Somatosensory evoked potential from S1 nerve root stimulation

Area of Science:

• Neuroscience
• Clinical Electrophysiology

Background:

• Somatosensory evoked potentials (SEPs) are crucial for assessing the integrity of the somatosensory pathway.
• Assessing proximal nerve root function, particularly the first sacral (S1) nerve root, presents diagnostic challenges.

Purpose of the Study:

• To detect cerebral potentials evoked by proximal S1 nerve root stimulation.
• To investigate the latency and amplitude of these S1 nerve root evoked potentials.
• To evaluate the clinical utility of this technique in diagnosing S1 nerve root lesions.

Main Methods:

• Stimulation of the S1 nerve root was performed using a needle electrode inserted via the S1 dorsal foramen in 20 healthy subjects and 5 patients.
• Cerebral potentials were recorded, and latencies and amplitudes of the first cerebral potentials (P20) were measured.
• Tibial nerve SEPs were also recorded for comparison.

Main Results:

• Reproducible cerebral evoked potentials (P20) were identified in 36 of 40 limbs of healthy subjects with a mean latency of 19.8 ± 1.6 ms.
• The mean amplitude of the P20-N30 component was 1.2 ± 0.9 μV.
• In patients with sciatic or tibial nerve injury, tibial nerve SEP P40 was absent, but S1 nerve root SEP P20 was identifiable on the affected side.

Conclusions:

• Proximal S1 nerve root stimulation can elicit reproducible cerebral potentials.
• This technique is potentially useful for detecting S1 nerve root lesions and other proximal somatosensory pathway disorders.
• Combined with tibial nerve SEP, it can aid in differentiating peripheral nerve from central pathway lesions.