Objective: To summarize and review efficacy and safety evidence of pallidothalamic tractotomy (PTT) using MR-guided focused ultrasound (MRgFUS).

Background: Speigel and Wycis performed lesions in the Forel field and introduced the term “campotomy” to describe the procedure​1​ . Since then, this approach has seen a revival with PTT-MRgFUS​2​  and is being investigated as an incisionless therapy for Parkinson’s disease (PD)​3​ . A Phase III trial (NCT04728295) of staged-bilateral PTT-MRgFUS has been completed, and 12-month follow-up data are under FDA review. This systematic literature review (SLR) aims to assess the published evidence to help contextualize these upcoming results.

Method: An SLR was conducted via Medline and Medline In-Process, with no date limits (Table 1). Two reviewers independently screened titles and abstracts. Full-text review, data extraction, and narrative synthesis followed.

Results: All reports were single-center studies conducted in Switzerland (5)​4–7​ , Taiwan (2)​8,9​ , and Japan (1)​10​  (Figure 1). Unilateral PTT-MRgFUS (n=102) was an effective treatment, demonstrating statistically significant outcomes in all studies. Improvements were as high as (84%) reductions in tremor, (70%) rigidity, (73%) bradykinesia, (67%) off-medication dystonia and (38%) on-medication dyskinesias. Two staged-bilateral studies (n=25) had a mean interval of 20±10 months between the first and second PTT-MRgFUS treatments. Total off-medication UPDRS scores decreased by 52% (p<0.007). Findings on reductions in L-Dopa intake were mixed. The most common adverse events included hypoesthesia, speech difficulties, hiccups. In all the studies, no PTT related serious adverse events were reported. Recently, a modified approach was introduced by Chen et al., incorporating a dual-target VIM-PTT strategy.

Conclusion: This SLR shows PTT-MRgFUS effectively reduces motor symptoms and complications with a generally favorable safety profile. The Phase III study could expand bilateral treatment for idiopathic PD, as the first global multicenter trial investigating unilateral and staged-bilateral PTT-MRgFUS. Emerging targeting strategies highlight the need for further research to refine the optimal target, conduct larger confirmatory trials, and improve patient selection.

Inclusion and exclusion criteria

PRISMA study selection flowchart

References: 1. Spiegel, E. A. et al. Campotomy in Various Extrapyramidal Disorders. J. Neurosurg. 20, 871–884 (1963).
2. Guridi, J. & Gonzalez-Quarante, L. H. REVISITING FOREL FIELD SURGERY. World Neurosurg 147, 11–22 (2020).
3. Gallay, M. N., Jeanmonod, D., Liu, J. & Morel, A. Human pallidothalamic and cerebellothalamic tracts: anatomical basis for functional stereotactic neurosurgery. Brain Struct Funct 212, 443–463 (2008).
4. Gallay, M. N., Moser, D., Magara, A. E., Haufler, F. & Jeanmonod, D. Bilateral MR-Guided Focused Ultrasound Pallidothalamic Tractotomy for Parkinson’s Disease With 1-Year Follow-Up. Front Neurol 12, 601153 (2021).
5. Magara, A. et al. First experience with MR-guided focused ultrasound in the treatment of Parkinson’s disease. J Ther Ultrasound 2, 11 (2014).
6. Gallay, M. N. et al. MRgFUS Pallidothalamic Tractotomy for Chronic Therapy-Resistant Parkinson’s Disease in 51 Consecutive Patients: Single Center Experience. Frontiers Surg 6, 76 (2020).
7. Gallay, M. N., Moser, D., Federau, C. & Jeanmonod, D. Radiological and Thermal Dose Correlations in Pallidothalamic Tractotomy With MRgFUS. Frontiers Surg 6, 28 (2019).
8. Chen, J., Chen, C., Aoh, Y., Lu, M. & Tsai, C. Stepwise dual‐target magnetic resonance‐guided focused ultrasound in tremor‐dominant Parkinson disease: One‐year follow‐up. Eur. J. Neurol. 31, e16468 (2024).
9. Chen, J.-C., Lu, M.-K., Chen, C.-M. & Tsai, C.-H. Stepwise Dual-target MR-guided Focused Ultrasound in Tremor-dominant Parkinson’s Disease: a Feasibility Study. World Neurosurg (2022) doi:10.1016/j.wneu.2022.12.049.
10. Horisawa, S. et al. Unilateral pallidothalamic tractotomy for akinetic-rigid Parkinson’s disease: a prospective open-label study. J Neurosurg 135, 799–805 (2021).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/from-campotomy-to-mr-guided-focused-ultrasound-pallidothalamic-tractotomy-for-parkinsons-a-systematic-review-in-the-context-of-a-phase-iii-study/