Background
The diagnosis of nerve root injury and its corresponding roots are visibly difficult. Sensory nerve action potential (SNAP) decreases in amplitude when the lesion is present at or distal to the dorsal root ganglion. Previous study showed that the amplitude of SNAP on the impinged side were comparatively lower than the unaffected side in foraminal L5 nerve root entrapment. The aim of study is to investigate the latency and amplitude of SNAP in patients with cervical foraminal stenosis relative to unimpeded patients.
Methods
As a retrospective study, we enrolled a total of 751 patients who visited the electromyography (EMG) clinic from January to December 2017. The exclusion criteria include patients with median neuropathy, ulnar neuropathy, peripheral neuropathy and brachial plexopathy diagnosed by EMG. Patients examined by the unilateral nerve conduction study or patients with no MRI findings were excluded. Bilateral SNAPs were recorded for the median nerve at third digit and the ulnar nerve at fifth digit. This study employed methods to assess the onset to peak amplitude and the peak latency.
The patients were divided into two groups based upon the results of MRI. Group A (29 patients) included patients whose lesion was located at C6-7, C7-T1 foraminal stenosis. In group B (55 patients), there are no lesions at C6-7, C7-T1 foraminal stenosis.
The amplitude and latency of SNAPs on the affected side to that on the unaffected side were compared between group A and B. The abnormal SNAP responses were compared between two groups. This study set up the cut-off value as 20μV in amplitude of median nerve, as 10μV in amplitude of ulnar nerve, as 3.6ms in latency of median and ulnar nerve.
Results
The amplitudes of median nerve and ulnar nerve for group A were lower than group B (p = 0.001, 0.002, respectively, by t-test). On the other hand, the latency period of median nerve for group A was longer than group B (p = 0.010, by t-test). The latency of ulnar nerve for group A was longer than group B, but between the two groups, there were no statistical differences (p = 0.237). The abnormalities of SNAP amplitude and latency were more frequent in patients with foraminal stenosis.
Conclusions
Patients with foraminal stenosis had a significantly longer latency period of median nerve and a lower amplitude of median and ulnar nerve than those without foraminal stenosis. SNAP could be an useful additional parameter to diagnose the cervical foraminal stenosis. |
