XXV Congress of the European Society for Stereotactic and Functional Neurosurgery

Background: Safety efficacy of unilateral VIM Gamma Knife Radiosurgery (VIM GK) has been well demonstrated for Essential tremor.The safety-efficacy of bilateral VIMGK has never been assessed strictly.We conducted a prospective and objective assessed of the changes in cognitive functions (primary criteria), speech, balance in addition to the evaluation of the impact activities of daily living.Material & method: Between 03/06/2014 & 09/11/2021 have been treated contralaterally by GKS 33 patients presenting with a severe drug-resistant essential tremor previously treated by VIM GK on the dominant side at least 12 months before (monocentric, prospective, non comparative N EUDRACT: 2013-A01289-36).After frame application stereotactic MR and CTscan imaging a single isocenter of 4mm was positioned at the location of the VIM according to Guiot and adjustment of the target based on a preoperative DTi according to our usual standard technic.Quantitative assessment before, at 6 & 12 months was including neuropsychological testing (MMS, apathy Starkstein scale, Stroop, verbal fluences, similitudes), evaluation of the voice, writing, walk gait (Kinematic gait analysis was performed with the SMART TV image processing system, eMOtion), posture (AMTI force platform), tremor severity (Fahn-Tolosa-Marin rating scale) ADL (Bain Scale) and MRI (volume of T1 contrast enhancement and edema score).The assessment was perform independently from the neurosurgical team.The results were followed and reviewed by an international independent surveillance committee (MH and PK).Patients acted as their own controlsResults: All the 33 patients have completed the study after the one year follow up (19 male 14 female, 32 right VIM and 1 left).Only one adverse event (expected) was observed (hemiproprioceptive ataxia & dysarthria due to hyper-response 11 months after VIM GK).The mean age was 71 .The mean delay between the first and the second GK was 28,7 months.The primary outcome criteria of tolerance on the cognitive functions was altered in none of the patients.The evaluation of speech walk gait and posture (secondary outcome criterion) have shown no worsening.In term of efficacy at 1 year the severity score was improved of 58,5%, the disability score of 84,8% and the functional impact score of 68,6%.Only 4 patients failed to respond but for the 29 remaining the mean improvement was of 74,4% improvement of the tremor on the treated upper limb.No side effect related to the bilaterality of the VIM GKS was found in spite of the independent meticulous prospective assessment.Conclusion: This is the first prospective trial assessing the safety efficacy of bilateral VIM GK.This trial is demonstrating the excellent safety efficacy of VIM GK of the contralateral side in a subgroup of selected candidates previously treated by VIM GK at least 1 year before with a good response of the first side operated.