A modified multiple point stimulation method for motor unit number estimation of the hypothenar muscles

Area of Science:

• Neurology
• Physiology
• Biomedical Engineering

Background:

• Motor unit number estimation (MUNE) is crucial for assessing neuromuscular disorders.
• Accurate MUNE relies on precise identification of single motor unit action potentials (SMUPs).
• Potential for cross-contamination of SMUPs from adjacent muscles exists.

Purpose of the Study:

• To test if SMUPs from other ulnar nerve-innervated intrinsic hand muscles inflate hypothenar MUNE.
• To quantify the impact of distant SMUPs on MUNE calculations.

Main Methods:

• Employed the multiple point stimulation method for SMUP characterization.
• Utilized multichannel recordings to differentiate SMUP origins.
• Compared MUNE calculated with and without distant SMUPs.

Main Results:

• Distant SMUPs constituted 17% of the total sample.
• MUNE was significantly higher when including all SMUPs (537 ± 290) versus only hypothenar SMUPs (423 ± 204).
• Increased MUNE correlated strongly with the proportion of distant SMUPs (r = 0.89).

Conclusions:

• Erroneous inclusion of distant SMUPs significantly distorts MUNE results.
• Careful identification of SMUP origins is essential for accurate MUNE.
• Findings highlight the need for refined MUNE techniques to avoid overestimation.