Gamma-Knife Thalamotomy for Essential and Parkinsonian Tremor: Predicting Response to Treatment Using Pre-Therapeutic Cerebral FDG-PET

Essential tremor and parkinsonian tremor affect approximately 5–7% of individuals over the age of 65. Pharmacological therapies yield sustained clinical improvement in only about 50% of cases. For patients ineligible for deep brain stimulation, Gamma Knife thalamotomy (GKVIM) offers a non-invasive alternative, demonstrating a tremor reduction efficacy of 70–80%, typically with a latency of approximately 4.8 months. This study aimed to identify regional cerebral metabolic patterns predictive of clinical response to GKVIM using [¹<sup>8</sup>F]-FDG positron emission tomography (FDG-PET). Fifteen consecutive patients diagnosed with essential tremor (n=10) or parkinsonian tremor (n=5) underwent preoperative cerebral FDG-PET imaging within 24 hours prior to GKVIM at Erasme University Hospital between January 2020 and January 2023. All patients were clinically followed for a minimum of six months (mean follow-up: 9 ± 3 months) by experienced neurologists or neurosurgeons. Statistical Parametric Mapping (SPM) was used to compare metabolic patterns between treatment responders (n=11; 73%) and non-responders (n=4) to identify potential predictors of therapeutic response. As a secondary objective, metabolic differences between patients with essential tremor and healthy controls (n=54) were analyzed to explore neurobiological correlates of disease pathophysiology. Those analysis revealed that responders exhibited significant hypometabolism in the prefrontal cortex and supramarginal gyrus, alongside cerebellar hypermetabolism. In the secondary analysis, patients with essential tremor demonstrated distinct metabolic alterations, notably involving the inferior olivary nuclei. This study thus identifies specific regional cerebral metabolic patterns associated with favourable clinical response to Gamma Knife thalamotomy, suggesting potential neuroimaging biomarkers for patient selection. Moreover, the observed metabolic changes provide additional insight into the pathophysiological mechanisms underlying essential tremor.