Cognitive subtypes in individuals with essential tremor seeking deep brain stimulation

Objective: Essential tremor (ET) is a common neurological disorder that has been associated with 60% increased risk of developing dementia. The goals of the present study were to: (a) learn whether individuals with advanced ET symptoms seeking deep brain stimulation (DBS) surgery would fall into distinct cognitive subgroups, and (b) learn how empirically derived subgroups map onto criteria for mild cognitive impairment (MCI). Method: Patients with ET (N = 201; mean age = 68.9 ± 8.9 years) undergoing pre-surgical evaluation for DBS completed a multi-domain neurocognitive assessment consisting of memory, executive function, visuospatial skill, language, and processing speed. Two cluster analytic approaches (K-means, hierarchical) were independently conducted to classify cognitive patterns using domain composites. Demographics, clinical characteristics, and proportion of cases meeting neuropsychologically defined criteria for MCI were examined among clusters. Results: A three-cluster solution reflected a Low Executive group (N = 64), Low Memory Multi-Domain group (N = 41), and Cognitively Normal group (N = 96). The Cognitively Normal group was older and more educated, with a higher Dementia Rating Scale-2 score. In total, 27.4% of participants met criteria for MCI. Of the MCI cases, most were in the Low Executive (41.8%) or Low Memory Multi-Domain groups (49.1%). In the latter, 65.9% of its members were classified as MCI versus 35.9% in the Low Executive group. Conclusions: Our study identified three cognitive subtypes of ET patients presenting for DBS. Future work should examine the subgroups for progression to dementia, particularly the Low Memory Multi-Domain subgroup which may be at highest risk.