Objective: To study the prevalence of pain and the and the effect of scalp block on pain scores during Magnetic resonance guided focused ultrasound (MRgFUS) thalamotomy in patients with essential tremor (ET) treated at the Walton Centre NHS Foundation Trust, Liverpool, UK.

Background: MRgFUS thalamotomy is an emerging treatment for movement disorders, including essential tremor. Whilst incisionless, pain during stereotactic frame insertion and sonication can be significant. Previous studies have primarily used local anaesthesia infiltration to pin sites rather than scalp block. The effect of scalp block on overall pain is not well characterised.

Method: The following data were collected prospectively between February 2025 and February 2026: demographic characteristics, ASA grade, skull density ratio (SDR), maximum energy used during sonication (in Joules), procedural parameters and pain characteristics were recorded. Pain was measured by using numerical rating scale (NRS) from 0-10, classified into mild (0-3), moderate (4-6) or severe (7-10). Ethics approval was covered by the Walton Centre biobank.

Results: A total of 42 patients were included (29 male, 13 female). Age ranged from 51-83, (mean 72.23). Energy delivered ranged from 6,048-32,224 J (mean 13,641.8 J). ASA distribution: 1 (n=4), 2 (n=25), 3 (n=13). Skull density ratio ranged 0.35-0.76 (mean 0.537). 1 patient experienced mild pain on frame insertion, 8 patients reported pain during sonication. 4 mild, 2 moderate and 2 severe. Of those reporting severe pain during sonication, the SDR average was 0.38 (range 0.35-0.42) compared with 0.53 (range 0.37-0.76) in those not reporting pain. In addition, the average energy in those reporting severe pain was 30934J versus 12062J in those without pain. This suggests that lower SDR and higher energy delivery were associated with increased pain during sonication. Post-treatment tremor control averaged 88.17% (range 50-100%).

Conclusion: Scalp block appears to reduce procedural pain during MRgFUS thalamotomy, likely via blockade of scalp and periosteal nociceptors. Severe pain during sonication was minimal (4.7%)in patients receiving scalp block. In contrast, previous studies without scalp block have reported higher rates of sonication pain, with 66% describing it as severe [1]. Larger-scale studies are required to confirm these findings and standardise anaesthetic protocols for MRgFUS procedures.

References: [1] He X, Oshino S, Hosomi K, Kanemoto M, Tani N, Kishima H. Characteristics of Pain During MRI-Guided Focused Ultrasound Thalamotomy. Neurosurgery. 2023 Aug 1;93(2):358-365. doi: 10.1227/neu.0000000000002420.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/prevalence-of-pain-and-effect-of-scalp-block-on-pain-scores-during-mri-guided-focused-ultrasound-lesioning-procedure/