Focused Ultrasound Unilateral Pallidotomy for Medication-Refractory Limb Dystonia

The goal of this clinical trial is to find out if a non-invasive procedure called focused ultrasound can safely and effectively treat limb dystonia in adults who have not improved with medications or botulinum toxin injections. The main questions it aims to answer are: * Does focused ultrasound reduce the severity of limb dystonia symptoms? * Is the procedure safe and well tolerated? Researchers will compare people who receive focused ultrasound treatment to those who receive a sham procedure (a look-alike procedure without active treatment) to see if the treatment works. Focused ultrasound works by producing a very small (millimeter-size) lesion in a deep brain region. In this study, the lesion is located in a region called globus pallidus, which helps control movement. Participants will: * Be randomly assigned to one of two groups: focused ultrasound or sham * Undergo a procedure using MRI and focused ultrasound to target a part of the brain called the globus pallidus * Be followed for 6 months after treatment to assess changes in symptoms, quality of life, and brain function * Participants in the sham group will be offered the real treatment after 3 months This study may offer a new non-surgical treatment option for people with dystonia affecting the arm or leg, whose pharmacological control is unsatisfactory.