"Cognitive functioning and intra-individual variability in essential tremor and Parkinson's disease: A comparative
Hannah L Combs1, Samantha K Henry1, Troy A Webber2,3,4
1Department of Neurology, Baylor College of Medicine, Houston, TX.
The Clinical Neuropsychologist
|June 16, 2025
Summary
Essential tremor (ET) patients show increased intraindividual variability (IIV-D) in cognitive function compared to healthy controls, even without a formal diagnosis. This finding highlights potential neurological differences in ET, suggesting IIV-D as a key marker.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Neurology
Background:
- Cognitive decline may be more common in essential tremor (ET) than previously understood.
- Dispersion-based intraindividual variability (IIV-D) is a proposed indicator of neurological integrity.
- Elevated IIV-D is documented in Parkinson's disease (PD), but not yet studied in ET.
Purpose of the Study:
- To investigate cognitive functioning and IIV-D in individuals with ET.
- To compare cognitive performance and IIV-D between ET, PD, and cognitively intact controls (IC).
Main Methods:
- Retrospective analysis of neuropsychological data from 188 PD, 53 ET, and 135 IC patients.
- Calculation of IIV-D using intraindividual standard deviation (iSD) and coefficient of variance (CoV) across 13 neurocognitive scores.
- Secondary analysis of IIV-D in a subset of participants with 'No Cognitive Disorder' (NCD).
Main Results:
- Both PD and ET groups performed worse than IC on measures of processing speed, mental tracking, set-shifting, and semantic fluency.
- Greater IIV-D was observed in both PD and ET compared to IC when using CoV.
- Individuals with ET exhibited greater IIV-D than IC, even within the NCD subset, when using CoV.
Conclusions:
- This study is the first to demonstrate increased IIV-D in individuals with ET compared to controls, irrespective of a formal neurocognitive diagnosis.
- Findings suggest that IIV-D may serve as a valuable marker for cognitive alterations in ET.
- Further research is needed to explore potential clinical confounds such as medications and motor severity.
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