Conventional and Kilohertz- frequency Spinal Cord Stimulation Produces Intensity- and Frequency-dependent Inhibition of Mechanical Hypersensitivity in a Rat Model of Neuropathic Pain

Background: Spinal cord stimulation (SCS) is a useful neuromodulatory technique for treatment of certain neuropathic pain conditions. However, the optimal stimulation parameters remain unclear. Methods: In rats after L5 spinal nerve ligation, the authors compared the inhibitory effects on mechanical hypersensitivity from bipolar SCS of different intensities (20, 40, and 80% motor threshold) and frequencies (50, 1 kHz, and 10 kHz). The authors then compared the effects of 1 and 50 Hz dorsal column stimulation at high-and low-stimulus intensities on conduction properties of afferent A alpha/beta-fibers and spinal wide-dynamic-range neuronal excitability. Results: Three consecutive daily SCS at different frequencies progressively inhibited mechanical hypersensitivity in an intensity-dependent manner. At 80% motor threshold, the ipsilateral paw withdrawal threshold (% preinjury) increased significantly from pre-SCS measures, beginning with the first day of SCS at the frequencies of 1 kHz (50.2 +/- 5.7% from 23.9 +/- 2.6%, n = 19, mean +/- SEM) and 10 kHz (50.8 +/- 4.4% from 27.9 +/- 2.3%, n = 17), whereas it was significantly increased beginning on the second day in the 50 Hz group (38.9 +/- 4.6% from 23.8 +/- 2.1%, n = 17). At high intensity, both 1 and 50 Hz dorsal column stimulation reduced A alpha/beta-compound action potential size recorded at the sciatic nerve, but only 1 kHz stimulation was partially effective at the lower intensity. The number of actions potentials in C-fiber component of wide-dynamic-range neuronal response to windup-inducing stimulation was significantly decreased after 50 Hz (147.4 +/- 23.6 from 228.1 +/- 39.0, n = 13), but not 1 kHz (n = 15), dorsal column stimulation. Conclusions: Kilohertz SCS attenuated mechanical hypersensitivity in a time course and amplitude that differed from conventional 50 Hz SCS, and may involve different peripheral and spinal segmental mechanisms.