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

Abstract

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.

Keywords: Cognitive impairment; Depression; Essential tremor; Motor severity; Non-motor symptoms.