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Diagnostic Tests – Muscle Biopsy
1. For which clinical condition(s) would you use this test?
A muscle biopsy is used to diagnose primary myopathies, particularly when a structural, metabolic, inflammatory, or genetic muscle disorder is suspected. Conditions commonly diagnosed with muscle biopsy include:
2. When do you answer muscle biopsy?
You should choose muscle biopsy when the clinical scenario describes:
Proximal weakness + myalgias + suspected intrinsic muscle disease → Muscle biopsy
3. For which muscle diseases would you
not
answer muscle biopsy?
Despite overlapping symptoms of weakness, muscle biopsy is NOT the correct test in the following situations:
1. For which clinical condition(s) would you use this test?
A muscle biopsy is used to diagnose primary myopathies, particularly when a structural, metabolic, inflammatory, or genetic muscle disorder is suspected. Conditions commonly diagnosed with muscle biopsy include:
- Glycogen storage diseases
- Mitochondrial myopathies
- Dystrophinopathies (e.g., Duchenne and Becker muscular dystrophy)
- Inflammatory myopathies, such as dermatomyositis and polymyositis
2. When do you answer muscle biopsy?
You should choose muscle biopsy when the clinical scenario describes:
- Proximal muscle weakness, such as:
- Difficulty with shoulder abduction
- Trouble rising from a chair
- Associated myalgias (muscle soreness)
- Evidence of myopathy, such as:
- Elevated muscle enzymes
- Recurrent rhabdomyolysis
- A possible family history of similar symptoms, suggesting an inherited muscle disorder
Proximal weakness + myalgias + suspected intrinsic muscle disease → Muscle biopsy
3. For which muscle diseases would you
not
answer muscle biopsy?
Despite overlapping symptoms of weakness, muscle biopsy is NOT the correct test in the following situations:
- Endocrine-related myopathies
- Examples: thyroid disease, diabetes
- Appropriate tests: specific endocrine laboratory testing
- Neuromuscular junction disorders
- Example: myasthenia gravis
- Appropriate tests:
- Edrophonium (Tensilon) testing
- Anti–acetylcholine receptor antibodies
- Electromyography (EMG)
- Muscle fiber disease → muscle biopsy
- Endocrine or neuromuscular junction disease → targeted labs or electrophysiologic testing
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