The enzyme that exists chiefly in skeletal muscle, heart, and brain and rises early in muscular dystrophy and myocardial infarction is which of the following?

• A. Lipase
• B. Transaminase
• C. Lactate dehydrogenase
• D. Creatine kinase

Answer: (D)

Creatine kinase is the enzyme most characteristic here because it is highly concentrated in tissues with rapid energy demands—skeletal muscle, heart, and brain. When these tissues are damaged, such as in muscular dystrophy or myocardial infarction, CK leaks into the bloodstream earlier than many other enzymes, making it one of the first markers to rise. Its isoforms align with the tissues involved (CK-MM in skeletal muscle, CK-MB in heart, CK-BB in brain), which explains why damage to these areas shows a prompt CK increase. In contrast, lipase mainly reflects pancreatic activity, transaminases are more liver-focused (with some representation in muscle and heart but not as tissue-specific), and lactate dehydrogenase is widespread in many tissues, making them less specific and less early indicators for these conditions.