Value of MUNE versus compound muscle action potential in assessing motor unit loss in patients with carpal tunnel syndrome

The most prevalent nerve entrapment disorder, known as carpal tunnel syndrome (CTS), is brought on by wrist-based median nerve compression. Focal demyelination progresses to axonal dysfunction as the condition worsens. In order to detect motor unit (MU) loos, this study compares two motor unit number estimation (MUNE) techniques with compound muscle action potential (CMAP) amplitude. The CMAP amplitude and MUNE of the median nerve in 137 hands of 70 neurophysiologically approved CTS patients, aged 40.27 ± 10.06 years were examined. Another 90 hands from 56 healthy volunteers who are age- and gender-matched serve the control group.

In contrast to 192.5 and 248.5 in controls, the median nerve values of incremental and adapted multipoint stimulation (aMPS) MUNE in CTS patients were, respectively, 111 and 133 (p < 0.0001). Patients with severe CTS compared to those with mild CTS using both methods had significantly lower MUNE. MUNE values are the same regardless of gender or hand dominance. In comparison to MUNE methods (cutoff values of 106.5 and 203, respectively), CMAP amplitude had a sensitivity and specificity of more than 60% in detecting MU loss (cutoff value of 6.85 mV). The CTS grading had no effect on the CMAP amplitude. MUNE values had positive with CMAP amplitude and negative with CTS grading and Phalen test positivity.

When identifying motor nerve involvement in CTS patients, the MUNE technique is more accurate than a standard motor nerve conduction study (NCS). It was emphasized that MUNE evaluation in determining MU loss in the early stages of CTS may be helpful in diagnosis and treatment. There was no correlation between handedness and the number of MUs as determined by MUNE techniques. Both methods almost equally identify MU loss and have the same sensitivity and specificity.