies from commercial assays to detect protein expression.
Main Results:
- Elevated cTnT was found in 68.9% of patients, while elevated cTnI was rare (4.1%).
- cTnT levels correlated with creatine kinase and myoglobin; 30.1% met myocardial infarction criteria.
- Skeletal muscle samples showed positive bands with cTnT antibodies, identified as skeletal troponin T isoforms via mass spectrometry.
Conclusions:
- Chronic elevation of cTnT in myopathy patients is likely due to immunoassay cross-reaction with skeletal muscle troponin isoforms.
- cTnI elevation is uncommon in this population.
- This highlights a potential diagnostic challenge in differentiating cardiac from skeletal muscle troponin elevations.
Background:
Cardiac troponins are often elevated in patients with skeletal muscle disease who have no evidence of cardiac disease.
Objectives:
The goal of this study was to characterize cardiac troponin concentrations in patients with myopathies and derive insights regarding the source of elevated troponin T measurements.
Methods:
Cardiac troponin T (cTnT) and cardiac troponin I (cTnI) concentrations were determined by using high sensitivity assays in 74 patients with hereditary and acquired skeletal myopathies. Patients underwent comprehensive cardiac evaluation, including 12-lead electrocardiogram, 24-h electrocardiogram, cardiac magnetic resonance imaging, and coronary artery computed tomography. cTnT and cTnI protein expression was determined in skeletal muscle samples of 9 patients and in control tissues derived from autopsy using antibodies that are used in commercial assays. Relevant Western blot bands were subjected to liquid chromatography tandem mass spectrometry for protein identification.
Results:
Levels of cTnT (median: 24 ng/l; interquartile range: 11 to 54 ng/l) were elevated (>14 ng/l) in 68.9% of patients; cTnI was elevated (>26 ng/l) in 4.1% of patients. Serum cTnT levels significantly correlated with creatine kinase and myoglobin (r = 0.679 and 0.786, respectively; both p < 0.001). Based on cTnT serial testing, 30.1% would have fulfilled current rule-in criteria for myocardial infarction. Noncoronary cardiac disease was present in 23%. Using cTnT antibodies, positive bands were found in both diseased and healthy skeletal muscle at molecular weights approximately 5 kDa below cTnT. Liquid chromatography tandem mass spectrometry identified the presence of skeletal troponin T isoforms in these bands.
Conclusions:
Measured cTnT concentrations were chronically elevated in the majority of patients with skeletal myopathies, whereas cTnI elevation was rare. Our data indicate that cross-reaction of the cTnT immunoassay with skeletal muscle troponin isoforms was the likely cause.
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