A patient has high plasma myoglobin but normal troponin I levels. What is the most likely condition?

In this scenario, a patient presents with high plasma myoglobin and normal troponin I levels. Myoglobin is a protein released into the bloodstream following muscle damage, and its elevation is commonly associated with injury to skeletal muscle. Troponin I, on the other hand, is a protein found specifically in cardiac muscle and is a sensitive marker for myocardial injury.

When myoglobin levels are high without an accompanying increase in troponin I, it strongly indicates that the source of the injury is related to skeletal muscle rather than cardiac muscle. This combination of elevated myoglobin and normal troponin I levels suggests that there has been a skeletal muscle injury, which does not indicate a myocardial injury.

While options like acute myocardial infarction and unstable angina relate directly to cardiac issues, the absence of elevated troponin I effectively rules out these conditions, as troponin would typically be elevated in cases of myocardial injury. Therefore, the presence of high myoglobin with normal troponin I levels confirms the likelihood of a skeletal muscle injury rather than any myocardial or significant skeletal muscle injury that would also elevate troponin. Thus, this situation does not represent evidence of myocardial injury or significant skeletal muscle injury.