2026 Workshop Handout Bundle-W127G Proximal Upper-Extremity Nerve Conduction Studies

W127G Proximal Upper-Extremity Nerve Conduction Studies - Alrajeh Benson

Pdf Summary

This workshop presents three proximal upper-extremity nerve conduction studies that can help identify shoulder-girdle neuropathies and brachial plexus lesions:

- <strong>Biceps motor study (musculocutaneous nerve):</strong> Useful when evaluating suspected musculocutaneous neuropathy, upper-trunk or lateral-cord plexopathy, and traumatic or postsurgical nerve injury. Record the response over the biceps, stimulating at the axilla and Erb’s point. Compare CMAP amplitudes between sides; an asymmetry of about 40% may suggest a lesion. The stated normal latency is ≤5.7 ms.
- <strong>Deltoid motor study (axillary nerve):</strong> Helps assess axillary neuropathy, deltoid weakness, upper-trunk or posterior-cord plexopathy, and shoulder injury. Record over the middle deltoid and stimulate at the axilla and Erb’s point. A side-to-side amplitude asymmetry of about 40% may be significant. The stated latency is ≤4.9 ms; lower normal CMAP limits are 7.6 mV for men and 6.5 mV for women.
- <strong>Posterior antebrachial cutaneous (PAC) sensory study:</strong> Can help localize radial neuropathy at the spiral groove, distinguish it from posterior interosseous neuropathy, and evaluate plexopathy or focal PAC injury. Stimulate the radial nerve in the upper arm before the PAC branch and record over the posterior forearm. A side-to-side amplitude asymmetry of about 40% may suggest a lesion.

Across all three studies, side-to-side comparisons are often more informative than absolute amplitudes, which can vary with body size and other factors. Proximal stimulation may be difficult or poorly tolerated, and surface distance measurements can be inaccurate; careful technique and caliper measurements are recommended. PAC responses may be small and vulnerable to electrode-placement errors, motor-potential contamination, and excessive stimulus intensity.

Keywords

biceps motor study

deltoid motor study

posterior antebrachial cutaneous study

musculocutaneous nerve

axillary nerve

brachial plexus lesion

shoulder girdle neuropathy

side-to-side amplitude asymmetry

nerve conduction studies

ncs

proximal upper extremity