Comparison of the Interference Effects on Somatosensory Evoked Potential from Tonic, Burst, and High-dose Spinal Cord Stimulations

Abstract

Spinal cord stimulations have been used widely to treat intractable neuropathic pain. The conventional spinal cord stimulation paradigm, the "tonic" type, suppresses excessive activation of wide dynamic range neurons in the dorsal horn via the collateral branch from the dorsal column. Therefore, preserved dorsal column function is an important prerequisite for tonic spinal cord stimulations. A tonic spinal cord stimulation requires eliciting paresthesia in the painful area due to stimulation of the dorsal column and dorsal root. Recent spinal cord stimulation paradigms, including burst and high-dose, are set below the paresthesia threshold and are proposed to have different pain reduction mechanisms. We conducted an interference study of these different stimulation paradigms on the somatosensory evoked potential (SEP) to investigate differences in the sites of action between tonic and new spinal cord stimulations. We recorded posterior tibial nerve-stimulated SEP in seven patients with neuropathic pain during tonic, burst, and high-dose stimulations. The total electrical energy delivered was calculated during SEP-spinal cord stimulation interference studies. High-dose stimulations could not reduce the SEP amplitude despite higher energy delivery than tonic stimulation. Burst stimulation with an energy similar to the tonic stimulation could not reduce SEP amplitude as tonic stimulation. The study results suggested different sites of action and effects on the spinal cord between the conventional tonic and burst or high-dose spinal cord stimulations.

Keywords: burst stimulation; high-dose stimulation; somatosensory evoked potentials; spinal cord stimulation; tonic stimulation.

Fig. 1

TEED and SEP change ratios. Total electrical energy delivered (TEED) at paresthesia threshold, maximum paresthesia threshold and somatosensory evoked potential (SEP) change ratio (n = 5–7). SEP change ratio was calculated as the amplitude of SEP during spinal cord stimulation divided by the amplitude of control SEP at paresthesia threshold (n = 5) or maximum paresthesia threshold (n = 7) stimuli. PT, paresthesia threshold; MPT, maximum paresthesia threshold; HD, high-dose.

Fig. 2a

Comparisons between tonic and burst stimulations. Effects of spinal cord stimulation on posterior tibial nerve-stimulated somatosensory evoked potential (SEP). The P40/N50 is almost absent during tonic stimulation (A, B) but is clearly preserved during burst spinal cord stimulation (C, D). The total electrical energy delivered (TEED) of tonic spinal cord stimulation (B) = 7.3 mA² × 325 ohms × 30 Hz × PW 200 μs = 1.04 × 10⁸ (mA² × Ω × Hz × μs) = 104 microwatts (μW). The TEED of burst spinal cord stimulation (D) = 0.0014A × 0.0014A × 325 ohms × 40 Hz × 5 × PW 0.001 sec = 1.27 × 10⁸ (mA² × Ω × Hz × μs) = 127 microwatts (μW). PTN; Posterior tibial nerve.

Fig. 2b

Comparisons between tonic and high-dose stimulations. Changes in somatosensory evoked potentials (SEP) during tonic and high-dose spinal cord stimulation, in comparison to the controls (A, D, and H), demonstrating absent P40/N50 during tonic spinal cord stimulation (B, C, and F) and preserved P40/N50 during high-dose spinal cord stimulation (E, G). Total electrical energy delivered (TEED) is shown. PTN; Posterior tibial nerve. μW = microwatts.

Fig. 3

Somatosensory evoked potentials during burst, high-dose, and tonic stimulations. Serial somatosensory evoked potential (SEP) recordings for the interactions of burst (B, C), high-dose (E, F), and tonic (H, I) spinal cord stimulations (SCSs) are shown. The apparent reduction in P40/N50 amplitude is only seen during tonic spinal cord stimulation (I). Control SEPs (A, D, G, and J) are shown for comparisons. The values of total electrical energy delivered (TEED) are shown. PTN, Posterior tibial nerve; PT, paresthesia threshold; MPT, maximum paresthesia threshold. μW = microwatts.