Screening for Upper Limb Weakness
Screen upper limb weakness by performing manual muscle testing of six key antagonist muscle pairs (pectoralis major/posterior deltoid, biceps/triceps, and radial wrist flexors/extensors), which provides high sensitivity (84-92%) for detecting neuropathic conditions and can identify weakness in nearly all symptomatic limbs. 1
Initial Clinical Assessment
History Taking
- Assess for specific symptoms including pain, weakness, and numbness/tingling in the upper extremity 1, 2
- Inquire about functional limitations in activities of daily living, self-care skills, writing, and computer use 3
- Document any history of trauma, repetitive activities, or occupational exposures that may contribute to nerve compression 4
Physical Examination Components
Muscle Strength Testing:
- Test six representative muscles as a screening approach: 1
- Pectoralis major and posterior deltoid (shoulder function)
- Biceps and triceps (elbow flexion/extension)
- Radial flexor of wrist and short radial extensor of wrist (wrist function)
- Use manual muscle testing with the Medical Research Council (MRC) scale for grading 3
- This abbreviated examination achieves sensitivity of 84-92% for detecting symptomatic neuropathic conditions 1
Comprehensive Examination (when screening is positive):
- Expand to testing 14-16 individual muscles for complete assessment 4, 2
- Assess sensibility in 7 homonymous innervated territories 4, 2
- Evaluate nerve mechanosensitivity at 10-20 locations along nerve trunks 4, 2
Interpretation and Follow-up
Positive Screening Results
- Weakness detected in one or more of the six screening muscles warrants further comprehensive neurological examination 1
- The positive predictive value is 0.93 when patterns of weakness correlate with anatomical nerve distributions 2
- Agreement between findings and symptoms yields diagnostic confidence with post-test probability of 0.81-0.88 2
Pattern Recognition
- Identify topographical patterns suggesting focal neuropathies based on anatomical nerve distributions 2
- Look for concordance between muscle weakness, sensory deficits, and nerve mechanosensitivity in anatomically related territories 4
- Consider related locations of neuropathy (double crush phenomenon or regional spread patterns) 4
Important Clinical Caveats
Specificity Limitations:
- The six-muscle screening approach has moderate specificity (50-70%), meaning weakness may be detected in non-symptomatic limbs 1
- False positives occur, requiring confirmatory comprehensive assessment before definitive diagnosis 1
- Inter-rater reliability is moderate (kappa = 0.58), so findings should be correlated with clinical context 1
Special Populations:
- In Duchenne muscular dystrophy, upper extremity assessment becomes relevant in late ambulatory stages using the Brooke upper extremity scale 3
- Post-stroke patients may have ipsilateral upper limb weakness that recovers within one month but may not completely resolve 5
- Functional (non-organic) weakness requires specific validated examination techniques to differentiate from structural neurological disease 6
Monitoring and Surveillance
- For progressive conditions like muscular dystrophy, test upper extremity strength every 6 months in early stages 3
- Serial assessments help identify deviations from expected clinical course and monitor treatment response 3
- Use standardized motor function scales (Brooke upper extremity scale, Hammersmith motor scales) for longitudinal tracking 3