Troponin with Underlying Myopathy

Written by Clay Smith

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Adult patients with skeletal myopathy often have false positive high sensitivity troponin T (but not troponin i), because the assay cross reacts with skeletal muscle troponin T.

Why does this matter?
Patients with myopathies often have elevated troponin, even if they have no known cardiomyopathy.  This may lead to increased, and potentially unnecessary, invasive testing.  What's going on here?

Troponin tricks - hs-TnT is a problem
This was an analysis of 74 adults with skeletal myopathies: "myotonic dystrophy types 1 and 2, nondystrophic myotonias, Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), facioscapulohumeral muscular dystrophy, limb girdle muscular dystrophies, X-linked myopathy with postural muscle atrophy (XMPMA), inclusion body myopathy, and inflammatory myopathies."  All underwent extensive cardiac workup: ECG, biomarkers, cardiac MRI, and some had coronary CTA.  Most had no cardiac involvement; 23% did to some extent.  They found high sensitivity troponin T (hs-TnT) was elevated in almost 70% of all patients, whereas hs-Tni was only detectable in about 4%.  They gleaned, using muscle biopsy and sophisticated protein identification, that the cardiac troponin T assay was likely cross reacting with skeletal muscle troponin T, giving a false positive result.  When a patient with myopathy presents to the ED, realize that troponin T may not be the most reliable way to assess for MI.  If hs-TnT is the only assay available, serial values must be obtained for the information to be helpful in diagnosing cardiac injury.

Source
Elevated Cardiac Troponin T in Patients With Skeletal Myopathies.  J Am Coll Cardiol. 2018 Apr 10;71(14):1540-1549. doi: 10.1016/j.jacc.2018.01.070.

Peer reviewed by Thomas Davis

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