Trapezius CMAP amplitude asymmetry in accessory neuropathy

Area of Science:

• Neurology
• Neurophysiology

Background:

• Accessory neuropathy diagnosis commonly relies on upper trapezius electrodiagnostic measurements.
• Previous studies on middle and lower trapezius recording focused primarily on latency, not amplitude.

Observation:

• Three patients with unilateral accessory neuropathy post-surgery underwent accessory nerve conduction studies.
• Recordings were taken from upper, middle, and lower trapezius muscles using surface electrodes.

Findings:

• While latency values were mostly normal, significant side-to-side compound muscle action potential (CMAP) amplitude decrements (71-95%) were observed in patients A and B across all sites.
• Patient C showed similar amplitude decrements in the lower trapezius recording.

Implications:

• Side-by-side amplitude comparisons in the middle and lower trapezius muscles may significantly enhance the sensitivity of accessory neuropathy electrodiagnosis.
• This approach offers a valuable tool for identifying accessory nerve dysfunction, particularly after surgical interventions.