Basal forebrain volume and concurrent hallucinations and mild cognitive impairment in Parkinson’s disease
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Background
Visual hallucinations (VH) and mild cognitive impairment (MCI) often co-occur in Parkinson’s Disease (PD). Each symptom in isolation is associated with cholinergic basal forebrain (BF) atrophy. However, it is unclear whether BF integrity relates to one symptom preferentially or to their co-occurrence, and whether this relationship is specific to the nucleus basalis of Meynert (Ch4 & Ch4p) or extends to other BF nuclei (Ch1-2 & Ch3).
Objectives
To bridge the literature on MCI, VH, and the BF by examining associations between total and subregional BF volumes with VH, MCI, and concurrent symptomology.
Methods
We used clinical and structural MRI data in PD patients (n=296) with or without VH (n=75; n=221), and with intact cognition or MCI (n=115; n=181), evaluated prior to deep brain stimulation. One-way ANCOVAs were run for each region (total BF, Ch1-2, Ch3, Ch4, and Ch4p). The independent variable was either cognitive status, VH status, or a combined factor with three levels (Intact Cognition-noVH, MCI-noVH, and MCI-VH), and covariates included intracranial volume, age, levodopa-equivalent dose, and dopamine agonist therapy (yes/no).
Results
We demonstrate main effects of MCI on BF , Ch4 , and Ch1-2 volumes, but not of VH. Subgroup analyses show reduced BF and Ch4 volumes in patients with both symptoms ( d =0.44) relative to patients with neither.
Conclusions
We show dissociations within the cholinergic system in PD, where reduced volume of different BF nuclei relates to MCI only versus the combination of symptoms. We provide support for the “cholinergic phenotype”.
