A Comparison of the Effects of Burst and Tonic Spinal Cord Stimulation on Hyperalgesia and Physical Activity in an Animal Model of Neuropathic Pain.

BACKGROUND: Parameters of spinal cord stimulation (SCS) play a role in its effectiveness and may impact SCS mechanisms and outcomes. For example, SCS applied in a bursting pattern may result in better pain relief than that for tonic SCS for neuropathic pain. We tested the effectiveness of different SCS pulse frequencies given at 2 different burst frequencies in an animal model of neuropathic pain.

METHODS: After Sprague-Dawley rats were anesthetized, neuropathic pain was induced using the spared nerve injury model, and an epidural SCS lead was implanted in the upper lumber spinal cord. One of the 8 different SCS parameters was delivered daily for 4 days at 90% motor threshold 2 weeks after nerve injury. Four burst patterns were administered at 4- or 40-Hz frequency with a train of 4 pulses at frequencies of 60, 500, and 1000 Hz. Sham and tonic patterns at 16, 60, and 160 Hz were chosen as controls. Paw withdrawal threshold was assessed before the surgery and 15 minutes before, during, and after SCS daily for 4 days. Physical activity (distance, crossing, rearing, and grooming) was assessed before surgery, before SCS on day 1, and after SCS on day 4.

RESULTS: Animals showed a decrease in paw withdrawal threshold and physical activity levels 2 weeks after nerve injury. During stimulation, burst SCS with pulse frequencies of 60, 500, or 1000 Hz were more effective for improving paw withdrawal threshold than sham and tonic SCS at 16 Hz. Burst SCS with higher pulse frequencies (500 and 1000 Hz) than 60-Hz SCS and burst SCS with higher pulse frequencies (1000 Hz) than 160-Hz SCS were more effective. In addition, tonic SCS at 160 Hz and burst SCS with higher pulse frequencies (500 and 1000 Hz) significantly increased the distance traveled. Burst SCS at 4 Hz with pulse frequency of 1000 Hz also increased the number of crossings when compared with sham control and tonic SCS at 16 Hz.

CONCLUSIONS: The current study shows that a variety of SCS pulse frequencies applied with a burst frequency result in greater improvement in hyperalgesia and activity levels than tonic SCS in a neuropathic pain model during stimulation.