During focused ultrasound therapy, individual ultrasound beams pass harmlessly through tissue and then converge to a focal point at the target, where they create a hot spot. Using MRI to monitor the procedure in real time, researchers can target this focal point to ablate faulty brain circuits or unwanted tissue without needing to cut into the skull. Having previously pioneered the use of focused ultrasound to treat the most common movement disorder, essential tremor (a therapy that is now FDA approved in the USA), Elias moved on to evaluating its use in Parkinson's tremor.

The study, also conducted at Swedish Neuroscience Institute, examined 27 participants with tremor-dominant Parkinson's disease. The research team randomly assigned 20 subjects to be treated with focused ultrasound, while the others received a fake procedure (and were later offered the opportunity to undergo the actual treatment). All patients had tremor that resisted medical treatment, and all continued taking their existing Parkinson's medication.

Participants who received focused ultrasound had a 62% median improvement in their hand tremor three months later. Those who underwent a sham procedure also improved to a lesser degree, however, suggesting some placebo effect. The researchers concluded that additional tests are needed to better establish the effectiveness of focused ultrasound.

The most significant side effects reported were mild numbness on one side of the body, which improved, and persistent numbness of the face and finger. Two subjects also experienced partial weakness that recovered or improved during the study. The researchers note that the procedure has since been modified to mitigate this risk of weakness.

The research team believes that a larger, multicentre study is needed to better define the potential role of focused ultrasound in managing Parkinson's disease. "Our findings suggest that the patients likely to benefit from this approach are those for whom tremor reduction is enough to improve their quality-of-life," said University of Virginia researcher Binit Shah.