Essential tremor, a disorder characterized by uncontrollable shaking in parts of the body, has been treated by medication with success. If resistance to medication builds or if there are side effects from the medication, surgical procedures can be taken, but are sometimes avoided due to invasiveness. Developments in technology allow us to use ultrasounds in place of surgery with minor side effects, but require further study prior to widespread application.
Essential tremor (ET) is a common movement disorder where involuntary shaking of various parts of the body occurs, including the hands, arms, head, larynx, tongue and chin. The disorder is not life-threatening, but can cause decreases in quality of life and socialization. The cause of ET is unknown, but is thought to involve abnormal brain waves processed by the thalamus, a brain structure responsible for muscle activity.
Treatment of ET becomes necessary when it begins to significantly interfere with a patient’s day to day life. Traditionally, a variety of medications have been used to successfully decrease the tremors associated with the disorder, but in certain patients, resistance to medications or adverse side effects may occur. In these cases, surgical procedures are an option, but are sometimes avoided due to the invasiveness of brain surgery. Fortunately, developments in ultrasound technology allow us to focus acoustic energy noninvasively to perform similar procedures. The acoustic energy is focused on areas of the thalamus responsible for tremors and destroys it, decreasing the involuntary shakes characteristic of the disorder. High-resolution imaging also allows for real-time control of the treatment. Pilot trials have shown promising results, and a research group set out to conduct a broader study.
Elias et al. set out to examine the efficacy of MRI-guided focused ultrasound thalamotomy for treatment of ET. Patients were eligible if they possessed moderate to severe ET and were refractory (resistant) to at least two trials of medication. They were subjected on a 3:1 ratio to the real treatment and a sham treatment where no acoustic energy was used as a control. Patients were confined to these groups for 3 months, after which they could switch from the sham treatment if desired. Initial tremors were diagnosed by a movement disorder specialist, and tremors were videotaped and analysed at 1, 3, 6 and 12 months after treatment. The study was published in The New England Journal of Medicine and included 76 patients.
The study determined that ultrasound thalamotomy significantly reduced hand tremor at 3 months and maintained the reduction through 12 months. The sham treatment controlled for the placebo effect, ensuring the reduction in tremor was due to treatment. Though the treatment was successful in reducing hand tremor, it provided limited benefits in reducing tremors in other parts of the body. As well, the lesions created in the treatment had adverse effects such as alteration of sensation and gait dysfunction. Further studies need to be conducted prior to application of this procedure, including comparison against current surgical procedures and determination of optimal lesion size, as larger lesions lead to more enduring effects, but also greater adverse effects.
Overall, ultrasound thalamotomy is another, less invasive treatment for ET. The lack of need for a surgical procedure is a benefit, but tremor reduction in body parts other than the hands and adverse effects should be further examined. With greater study, ultrasound thalamotomy could provide a useful treatment in improving the quality of life of those suffering from essential tremor.
Written By: Wesley Tin, BMSc