Relationship Between Cervical Nerve Root Entrapment Due to Cervical 6-7 Foraminal Stenosis and Sensory Nerve Action Potentials in Nerve Conduction Study

Objective To compare the sensory nerve action potentials (SNAPs) between patients with cervical 6-7 foraminal stenosis (FS) and those without. Methods We enrolled patients who underwent a bilateral nerve conduction study (NCS) between January 2016 and December 2017. The FS group (n=35) included patients whose lesion was located at C6-7 FS. The non-FS group (n=75) had no lesions at C6-7 foramen. The amplitudes and latencies of SNAPs on the affected side were compared between the two groups. The proportion of those with abnormal SNAP responses was also evaluated. Results Compared with the non-FS group, the FS group had a significantly lower amplitude (30.5 vs. 40.2 µV; age-adjusted p<0.001) and a longer latency (3.31 vs. 3.17 ms; age-adjusted p=0.001) of the median nerve. Abnormal amplitude was observed in 20.0% of the FS group and 4.0% of the non-FS group (age-adjusted p=0.007), and abnormal latency was observed in 45.7% of the FS group and 26.7% of the non-FS group (age-adjusted p=0.010). The median SNAP ratio between the affected side and the unaffected side was not significantly different between the two groups. Conclusion Patients with C6-7 FS had a lower amplitude and a longer latency of the median nerve than did those without. Abnormal SNAP amplitude and latency were significantly more common in patients with FS. SNAP amplitude may be used as a predictor of cervical FS. Keywords: Electrodiagnosis; Cervical foraminal stenosis; Sensory nerve action potential; Median nerve