Cognitive decline in Parkinson's disease is associated with reduced complexity of EEG at baseline.

Sebastian M Keller,Volker Roth,Menorca Chaturvedi,Ute Gschwandtner,Antonia Meyer,Peter Fuhr

doi:10.1093/braincomms/fcaa207

Sebastian M Keller, Volker Roth + Show 4 more

Open Access

https://doi.org/10.1093/braincomms/fcaa207

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Abstract

Parkinson’s disease is a neurodegenerative disorder requiring motor signs for diagnosis, but showing more widespread pathological alterations from its beginning. Compared to age-matched healthy individuals, patients with Parkinson’s disease bear a 6-fold lifetime risk of dementia. For individualized counselling and treatment, prognostic biomarkers for assessing future cognitive deterioration in early stages of Parkinson’s disease are needed. In a case–control study, 42 cognitively normal patients with Parkinson’s disease were compared with 24 healthy control participants matched for age, sex and education. Tsallis entropy and band power of the δ, θ, α, β and γ-band were evaluated in baseline EEG at eyes-open and eyes-closed condition. As the θ-band showed the most pronounced differences between Parkinson’s disease and healthy control groups, further analysis focussed on this band. Tsallis entropy was then compared across groups with 16 psychological test scores at baseline and follow-ups at 6 months and 3 years. In group comparison, patients with Parkinson’s disease showed lower Tsallis entropy than healthy control participants. Cognitive deterioration at 3 years was correlated with Tsallis entropy in the eyes-open condition (P < 0.00079), whereas correlation at 6 months was not yet significant. Tsallis entropy measured in the eyes-closed condition did not correlate with cognitive outcome. In conclusion, the lower the EEG entropy levels at baseline in the eyes-open condition, the higher the probability of cognitive decline over 3 years. This makes Tsallis entropy a candidate prognostic biomarker for dementia in Parkinson’s disease. The ability of the cortex to execute complex functions underlies cognitive health, whereas cognitive decline might clinically appear when compensatory capacity is exhausted.

Highlights

While Alzheimer’s disease is the most common neurodegenerative disorder, Parkinson’s disease is the fastest growing one (Dorsey and Bloem, 2018)
Based on the Berger effect (Berger, 1929), which describes a significant decrease in power of a-band oscillations when cognitively normal participants open their eyes, it can be shown that Tsallis entropy (TE) contains non-redundant information compared to band power (BP)
In accordance with the a priori hypothesis, these results indicate that autonomous information is contained in TE

Summary

Introduction

While Alzheimer’s disease is the most common neurodegenerative disorder, Parkinson’s disease is the fastest growing one (Dorsey and Bloem, 2018). Despite being considered primarily a motor disorder, $30% of patients with Parkinson’s disease have cognitive symptoms already at initial diagnosis, and up to 80% develop cognitive symptoms at some point in their disease (Emre et al, 2007; Hely et al, 2008). Preservation and improvement of cognition in Parkinson’s disease patients have recently become major goals for therapeutic interventions and trials. Patient care and clinical trials regarding cognition currently rely mainly on bedside assessments and psychological testing with its known difficulties, including availability, reliability and test–retest biases. Biomarkers are objective monitors or predictors of the disease course and will improve making decisions for individual patients as well as for defining optimal populations for clinical trials for cognitive decline in Parkinson’s disease (Cramer, 2010; Dodakian et al, 2013)

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