The emerging role of high-intensity focused ultrasound (HIFU) as a symptomatic treatment for Parkinson's disease and essential tremor: a narrative review.

The high-intensity focused ultrasound (HIFU) technique has become precise, incisionless, and ablative for treating essential tremor (ET) and Parkinson's disease (PD), driven by advances in magnetic resonance imaging (MRI) thermometry and tractography. The current review integrates the main clinical outcomes associated with established and emerging HIFU targets, synthesizing efficacy data, adverse effect (AE) patterns, and procedural characteristics relevant to clinical decision-making. In ET, ventral intermediate nucleus (VIM) thalamotomy results in tremor reductions ranging from 56 to 81%, with a long-term sustained benefit of approximately 73%. In tremor-dominant PD (TdPD), VIM ablation achieves tremor suppression of approximately 62%. Comparatively, HIFU-guided subthalamotomy provides broader motor benefits, with 53 to 57.8% improvement in the Movement Disorder Society's Unified Parkinson's Disease Rating Scale, Part III (MDS-UPDRS III), as well as significant reductions in rigidity and bradykinesia. Pallidotomy improves "off" state motor symptoms and dyskinesias, whereas pallidothalamic tractotomy leads to 52% global motor improvement and 91% tremor reduction. The AEs vary according to the targets. In VIM procedures, gait imbalance (16-40%) and sensory disturbances (9-26%) predominate, along with dysarthria and dysmetria. Lesions to the subthalamic nucleus (STN) are most commonly associated with dysarthria (10-26%) and gait instability (15-48%). Procedures targeting the globus pallidus internus (GPi) or pallidothalamic tract (PTT) may also present with gait instability or dysarthria, which are generally mild and transient. Although the SDR has historically limited eligibility, recent evidence demonstrates that patients with SDR ≤ 0.40 may still experience meaningful improvement, supporting more individualized selection. In the current therapeutic landscape, HIFU offers immediate clinical benefits, absence of implanted hardware, and simplified recovery, positioning it as an alternative or complementary therapy to deep brain stimulation (DBS).