Disturbances of balance and gait following high-intensity focused ultrasound ablation of subcortical brain structures: a case report

Transcranial magnetic resonance–guided focused ultrasound is a rapidly evolving noninvasive treatment modality for neurological disorders associated with movement disturbances. The greatest clinical experience has been accumulated in patients with essential tremor and Parkinson disease. Despite the minimally invasive nature of this intervention, adverse effects have been reported, including postural imbalance, which may occur in 75%–90% of cases. The most pronounced disturbances are detected in patients undergoing high-energy exposure, as well as in patients with extension of the treatment area into the subthalamic region. The present clinical observation describes the characteristics of balance disturbances and changes in gait biomechanics in a 63-year-old patient with pharmacoresistant essential tremor who underwent focused ultrasound brain surgery. As part of the preoperative assessment, magnetic resonance imaging and computed tomography of the brain were performed; based on computed tomography findings, the skull density ratio was calculated. Given the low skull density ratio, modification of the standard magnetic resonance–guided focused ultrasound protocol was performed. In the postoperative period, following high-energy exposure in the region of the left ventral intermediate nucleus of the thalamus with extension into the posterior subthalamic region, regression of tremor in the right extremities was noted; however, clinical assessment of the patient’s condition, as well as comparative stabilometric analysis in the preoperative and postoperative periods, demonstrated alterations in balance and gait. Thus, on the one hand, the unequivocal efficacy of the focused ultrasound method in essential tremor is clearly demonstrated; on the other hand, the possibility of adverse events is evident, which, despite regression of the main clinical manifestation of the disease, may lead to insufficient patient satisfaction with treatment. Further studies will help identify factors leading to balance disturbances, improve the selection of patients for focused ultrasound interventions, and develop fall-prevention programs aimed at reducing gait and balance disorders in this patient population.