From the Guidelines
New onset weakness should be evaluated with a thorough physical examination, including neurological screening tests and assessment of mobility and muscle strength.
Evaluation Components
- Conduct frequent, serial neurologic examinations with an emphasis on cranial nerve palsies, swallowing ability, respiratory status, and extremity strength 1
- Focus on respiratory and bulbar function, including respiratory rate, lung field auscultation, and work of breathing 1
- Obtain serial objective data through spirometry, EtCO2 monitoring, blood gas analysis, or other tests 1
- Assess swallowing ability to determine if the patient can safely consume liquids or solids 1
- Consider neuromuscular assessment for patients with weakness, including assessment for treatable causes of hand weakness and characterization of any peripheral neuropathy present 1
Laboratory Testing
- CK levels may be elevated in patients with muscle weakness, but can also be normal in some cases 1
- EMG and nerve conduction studies can be useful in evaluating suspected muscle disease 1
- Muscle biopsy may be necessary for histology, histochemistry, and enzyme assay 1
Special Considerations
- Immune-related adverse events should be considered in patients treated with immune checkpoint inhibitor therapy, and managed accordingly 1
- Rheumatologic and neurologic consultation may be necessary for patients with severe or complex cases of muscle weakness 1
From the Research
Evaluation of New Onset Weakness
The evaluation of new onset weakness involves a thorough clinical history and examination to determine the underlying cause. Key aspects of the clinical history include:
- The patient's age at symptom onset 2
- Any identified inciting factors 2
- Tempo of symptom progression 2
- Pattern of weakness 2, 3
- Associated symptoms and signs 2, 3
Clinical Examination
A thorough neurologic examination is essential to localize the lesion and generate a differential diagnosis. The examination should include:
- Objective documentation of the patient's loss of strength 4
- A neurologic survey 4
- Search for patterns of weakness and extramuscular involvement 4
- Cranial nerves testing and tests for autonomic dysfunction 3
Diagnostic Approach
The diagnostic approach to new onset weakness involves:
- Distinguishing weakness from fatigue or asthenia 4
- Determining the pattern and severity of weakness, associated symptoms, medication use, and family history 4
- Considering the possibility of infectious, neurologic, endocrine, inflammatory, rheumatologic, genetic, metabolic, electrolyte-induced, or drug-induced causes 4
- Using laboratory or radiologic studies to confirm a specific cause of weakness 4
- Pursuing a tiered progression of laboratory studies if the diagnosis remains unclear 4
Localization-Based Evaluation
A localization-based evaluation involves considering the site of defect in the motor unit pathway, including: