Which of the following disorders is not associated with an elevation of serum creatine kinase?

• A. Cerebrovascular accidents
• B. Hypothyroidism
• C. Bone disease
• D. Intramuscular injection

Answer: (C)

Serum creatine kinase rises when skeletal muscle is damaged, because the enzyme leaks out of injured muscle cells into the bloodstream. CK is most abundant in skeletal muscle (CK-MM), with smaller amounts in heart (CK-MB) and brain (CK-BB), so conditions that injure muscle or cause metabolic muscle stress typically elevate CK levels.

An intramuscular injection directly injures muscle fibers, releasing CK into the blood. Hypothyroidism can cause a myopathy characterized by muscle fiber damage and increased CK as a result. A cerebrovascular accident (stroke) can be associated with elevated CK if there’s concomitant muscle injury or rhabdomyolysis from immobility or prolonged confinement. In contrast, bone disease affects bone tissue, not muscle, so it does not cause the leakage of CK into the serum. Therefore, bone disease is not associated with an elevation of serum creatine kinase.