Language impairment as a risk factor for dementia conversion in parkinson's disease with mild cognitive impairment: a quantitative EEG study.

Mild cognitive impairment in Parkinson's disease (PD-MCI) is regarded as a transitory stage between normal cognition and dementia, and patients with PD-MCI have an increased risk of progression into PD dementia (PDD). We aimed to explore whether specific cognitive domain dysfunction is associated with dementia conversion in PD-MCI, and quantitative electroencephalography (qEEG) biomarkers for the domain dysfunction. We retrospectively reviewed 72 patients with PD-MCI. All patients underwent EEG and neuropsychological tests, and their cognitive conversion into PDD was assessed. We assessed five cognitive domains based on neuropsychological tests: memory, attention, language, frontal/executive, and visuospatial domain MCI. The effects of each domain dysfunction on dementia conversion were investigated using Cox regression analysis after controlling for age, sex, and education. We compared the qEEG pattern between patients with specific cognitive domain impairment, which showed a significant association with dementia conversion and its counterpart. The frequency of each cognitive domain impairment was as follows: 51 frontal/executive (70.8%), 42 attention (58.3%), 38 memory (52.8%), 27 visuospatial (37.5%), and 26 language (36.1%) impairment. Among cognitive domains, only language impairment was associated with dementia conversion (p = 0.045), and it was associated with faster conversion among the converters (p = 0.007). Language impairment was associated with higher middle beta power in the bilateral parieto-occipital regions, high beta power in the bilateral parieto-occipital regions and right frontal region, and gamma power in the bilateral occipital regions. These findings suggest that language impairment could be a prognostic marker with distinct qEEG findings in PD-MCI.