04) A 40 year old woman present with calf pain at night. She was recently started on statin drug for hyper cholesterolemia.After 2 weeks her muscle pain worsens, raising suspicions of myotosis.which of the following is best bio marker to indicate myotosis in this women? A) Aldolase -A B) AST C) Creatine kinase D) LDH1 E) Trophonin i
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The answer is confirmed. Here is the full explanation:
Answer: C) Creatine Kinase (CK)
Why CK is the correct answer
Creatine Kinase (CK) - also called creatine phosphokinase (CPK) - is the gold-standard biomarker for skeletal muscle injury/myositis. It is the most sensitive and specific marker for muscle cell damage.
In the context of statin-induced myopathy, this is directly supported by the textbook Rheumatology, 2-Volume Set (2022, Elsevier):
"Clinically significant myopathy, defined as an elevation in serum creatine kinase to greater than 10 times normal in association with muscle symptoms, occurred in less than 0.5% of patients in large clinical trials."
CK leaks out of damaged muscle fibers into the bloodstream. The spectrum of statin-induced muscle disease is:
| Condition | Symptoms | CK Level |
|---|---|---|
| Myalgia | Pain/soreness | Normal |
| Myositis | Pain + weakness | Elevated (>3-10x normal) |
| Rhabdomyolysis | Severe weakness, dark urine | Extremely elevated (>10,000 U/L) |
After stopping the statin, serum CK concentrations return to normal over days to weeks - confirming it tracks disease activity.
Why the other options are wrong
| Option | Marker | Why Incorrect |
|---|---|---|
| A) Aldolase-A | Glycolytic enzyme | Can be elevated in muscle disease but is less specific and sensitive than CK; used more in older literature |
| B) AST | Liver enzyme | Non-specific; elevated in liver disease, hemolysis, and many other conditions |
| D) LDH1 | LDH isoform 1 | LDH1 is the cardiac isoform (heart/RBC). Muscle damage elevates LDH5 (skeletal muscle isoform), not LDH1 |
| E) Troponin I | Cardiac-specific | This is a cardiac biomarker for myocardial injury (MI), not skeletal muscle. Troponin I is not released in skeletal myositis |
Key Teaching Points
- CK-MM is the isoform released in skeletal muscle damage (vs. CK-MB from cardiac muscle).
- Statins inhibit HMG-CoA reductase and also reduce coenzyme Q10 (ubiquinone) synthesis, which impairs muscle cell energy production - this is the proposed mechanism for muscle toxicity.
- Risk of severe rhabdomyolysis increases with concurrent use of cyclosporine, gemfibrozil, macrolide antibiotics, azole antifungals, or in patients with hypothyroidism.
- Management: discontinue the statin; CK levels and symptoms resolve within days to weeks.
- Rheumatology, 2-Volume Set (2022, Elsevier), Statin Drug-Associated Muscle Syndromes section
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