What is a non-cardiac cause of elevated plasma CKMB?

The correct answer pertains to muscular dystrophy, which is a non-cardiac condition that can lead to elevated levels of plasma creatine kinase MB (CKMB). CKMB is primarily associated with skeletal muscle and can be released into the bloodstream when there is muscle damage or injury. In conditions like muscular dystrophy, which involve progressive muscle degeneration and weakness, the muscle cells become damaged, leading to an increase in CKMB levels that is not directly related to cardiac muscle damage.

In contrast, acute myocardial infarction, coronary artery disease, and heart failure are all conditions associated with the heart, which can elevate CKMB due to the specific damage or stress placed on cardiac muscle. In these cases, elevated CKMB serves as a biomarker indicating myocardial injury or dysfunction. Thus, among the options provided, muscular dystrophy stands out as the only scenario where the source of elevated CKMB is from skeletal rather than cardiac muscle.