To describe the topography of unilateral subthalamic nucleus (STN) lesions performed by magnetic-resonance guided focused ultrasound (MRgFUS) in Parkinson’s disease, and ascertain correlations between lesion size-location and improvement of cardinal signs.

Development of MRgFUS as a minimally invasive approach to lesioning deep brain structures has revitalized ablation as a therapeutic approach for movement disorders. Recently, a pilot study by Martínez-Fernández et al. (Lancet Neurology 2017) showed safety and preliminary efficacy of MRgFUS unilateral subthalamotomy for treating PD motor features.

We analyzed the volume and location of STN lesions in 31 PD patients (age 56±9.3 years) assessed at baseline and followed for 4 months. T1/T2 MR(3T) images at 24-hours post-procedure were used for assessment.    MDS-UPDRS-III was evaluated in “off” medication, after 24-hours of drug withdrawal, and sub-items for bradykinesia, rigidity and tremor were scored and analyzed independently.  

Baseline MDS-UPDRS-III off-state was 37.3±8.2 for the total score and 19±3.8 for the most affected (treated) side. Improvement on the treated side was 55.2±19.1%. Change from baseline (%) was 54.4±29, 46.6±26.8 and 74.8±27.3 for rigidity, bradykinesia and tremor respectively. Two patients developed moderate hemichorea-ballism which spontaneously resolved within 6 weeks of subthalamotomy. Averaged center lesion was located within the dorso-lateral STN motor region with a volume of 328±155.2 mm³.

Lesions associated with one cardinal sign improvement of ≥60% were considered therapeutic and those with ≤30% sub-therapeutic. Lesions with moderate improvement (30%-60%) were excluded for each sign topography analysis. Adjusted per volume, STN lesions with the greatest impact on bradykinesia were significantly more anterior than those improving tremor, which lay more laterally; rigidity reduction was related to anterior and ventral lesions.

Substantial improvement in cardinal motor features after unilateral MRgFUS subthalamotomy is related to specific lesion location within the motor STN, i.e., bradykinesia rostrally, tremor caudo-laterally and rigidity ventro-rostrally.