Recurrent Motor Branch Neuropathy in Carpal Tunnel Syndrome: An Ultrasonography Study

Purpose or Learning Objective: To evaluate the occurrence of ultrasonography (US) signs of recurrent motor branch (RMB) neuropathy in patients with carpal tunnel syndrome (CTS) and thenar muscle denervation and to correlate imaging findings with clinical and electrophysiologic data.

Methods or Background: Patients with electrophysiologic evidence of CTS and thenar muscle denervation and sex- and age-matched volunteers were recruited. In both cohorts, the RMB was measured at the level of the vertical tract. US reliability was assessed through repeated RMB measurements by two readers and the calculation of the interclass correlation coefficient (ICC). Patients were evaluated with electrodiagnostic tests and asked to respond to the Boston Carpal Tunnel Questionnaire. The statistical difference between the RMB diameter in patients and volunteers was analyzed with t tests. The correlation between the RMB diameter and other parameters was assessed using a linear mixed model.

Results or Findings: A total of 46 hands from 32 patients with CTS and 50 hands from 50 volunteers were evaluated. The intra- and interobserver agreements in nerve measurement were very good (ICC: 0.84; 95% confidence interval [CI], 0.75–0.90) and good (ICC: 0.79; 95% CI, 0.69–0.87). The RMB diameter was significantly larger in patients than in volunteers (P < 0.0001). No statistically significant correlation was found between the RMB diameter and other variables except for body mass index and the median nerve cross-sectional area.

Conclusion: US is reliable to identify the RMB and characterize its abnormalities. In the patient cohort, US was able to detect definitive signs of RMB compression neuropathy.

Publication History

Article published online:
26 May 2023