BACKGROUND: Radiofrequency (RF) subthalamotomies have been proposed since the 
1960s to treat patients suffering from Parkinson's disease (PD). Recently, the 
magnetic resonance (MR)-guided focused ultrasound technology (MRgFUS) offers the 
possibility to perform subthalamic thermocoagulations with reduced risks and 
optimized accuracy. We describe here the initial results of the MRgFUS 
pallidothalamic tractotomy (PTT), an anatomical and physiological update of the 
earlier subthalamotomies.
METHODS: Thirteen consecutive patients suffering from chronic (mean disease 
duration 9.7 years) and therapy-resistant PD were treated unilaterally with an 
MRgFUS PTT. Primary relief assessment indicators were the score reduction of the 
Unified Parkinson Disease Rating Scale (UPDRS) and the patient estimation of 
global symptom relief (GSR) taken at 3 months follow-up. Final temperatures at 
target were between 52°C and 59°C. The MR examinations were performed before the 
treatment, 2 days and 3 months after it. The accuracy of the targeting was 
calculated on 2 days post-treatment MR pictures for each PTT lesion.
RESULTS: The first four patients received a PTT using the lesional parameters 
applied for thalamotomies. They experienced clear-cut recurrences at 3 months 
(mean UPDRS relief 7.6%, mean GSR 22.5%), and their MR showed no sign of thermal 
lesion in T2-weighted (T2w) images. As a consequence, the treatment protocol was 
adapted for the following nine patients by applying repetition of the final 
temperatures 4 to 5 times. That produced thermocoagulations of larger volumes 
(172 mm(3) against 83 mm(3) for the first four patients), which remained visible 
at 3 months on T2w images. These nine patients enjoyed a mean UPDRS reduction of 
60.9% and a GSR of 56.7%, very close to the results obtained with radiofrequency 
lesioning. The targeting accuracy for the whole patient group was 0.5, 0.5, and 
0.6 mm for the anteroposterior (AP), mediolateral (ML), and dorsoventral (DV) 
dimensions, respectively.
CONCLUSIONS: This study demonstrated the feasibility, safety, and accuracy of 
the MRgFUS PTT. To obtain similar results as the ones of RF PTT, it was 
necessary to integrate the fact that white matter, in this case, the 
pallidothalamic tract, requires repeated thermal exposition to achieve full 
lesioning and thus full therapeutic effect.