The non-invasive potential: CMAP as a valid test in comparison to invasive needle EMG in Carpal Tunnel Syndrome evaluation at Chonburi hospital
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Abstract
Background: Electrodiagnosis can confirm the presence and severity of carpal tunnel syndrome. The criteria for diagnosing CTS vary; some include only nerve conduction studies, while others also incorporate needle EMG studies to confirm severe axonopathy. A disadvantage of needle EMG studies is the pain and cost associated with the needles. CMAP represents the function of the axon. Therefore, CMAP may represent spontaneous activity in needle EMG.
Methods: A retrospective cohort study was conducted on 105 patients scheduled for concluding CTS based on electrodiagnostic reports from 2019 to 2023 at Chonburi Hospital. Fifty patients underwent both nerve conduction studies and needle EMG, and they did not meet the exclusion criteria.
Results: There were 26 patients with CMAP < 5 mV and spontaneous activity found in the needle EMG study. Additionally, 6 patients had CMAP < 5 mV with no spontaneous activity detected in the needle EMG study. Furthermore, 3 patients had CMAP ≥ 5 mV with spontaneous activity found in the needle EMG study. Lastly, 15 patients had CMAP ≥ 5 mV with no spontaneous activity detected in the needle EMG study. The sensitivity was 90%, specificity was 71%, and accuracy was 82%. From logistic regression of CMAP, there is the cutoff value for CMAP was found to be 3.7 mV. In logistic regression analysis of CMAP, the cutoff value for CMAP was found to be 3.7 mV, with a specificity of 82%.
Conclusion: In electrodiagnosis for CTS, CMAP ≤ 3.7 mV can predict the presence of spontaneous activities in needle EMG studies.
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