The association between motor and non-motor symptoms in essential tremor patients being evaluated for deep brain stimulation surgery

Background Non-motor symptoms, including depression and cognitive impairment, are common in essential tremor (ET), but associations between these symptoms and tremor are poorly understood. Methods A retrospective, single-institution, cohort study evaluated 140 patients with ET undergoing evaluation for deep brain stimulation (DBS) surgery. The Fahn-Tolosa-Marin (FTM) or Washington Heights-Inwood Genetic Study of ET (WHIGET) scale was used to grade tremor. Tremor scores were divided into quartiles. Patients underwent clinical neuropsychological evaluations that included a comprehensive cognitive test battery and Beck Depression Inventory-II (BDI-II). Subgroup analysis was performed with groups who met criteria for depression (BDI-II > 14) or overall cognitive impairment (<9th percentile on at least two dissimilar cognitive tests). Independent samples t-tests were used for continuous variables and chi square tests for categorical variables. Univariable and multivariable regressions were used to determine relationships between tremor and non-motor scores. Results Tremor quartile was correlated with language domain performance (p = 0.044) but not depression scores. FTM score was associated with BDI-II (β = 0.940, p = 0.010), language (β = −0.936, p = 0.012), and visuospatial domain (β = −0.836, p = 0.025) scores, such that worse tremor was associated with more depression and worse language and visuospatial function. WHIGET score was not associated with any neuropsychological scores on multivariable regression. Conclusion FTM score was associated with language, visuospatial, and mood symptoms, suggesting a relationship between the severity of these symptom types. Different tremor scores capture different motor symptoms and relationships with nonmotor symptoms.