122 Pulse Modulation of the Occipital Nerve Using Focused High-Intensity Ultrasound Improves Mechanical Thresholds in a Chronic Migraine Rat Model

INTRODUCTION: Chronic migraines (CM) afflict approximately 16.6% of adults and negatively impact quality of life. Furthermore, although some CM can be treated with steroids, occipital nerve block, radiofrequency therapy, or medical therapy, approximately 15% of patients remain refractory to treatment. We explore focused high-intensity ultrasound (HIU) as a therapy allowing for ablation or pulse modulation of the occipital nerve in a validated rodent model of CM. METHODS: Male Sprague-Dawley rats received inflammatory media via an epidural cannula over 3 weeks to induce a CM state. HIU was applied over the occiput to (1) ablate (n = 10) or (2) pulse modulate (n = 3) the occipital nerve. Mechanical thresholds assessed during peak headache, immediately after HIU, 24 hours post-HIU, and 48 hours post-HIU using vonFrey filaments in the forepaw, hind paw, and periorbital regions. Mechanical thresholds obtained also compared to CM rats receiving electrical occipital nerve stimulation (ONS) (n = 9) in a prior study. RESULTS: Ablation of the occipital nerve using HIU at 10 W for 3 minutes increased forepaw (P = .09) and periorbital region (P < .05, n = 10) mechanical thresholds. Pulse modulation of the occipital nerve using HIU also increased mechanical thresholds in the forepaw of CM rodents the day of and 24 hours following HIU application (P < .05, n = 2-3 rats [only two rats were tested on 2 days time point]). Pulse modulation of the occipital nerve can also produce similar improvements in mechanical thresholds to ablative focused HIU or ONS. CONCLUSION: Our results suggest that focused HIU may be an effective noninvasive treatment for refractory CM. Furthermore, by using pulse modulation instead of ablative settings, mechanical thresholds can be improved without causing damage to the occipital nerves, avoiding the aversive side effects of ablation. Future studies should address whether this noninvasive treatment is ideal and reliably effective for medically refractory CM patients.