Spinal cord stimulation inhibits cortical somatosensory evoked potentials significantly stronger than transcutaneous electrical nerve stimulation.

BACKGROUND Despite the good clinical results elicited by spinal cord stimulation (SCS), the physiological basis of action of SCS is widely unknown. Inhibition of somatosensory evoked potential (SEP) amplitudes by SCS has been described, but it is unclear whether this displays dose dependency. Moreover, it is unknown whether the pain-relieving effect elicited by SCS correlates with the inhibition of SEPs. Finally, this study aimed to answer the question whether there is a difference in the effect on SEPs between SCS and transcutaneous electrical nerve stimulation (TENS), thus between central nervous system stimulation and peripheral nervous system stimulation. METHODS Ten patients (4 men and 6 women, age range 40-77 years) with neuropathic lower limb pain were included in the study. All patients had implanted SCS systems with percutaneous type electrodes. Cortical SEPs under SCS and TENS were measured without stimulation, under stimulation at perception threshold (PT), and at maximal threshold (MT) in a crossover design. RESULTS Cortical SEP amplitudes were significantly inhibited by SCS. Stimulation at PT and at MT both led to a statistically significant inhibition of the SEP amplitude. The difference between amplitude reduction at PT and MT showed a tendency towards significance. The degree of SEP amplitude inhibition did not correlate with pain relief. Inhibition of SEP amplitudes by TENS was weaker than that elicited by SCS. The average percentage of amplitude reduction at MT was twice as high under SCS as it was under TENS. No effects on SEP latencies were seen. CONCLUSIONS SCS exerts a significantly stronger inhibition of SEP amplitudes than TENS. The data hint at a dose dependency of SCS-induced SEP amplitude inhibition. No correlation between SEP amplitude inhibition and pain relief was found.