Introduction: Recording at various levels of the somatosensory pathway is often used in somatosensory evoked potentials to mixed nerve stimulation (SEP), but not in dermatomal somatosensory evoked potentials (DSEP) in which only the cortical potential is usually recorded. The aim of our study was to compare the recordings of upper limb DSEP at Erb point, cervical cord, and subcortical and cortical levels with SEP recordings in healthy subjects and patients with cervical radiculopathy.
Patients and methods: 17 patients with clinical history, MRI and electromyography consistent with cervical radiculopathy and 17 healthy subjects were included. Median and ulnar nerves were stimulated at the wrist; and C6, C7 and C8 dermatomes at the 1st, 3rd and 5th fingers respectively. All the potentials obtained with SEP and DSEP were compared between controls and patients by t test for independent samples. We also used Pearson s correlation for height/latencies, weight/amplitude and age/peripheral nerve conduction velocity (PNCV).
Results: DSEP potentials were of similar morphology of those observed in SEP but had longer latencies and smaller amplitudes. We found a positive correlation between height and latencies, and a negative association of weight with amplitude of peripheral potential, and age/PNCV. No difference between controls and the neurological intact segments of patients was found. 13 patient had DSEP altered while only 5 of them had altered SEP recorded. The most common finding was prolongation of the conduction time of the segment N9 N13 on DSEP recordings.
Conclusion: We found that it is possible to record and to identify all the potentials in DSEP as observed in the SEP. On cervical radiculopathy, DSEP with the present technique increase the sensitivity and give some additional and useful information regarding the extension and localization of the pathology. Besides, DSEP recording is a non invasive technique, non traumatic and well tolerated for our patients.