Introduction: Chronic migraines (CM) afflict approximately 16.6% of adults and negatively impact quality of life. Furthermore, while 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, 24h post-HIU, and 48h post-HIU using vonFrey filaments in the forepaw, hind paw and peri-orbital 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 10W for 3 minutes increased forepaw (p=0.09) and peri-orbital region (p<0.05, n=10, Figure 1) mechanical thresholds. Pulse modulation of the occipital nerve using HIU also increased mechanical thresholds in the forepaw of CM rodents the day of and 24h following HIU application (p<0.05, n=2-3 rats (only two rats were tested on 2day time point), Figure 2). Pulse modulation of the occipital nerve can also produce similar improvements in mechanical thresholds to ablative focused HIU or ONS (Figure 1).

Conclusions: Our results suggest that focused HIU may be an effective noninvasive treatment for refractory CM. Furthermore, 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.

Patient Care: Pulse-modulated HIFU presents a potential non-invasive, fast, and clinically applicable treatment for chronic migraine. HIFU could potentially be used in cases refractory to current treatments and, due to its speed of application and fast action, could potentially break the pain cycle for these patients.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Appreciate that mechanical thresholds are decreased by Chronic Migraine, and experience an increase following application of HIFU to the occipital nerve. 2) Discuss how both ablative and pulse modulated HIFU have resulted in increased mechanical thresholds.

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