From the Guidelines
The workup for muscle weakness should begin with a thorough history and physical examination, including complete rheumatologic and neurologic history, and examination of the skin for findings suggestive of dermatomyositis, as recommended by the American Society of Clinical Oncology clinical practice guideline 1. The diagnostic work-up should include blood testing to evaluate muscle inflammation, such as CK, transaminases (AST, ALT), lactate dehydrogenase (LDH), and aldolase, as well as troponin to evaluate myocardial involvement and other cardiac testing, such as echocardiogram, as needed 1. Some key points to consider in the workup include:
- Inflammatory markers (ESR and CRP) should be included in the initial laboratory tests 1
- Electromyography (EMG), imaging (MRI), and/or biopsy should be considered on an individual basis when diagnosis is uncertain and overlap with neurologic syndromes, such as myasthenia gravis, is suspected 1
- Paraneoplastic autoantibody testing for myositis and neurologic conditions, such as myasthenia gravis, may also be necessary 1
- A muscle biopsy can help to distinguish among various neuromuscular diseases and genetic testing should be considered for suspected hereditary myopathies 1 The most recent and highest quality study recommends a comprehensive approach to the workup of muscle weakness, including a combination of history, physical examination, laboratory tests, and additional testing as needed, to identify the underlying cause and allow for appropriate targeted treatment 1.
From the Research
Clinical Approach to Muscle Weakness
The evaluation of muscle weakness involves a thorough clinical approach, including a detailed history and physical examination, to determine the underlying cause of the weakness.
- The patient's age at symptom onset, any identified inciting factors, tempo of symptom progression, pattern of weakness, and associated symptoms and signs are all important diagnostic clues in the evaluation of a patient presenting with muscle weakness 2.
- A stepwise approach to narrowing the differential diagnosis relies on the history and physical examination combined with knowledge of the potential etiologies 3.
Diagnostic Tools and Tests
Various diagnostic tools and tests can be used to evaluate muscle weakness, including:
- Medical Research Council Manual Muscle Testing scale to grade muscle weakness objectively 3
- Laboratory testing, such as electrolyte, thyroid-stimulating hormone, and creatine kinase measurements 3, 4
- Electromyography to confirm the presence of a myopathy or to evaluate for a neuropathy or a disease of the neuromuscular junction 3, 4
- Muscle biopsy to diagnose certain myopathies 5, 4
- Magnetic resonance imaging to guide muscle biopsy or to evaluate for acute neurologic conditions 3
Patterns of Weakness and Associated Symptoms
The pattern of weakness and associated symptoms can provide important clues to the underlying cause of the weakness.
- Asymmetric weakness is more common in neurologic conditions, whereas pain is more common in neuropathies or radiculopathies 3
- Frailty and sarcopenia are clinical syndromes occurring in older people that can present with generalized weakness 3
- Proximal muscle weakness can present acutely or subacutely and requires early diagnosis to prevent life-threatening complications such as respiratory failure and cardiac disturbances 6