Unlike polymyositis and dermatomyositis, cardiac muscle involvement in inclusion body myositis (IBM) is uncommon, and any such involvement is unlikely to be due to IBM itself. Physicians routinely check cardiac troponins in subjects with putative inflammatory myositis and there is a risk of overdiagnosis of cardiac muscle involvement, primarily in IBM, but also in other skeletal muscle disorders.
This occurs when Troponin-T is used as the marker. Unlike Troponin-I, which is specific for the heart, Troponin-T is produced by regenerating skeletal muscle fibres, and therefore could be elevated with ongoing skeletal muscle damage (and regeneration).
The same applies to CK-MB, which is also produced by regenerating skeletal muscle, and therefore is not specific for cardiac damage when there is ongoing skeletal muscle destruction. The suspicion that such elevation- for Troponin-T or CK-MB- is not due to cardiac causes, is strengthened by a normal BNP or N-terminal ProBNP and a normal Echo.
Therefore, the only safe way to rule out cardiac muscle involvement in such patients is to test for Troponin-I. Unfortunately, many labs, including ours, routinely test for Troponin-T.
This occurs when Troponin-T is used as the marker. Unlike Troponin-I, which is specific for the heart, Troponin-T is produced by regenerating skeletal muscle fibres, and therefore could be elevated with ongoing skeletal muscle damage (and regeneration).
The same applies to CK-MB, which is also produced by regenerating skeletal muscle, and therefore is not specific for cardiac damage when there is ongoing skeletal muscle destruction. The suspicion that such elevation- for Troponin-T or CK-MB- is not due to cardiac causes, is strengthened by a normal BNP or N-terminal ProBNP and a normal Echo.
Therefore, the only safe way to rule out cardiac muscle involvement in such patients is to test for Troponin-I. Unfortunately, many labs, including ours, routinely test for Troponin-T.
