Elevation of CK-2 (MB) Isoenzyme in Myocardial Infarction
Elevation of CK-2 (MB) isoenzyme is typically seen in myocardial infarction (option D). The evidence strongly supports this as the correct answer, with multiple guidelines confirming the specific association between CK-MB elevation and cardiac injury.
Understanding CK-MB and Cardiac Biomarkers
CK-MB (Creatine Kinase-MB) is an isoenzyme of creatine kinase that has historically been used as a biomarker for myocardial damage. According to the European Society of Cardiology guidelines:
- CK-MB is more specific for myocardial damage than total CK due to its greater concentration in cardiac versus skeletal myocytes 1
- While CK-MB constitutes 1-3% of the CK in skeletal muscle, its elevation is particularly characteristic of myocardial injury 1
- The time course of CK-MB elevation shows a rise within 3-4 hours after myocardial infarction, with peak levels at 24 hours and normalization within 24-36 hours 1
Comparison with Other Answer Options
Let's examine why the other options are incorrect:
Head trauma (A): Head trauma typically causes elevation of total CK, not specifically the MB isoenzyme. The MB isoenzyme is cardiac-specific and not significantly elevated in isolated head injuries.
Multiple sclerosis (B): There is no evidence in the provided literature linking multiple sclerosis to CK-MB elevation. MS is a neurological condition that doesn't typically cause cardiac damage.
Muscular dystrophy (C): While muscular dystrophy can cause elevation of total CK due to skeletal muscle damage, it doesn't specifically elevate the MB isoenzyme in the absence of cardiac involvement. As noted in the guidelines, "In conditions of 'false positive' elevated CK-MB such as skeletal muscle trauma, troponins will clarify any cardiac involvement" 1.
Evolution of Cardiac Biomarkers
It's important to note that while CK-MB was historically the gold standard for diagnosing myocardial infarction, cardiac troponins (troponin T and I) have now superseded CK-MB as the preferred biomarkers:
- "Cardiac troponin T or troponin I are the preferred markers of myocardial necrosis and are more specific and more reliable than traditional cardiac enzymes such as creatine kinase (CK) or its isoenzyme MB (CK-MB)" 1
- "The advantage of cardiac troponin over other biomarkers of necrosis has been firmly established in clinical studies" 1
Clinical Significance of CK-MB Elevation
Despite being replaced by troponins as the preferred biomarker, CK-MB elevation remains clinically significant:
- Even small elevations of CK-MB with normal total CK can indicate "microinfarction," which is associated with increased risk and warrants aggressive treatment 2
- CK-MB measurements are still valuable in certain clinical scenarios, such as detecting reinfarction, as troponins remain elevated for longer periods (4-14 days vs. 24-36 hours for CK-MB) 3
In conclusion, among the given options, myocardial infarction is the condition most specifically associated with elevation of the CK-MB isoenzyme.