Multi-Institutional Outcome Analysis of Gamma Knife Radiosurgery for Tremor
Ajay Niranjan, MD, MBA Sudesh S. Raju, BA L Dade Lunsford, MD
The purpose of this study is to further analyze the safety and effectiveness of GKT for a large cohort of patients afflicted with tremor. Our hypothesis is that GKT is a safe and effective treatment for the elderly or those not suitable for invasive procedures. We believe that if we can collect 200 or more patients from participating centers, this can become a powerful IGKRF study.
For nearly half a century, treatment of tremor has been surgical targeting the VIM nucleus of the thalamus, with patients of most tremor subsets experiencing some level of tremor relief. While DBS is the most common treatment for ET or PD, long term relief for MS-related tremor is less apparent. RFT is another option, sometimes performed in instances where DBS may not be financially feasible. While RFT has the ability to confirm the target site intraoperatively and slowly grow the lesion size over time, high complication rates are noted along with possible repeat procedures for sustained tremor relief.
While we believe GKT to be a safe and effective treatment option for patients with tremor, there are some notable criticisms. One such criticism is the lack of electrophysiological information to verify the target site intraoperatively. Additionally, patients typically wait 1-4 months post-GKT to experience the onset of tremor relief. However, we believe there are three main benefits of GKT. First, GKT is especially attractive for patients who are at high risk of morbidity and possible mortality from invasive procedures (DBS and RFT). These patients include the elderly (age greater than 80 years) and those with simultaneous medical morbidities, including anticoagulant therapy, respiratory, or cardiac disease. Secondly, DBS, an invasive procedure, has a high cost over time with replacement of electrodes and followup procedures. We are in agreement that if GKT produces results similar to DBS, then GKT is preferable. Finally, GKT provides radiation that extends past the 50% isodose line, with a positive effect on the kinesthetic cells within the thalamus (without cell death), through tissue destruction and physiologic alteration of the tremor region. This peripheral effect, which has been extensively studied in primates, may allow for a larger treatment volume and robust maintenance due to radiation, in comparison to RFT.